From the Cover: Anthropogenic changes in sodium affect neural and muscle development in butterflies

The development of organisms is changing drastically because of anthropogenic changes in once-limited nutrients. Although the importance of changing macronutrients, such as nitrogen and phosphorus, is well-established, it is less clear how anthropogenic changes in micronutrients will affect organismal development, potentially changing dynamics of selection. We use butterflies as a study system to test whether changes in sodium availability due to road salt runoff have significant effects on the development of sodium-limited traits, such as neural and muscle tissue. We first document how road salt runoff can elevate sodium concentrations in the tissue of some plant groups by 1.5–30 times. Using monarch butterflies reared on roadside- and prairie-collected milkweed, we then show that road salt runoff can result in increased muscle mass (in males) and neural investment (in females). Finally, we use an artificial diet manipulation in cabbage white butterflies to show that variation in sodium chloride per se positively affects male flight muscle and female brain size. Variation in sodium not only has different effects depending on sex, but also can have opposing effects on the same tissue: across both species, males increase investment in flight muscle with increasing sodium, whereas females show the opposite pattern. Taken together, our results show that anthropogenic changes in sodium availability can affect the development of traits in roadside-feeding herbivores. This research suggests that changing micronutrient availability could alter selection on foraging behavior for some roadside-developing invertebrates.The development of fitness-related traits is closely tied to nutrition—from fecundity being influenced by protein availability (1, 2) to ornament coloration being linked to carotenoid abundance (3, 4). However, humans are having a major impact on the availability of many nutrients important in the development of these traits. For instance, nitrogen and phosphorus availability has increased dramatically because of fertilizer application (5, 6), with drastic consequences for biomass and nutrient content of producers and consumers (7–9). Although the effects of changing macronutrients have been well-studied, the importance of human-induced changes in micronutrients is less established. Are anthropogenic changes in once-limited micronutrients enough to drive differences in trait development, potentially altering selection dynamics?This research focuses on changing availability of an important micronutrient: sodium. Sodium is a key component of animal development, important for the function of neural and muscle tissue (10–12) and affecting the development of traits, such as brain size (13–16). However, sodium availability is limited in most ecosystems (17–19), which is thought to have led to the evolution of sodium cravings (20, 21) and specific foraging behavior to acquire sodium (22–25). Humans are increasing sodium availability, particularly through the application of road salt (26–29) but also, through agricultural activity (30). In the metropolitan area of Minneapolis and St. Paul, Minnesota, ∼300,000 tons of sodium chloride are applied to roads each winter (31). Research on the ecological impact of road salt has mostly focused on the negative effects of chloride entering waterways (32–34). However, road salt application can also increase the availability of dietary sodium for animals. A handful of studies suggest that road salt application may affect sodium foraging in animals from ants to moose (35, 36). We know little about whether local increases in sodium along roadsides have significant effects on development of fitness-related traits for species feeding along roadsides, thus altering evolutionary dynamics in the anthropocene.Butterflies are an excellent study system to test the consequences of changing sodium availability. Sodium availability has been shown to affect the development and activity of flight muscle in male Lepidoptera (37–39). Many adult male Lepidoptera actively forage for sodium through puddling, transferring much of this sodium to females during mating (23, 40–43). In addition, host plants of many butterfly species commonly grow along roadsides and would be affected by roadside runoff. Butterfly larvae also have limited movement (44, 45), such that the spatially restricted effects of salt runoff are biologically relevant. This work starts by documenting the effects of roadside salt runoff on sodium availability in common butterfly host plants. Two rearing experiments—one using roadside-collected and control host plants and the other using a controlled artificial diet manipulation—show the importance of changing sodium availability on trait development. In particular, we focus on two fitness-related traits—muscle and neural tissue—where sodium availability has a shown importance in trait development and function.     

Heterotrophic feeding as a newly identified survival strategy of the dinoflagellate Symbiodinium

Survival of free-living and symbiotic dinoflagellates (Symbiodinium spp.) in coral reefs is critical to the maintenance of a healthy coral community. Most coral reefs exist in oligotrophic waters, and their survival strategy in such nutrient-depleted waters remains largely unknown. In this study, we found that two strains of Symbiodinium spp. cultured from the environment and acquired from the tissues of the coral Alveopora japonica had the ability to feed heterotrophically. Symbiodinium spp. fed on heterotrophic bacteria, cyanobacteria (Synechococcus spp.), and small microalgae in both nutrient-replete and nutrient-depleted conditions. Cultured free-living Symbiodinium spp. displayed no autotrophic growth under nitrogen-depleted conditions, but grew when provided with prey. Our results indicate that Symbiodinium spp.'s mixotrophic activity greatly increases their chance of survival and their population growth under nitrogen-depleted conditions, which tend to prevail in coral habitats. In particular, free-living Symbiodinium cells acquired considerable nitrogen from algal prey, comparable to or greater than the direct uptake of ammonium, nitrate, nitrite, or urea. In addition, free-living Symbiodinium spp. can be a sink for planktonic cyanobacteria (Synechococcus spp.) and remove substantial portions of Synechococcus populations from coral reef waters. Our discovery of Symbiodinium's feeding alters our conventional views of the survival strategies of photosynthetic Symbiodinium and corals.     

Disentangling the mechanisms behind climate effects on zooplankton

Understanding how climate influences ecosystems is complicated by the many correlated and interrelated impacting factors. Here we quantify climate effects on Calanus finmarchicus in the northeastern Norwegian Sea and southwestern Barents Sea. By combining oceanographic drift models and statistical analyses of field data from 1959 to 1993 and investigating effects across trophic levels, we are able to elucidate pathways by which climate influences zooplankton. The results show that both chlorophyll biomass in spring and C. finmarchicus biomass in summer relate positively to a combination of shallow mixed layer depth and increased wind in spring, suggesting that C. finmarchicus biomass in summer is influenced by bottom-up effects of food availability. Furthermore, spatially resolved C. finmarchicus biomass in summer is linked to favorable transport from warmer, core areas to the south. However, increased mean temperature in spring does not lead to increased C. finmarchicus biomass in summer. Rather, spring biomass is generally higher, but population growth from spring to summer is lower, after a warm compared with a cold spring. Our study illustrates how improved understanding of climate effects can be obtained when different datasets and different methods are combined in a unified approach.Climate change and variability have been correlated to various responses in zooplankton phenology, distribution, abundance, and composition (1, 2), but the controlling mechanisms behind the associations are often elusive. For example, a change in temperature might directly affect zooplankton physiology (3) or indirectly influence zooplankton through effects on their prey (4) or ecosystem trophic structure (5). To make realistic projections of climate effects on marine ecosystems, there is a need for improved understanding of the mechanisms by which climate affects the different trophic levels.The Atlantic waters of the Norwegian Sea–Barents Sea (NS–BS) host a highly productive ecosystem including several large fish stocks of high socioeconomic importance (6). The area experienced increased water temperatures during the past decades (7) and is, like other high-latitude regions, predicted to warm substantially throughout the 21st century (8). Climate simulations further suggest globally increased ocean stratification, accompanied by decreased primary production in temperate regions but increased primary production in the subarctic (including the Barents Sea) (9, 10).Calanus finmarchicus dominates mesozooplankton biomass and is an important predator on phytoplankton throughout the North Atlantic (11, 12). In the NS–BS, young stages of C. finmarchicus are preyed upon by larvae of demersal fish, and older stages are preyed upon by various pelagic stocks (12, 13). Several studies have indicated that C. finmarchicus in the NS–BS is top-down controlled, particularly by Barents Sea capelin (14–16) and Norwegian spring spawning herring (17, 18). Consistent effects of climate or food availability have on the other hand rarely been demonstrated in situ (19–21).Investigating environmental effects on zooplankton dynamics from field data is challenging due to the influence of advection (22). Individual-based particle tracking models are considered a valuable tool to incorporate the role of advection (23), but although the results of such models commonly are compared and calibrated with observation data, they are rarely directly used in statistical analyses of observation data (but see refs. 24–26).In this study, we combine spatially resolved data on C. finmarchicus from biannual surveys in the NS–BS from 1959 to 1993 (Fig. 1) with particle tracking to disentangle the mechanisms behind climate effects on zooplankton. Specifically, we aim to understand how C. finmarchicus biomass in summer (the second survey each year) is influenced by (i) advection from observed distributions in spring (the first survey) and variation in (ii) temperature, (iii) mixed layer depth (MLD), and (iv) wind (a proxy for mixing and turbulence) in spring. For this purpose, we simulated the drift of C. finmarchicus from spring to summer and used environmental conditions along drift trajectories in spring, according to an ocean model hindcast (27), in a statistical analysis of observed summer biomass. Furthermore, we investigated how these environmental conditions influence (i) year-to-year variation in C. finmarchicus summer biomass and (ii) ambient chlorophyll (Chl) in spring, a proxy for food availability.Open in a separate windowFig. 1.(A) Map of the study area and the position of C. finmarchicus survey stations (dashed box). The main surface currents in the area are the North Atlantic Current (red solid arrows), the Norwegian Coastal Current (green dotted arrows), and Arctic Water Currents (blue dashed arrows). The 500-m depth contour (gray line) marks the approximate division between the Norwegian Sea (NS) and the Barents Sea (BS) and Norwegian continental shelf (NCS). (B) Survey stations, pooled for all years and separated in stations from spring (bullets) and summer (open circles). Stations removed from the statistical analyses of C. finmarchicus biomass in summer are marked as gray (Materials and Methods). Particles simulating C. finmarchicus were released within the gray shaded area in spring.We show how combining state-of-the art drift modeling, spatial statistical analyses, and time series analyses of long-term survey data can improve our understanding of the mechanisms behind climate effects in marine systems. By investigating effects across trophic levels, we highlight how changes in water column properties can influence food conditions for zooplankton and in turn the zooplankton biomass available as prey for higher trophic levels.     

Long-term effects of a trophic cascade in a large lake ecosystem

Introductions or invasions of nonnative organisms can mediate major changes in the trophic structure of aquatic ecosystems. Here we document multitrophic level impacts in a spatially extensive system that played out over more than a century. Positive interactions among exotic vertebrate and invertebrate predators caused a substantial and abrupt shift in community composition resulting in a trophic cascade that extended to primary producers and to a nonaquatic species, the bald eagle. The opossum shrimp, Mysis diluviana, invaded Flathead Lake, Montana, the largest freshwater lake in the western United States. Lake trout had been introduced 80 y prior but remained at low densities until nonnative Mysis became established. The bottom-dwelling mysids eliminated a recruitment bottleneck for lake trout by providing a deep water source of food where little was available previously. Lake trout subsequently flourished on mysids and this voracious piscivore now dominates the lake fishery; formerly abundant kokanee were extirpated, and native bull and westslope cutthroat trout are imperiled. Predation by Mysis shifted zooplankton and phytoplankton community size structure. Bayesian change point analysis of primary productivity (27-y time series) showed a significant step increase of 55 mg C m(-2) d(-1) (i.e., 21% rise) concurrent with the mysid invasion, but little trend before or after despite increasing nutrient loading. Mysis facilitated predation by lake trout and indirectly caused the collapse of kokanee, redirecting energy flow through the ecosystem that would otherwise have been available to other top predators (bald eagles).     

Grass roots chemistry: meta-tyrosine, an herbicidal nonprotein amino acid

Fine fescue grasses displace neighboring plants by depositing large quantities of an aqueous phytotoxic root exudate in the soil rhizosphere. Via activity-guided fractionation, we have isolated and identified the nonprotein amino acid m-tyrosine as the major active component. m-Tyrosine is significantly more phytotoxic than its structural isomers o- and p-tyrosine. We show that m-tyrosine exposure results in growth inhibition for a wide range of plant species and propose that the release of this nonprotein amino acid interferes with root development of competing plants. Acid hydrolysis of total root protein from Arabidopsis thaliana showed incorporation of m-tyrosine, suggesting this as a possible mechanism of phytotoxicity. m-Tyrosine inhibition of A. thaliana root growth is counteracted by exogenous addition of protein amino acids, with phenylalanine having the most significant effect. The discovery of m-tyrosine, as well as a further understanding of its mode(s) of action, could lead to the development of biorational approaches to weed control.     

Effect of trans fatty acid intake on abdominal and liver fat deposition and blood lipids: a randomized trial in overweight postmenopausal women

Background:

Intake of industrially produced trans fatty acids (TFAs) is, according to observational studies, associated with an increased risk of cardiovascular disease, but the causal mechanisms have not been fully elucidated. Besides inducing dyslipidemia, TFA intake is suspected to promote abdominal and liver fat deposition.

Objective:

We examined the effect of a high intake of TFA as part of an isocaloric diet on whole-body, abdominal and hepatic fat deposition, and blood lipids in postmenopausal women.

Methods:

In a 16-week double-blind parallel intervention study, 52 healthy overweight postmenopausal women were randomized to receive either partially hydrogenated soybean oil providing 15.7 g day⁻¹ of TFA or a control oil with mainly oleic and palmitic acid. Before and after the intervention, body composition was assessed by dual-energy X-ray absorptiometry, abdominal fat by magnetic resonance (MR) imaging, and liver fat by ¹H MR spectroscopy.

Results:

Compared with the control fat, TFA intake decreased plasma high-density lipoprotein (HDL)-cholesterol by 10%, increased low-density lipoprotein (LDL)-cholesterol by 18% and resulted in an increased LDL/HDL-cholesterol ratio (baseline adjusted mean (95% CI) difference between diet groups 0.41 (0.22; 0.60); P<0.001). TFA tended to increase the body fat (0.46 (−0.20; 1.17) kg; P=0.16) and waist circumference (1.1 (−0.1; 2.4) cm; P=0.08) more than the control fat, whereas neither abdominal nor liver fat deposition was affected by TFA.

Conclusion:

The adverse effect of dietary TFA on cardiovascular disease risk involves induction of dyslipidemia, and perhaps body fat, whereas weight gain-independent accumulation of ectopic fat could not be identified as a contributory factor during short-term intake.     

Helicobacter pylori infection is not associated with nonalcoholic fatty liver disease

AIM: To determine whether Helicobacter pylori(H. pylori) infection confers a higher risk of Nonalcoholic fatty liver disease(NAFLD).METHODS: Healthy people who underwent health screening were analyzed retrospectively. Inclusion criteria were age ≥ 20 years, history of H. pylori infection, and recorded insulin level. Participants were classified as H. pylori positive or negative according to 13 C urea breath tests. NAFLD was defined using the hepatic steatosis index(HSI) and NAFLD liver fat score(NAFLD-LFS). Those with an HSI 36 or NAFLD-LFS -0.640 were considered to have NAFLD. Multivariable logistic regression was performed to identify risk factors for NAFLD.RESULTS: Three thousand six hundred and sixtythree people were analyzed and 1636(44.7%) were H. pylori positive. H. pylori infection was associated with older age, male gender, hypertension, higher body mass index, and a dyslipidemic profile. HSI differed significantly between H. pylori positive and negative subjects(median 33.2, interquartile range(IQR) 30.0-36.2 for H. pylori-positive vs median 32.6, IQR 29.8-36.0 for negative participants, P = 0.005), but NAFLD-LSF did not [median-1.7, IQR-2.4--0.7 vs median-1.8, IQR-2.4-(-0.7), respectively, P = 0.122]. The percentage of people with NAFLD did not differbetween infected and uninfected groups: HIS, 26.9% vs 27.1%, P = 0.173; NAFLD-LFS, 23.5% vs 23.1%, P = 0.778. H. pylori infection was not a risk factor, but C-reactive protein concentration and smoking were significant risk factors for NAFLD.CONCLUSION: H. pylori infection is not a risk factor for NAFLD as indicated by HSI or NAFLD-LFS. Prospective, large-scale studies involving liver biopsies should be considered.     

Protistan grazing impacts microbial communities and carbon cycling at deep-sea hydrothermal vents

Microbial eukaryotes (or protists) in marine ecosystems are a link between primary producers and all higher trophic levels, and the rate at which heterotrophic protistan grazers consume microbial prey is a key mechanism for carbon transport and recycling in microbial food webs. At deep-sea hydrothermal vents, chemosynthetic bacteria and archaea form the base of a food web that functions in the absence of sunlight, but the role of protistan grazers in these highly productive ecosystems is largely unexplored. Here, we pair grazing experiments with a molecular survey to quantify protistan grazing and to characterize the composition of vent-associated protists in low-temperature diffuse venting fluids from Gorda Ridge in the northeast Pacific Ocean. Results reveal protists exert higher predation pressure at vents compared to the surrounding deep seawater environment and may account for consuming 28 to 62% of the daily stock of prokaryotic biomass within discharging hydrothermal vent fluids. The vent-associated protistan community was more species rich relative to the background deep sea, and patterns in the distribution and co-occurrence of vent microbes provide additional insights into potential predator–prey interactions. Ciliates, followed by dinoflagellates, Syndiniales, rhizaria, and stramenopiles, dominated the vent protistan community and included bacterivorous species, species known to host symbionts, and parasites. Our findings provide an estimate of protistan grazing pressure within hydrothermal vent food webs, highlighting the important role that diverse protistan communities play in deep-sea carbon cycling.

Mixing of hydrothermal vent fluids with surrounding seawater in the deep sea creates redox gradients that promote a hub of biological activity supported by chemosynthetic primary production in the absence of sunlight. These localized regions of elevated microbial biomass are important sources of carbon and energy to the surrounding deep-sea ecosystem (1–5). In particular, the consumption of hydrothermal vent microorganisms by single-celled microbial eukaryotes (or protists) is an important link in the food web in which carbon is transferred to higher trophic levels or remineralized to the microbial loop.Protistan grazing is a significant source of mortality for bacterial and archaeal populations in aquatic ecosystems that also influences their composition and diversity (6). Assessments of grazing in the mesopelagic and dark ocean indicate that rates of consumption decrease with depth and correspond to bacterial abundance (7, 8). Therefore, at sites of increased biological activity and microbial biomass, such as areas of redox stratification, protistan grazing is higher relative to the rest of the water column (9, 10). Comparable data are lacking from deep-sea hydrothermal vents, in which the relatively high microbial biomass and rates of primary productivity suggest protistan grazing should be a significant source of microbial mortality and carbon transfer. Furthermore, single-celled microbial eukaryotes can serve as a nutritional resource for other larger protists and higher trophic levels (4, 11).Early microscopic and culture-based experiments from several hydrothermal vents confirmed the presence of single-celled microbial eukaryotes, with observations and enrichment cultures revealing diverse assemblages of ciliates and flagellated protists (12, 13). The study of protistan taxonomy and distribution via genetic analyses at deep-sea vents has uncovered a community largely composed of alveolates, stramenopiles, and rhizaria (14–17). In addition to many of these sequence surveys identifying known bacterivorous species, ciliates isolated from Guaymas Basin were shown to consume an introduced prey analog (18). Collectively, these studies provide supporting evidence of a diverse community of active protistan grazers at deep-sea vents.Here, we investigate protistan predation pressure upon microbial populations in venting fluids along the Gorda Ridge to test the hypothesis that protistan grazing and diversity is elevated within hydrothermal habitats compared to the surrounding deep sea due to increased prey availability. Estimates of mortality via protistan phagotrophy are calculated from grazing experiments conducted with low-temperature, diffusely venting fluid that mixes with seawater at and below the seafloor. Paired 18S ribosomal RNA (rRNA) gene amplicon sequencing from the same experimental sites and incubations reveals the in situ protistan diversity and distribution to evaluate potential preferences in prey, with a focus on the protistan grazer population and their relationship to bacteria and archaea. We present quantitative estimates of protistan grazing from a deep-sea hydrothermal vent ecosystem, thus providing details into the role protists play in food webs and carbon cycling in the deep sea.     

Microbiome as mediator: Do systemic infections start in the gut?

The intestinal microbiome is emerging as a crucial mediator between external insults and systemic infections. New research suggests that our intestinal microorganisms contribute to critical illness and the development of non-gastrointestinal infectious diseases.Common pathways include a loss of fecal intestinal bacterial diversity and a disproportionate increase in toxogenic bacterial species. Therapeutic interventions targeting the microbiome- primarily probiotics- have yielded limited results to date. However, knowledge in this area is rapidly expanding and microbiome-based therapy such as short-chain fatty acids may eventually become a standard strategy for preventing systemic infections in the context of critical illness.     

Pleistocene to historic shifts in bald eagle diets on the Channel Islands,California

Studies of current interactions among species, their prey, and environmental factors are essential for mitigating immediate threats to population viability, but the true range of behavioral and ecological flexibility can be determined only through research on deeper timescales. Ecological data spanning centuries to millennia provide important contextual information for long-term management strategies, especially for species that now are living in relict populations. Here we use a variety of methods to reconstruct bald eagle diets and local abundance of their potential prey on the Channel Islands from the late Pleistocene to the time when the last breeding pairs disappeared from the islands in the mid-20th century. Faunal and isotopic analysis of bald eagles shows that seabirds were important prey for immature/adult eagles for millennia before the eagles’ local extirpation. In historic times (A.D. 1850–1950), however, isotopic and faunal data show that breeding bald eagles provisioned their chicks with introduced ungulates (e.g., sheep), which were locally present in high densities. Today, bald eagles are the focus of an extensive conservation program designed to restore a stable breeding population to the Channel Islands, but native and nonnative prey sources that were important for bald eagles in the past are either diminished (e.g., seabirds) or have been eradicated (e.g., introduced ungulates). In the absence of sufficient resources, a growing bald eagle population on the Channel Islands could expand its prey base to include carrion from local pinniped colonies, exert predation pressure on a recovering seabird population, and possibly prey on endangered island foxes.     

Shifts in metabolic scaling,production, and efficiency across major evolutionary transitions of life

The diversification of life involved enormous increases in size and complexity. The evolutionary transitions from prokaryotes to unicellular eukaryotes to metazoans were accompanied by major innovations in metabolic design. Here we show that the scalings of metabolic rate, population growth rate, and production efficiency with body size have changed across the evolutionary transitions. Metabolic rate scales with body mass superlinearly in prokaryotes, linearly in protists, and sublinearly in metazoans, so Kleiber’s 3/4 power scaling law does not apply universally across organisms. The scaling of maximum population growth rate shifts from positive in prokaryotes to negative in protists and metazoans, and the efficiency of production declines across these groups. Major changes in metabolic processes during the early evolution of life overcame existing constraints, exploited new opportunities, and imposed new constraints.     

Evasion of peptide, but not lipid antigen presentation, through pathogen-induced dendritic cell maturation

Dendritic cells (DC) present lipid and peptide antigens to T cells on CD1 and MHC Class II (MHCII), respectively. The relative contribution of these systems during the initiation of adaptive immunity after microbial infection is not characterized. MHCII molecules normally acquire antigen and rapidly traffic from phagolysosomes to the plasma membrane as part of DC maturation, whereas CD1 molecules instead continually recycle between these sites before, during, and after DC maturation. We find that in Mycobacterium tuberculosis (Mtb)-infected DCs, CD1 presents antigens quickly. Surprisingly, rapid DC maturation results in early failure and delay in MHCII presentation. Whereas both CD1b and MHCII localize to bacterial phagosomes early after phagocytosis, MHCII traffics from the phagosome to the plasma membrane with a rapid kinetic that can precede antigen availability and loading. Thus, rather than facilitating antigen presentation, a lack of coordination in timing may allow organisms to use DC maturation as a mechanism of immune evasion. In contrast, CD1 antigen presentation occurs in the face of Mtb infection and rapid DC maturation because a pool of CD1 molecules remains available on the phagolysosome membrane that is able to acquire lipid antigens and deliver them to the plasma membrane.     

Lactic acid production by Streptococcus thermophilus alters Clostridium difficile infection and in vitro Toxin A production

Antibiotic treatment to treat specific infections has the potential to effectively target the offending microbe as well as other microbes that colonize sites within a host. Antibiotic-associated diarrhea (AAD) is a classic example resulting from disruption of host microbial communities; 20% of patients with AAD are likely to become colonized with Clostridium difficile. Restoration of a “normal” microbial community within the host using probiotic bacteria is one approach to circumvent AAD and C. difficile infection. The goals of this study were to assess the interactions between Streptococcus thermophilus, a potential probiotic organism and C. difficile using both in vitro and in vivo systems. Exposure of C. difficile to filtered supernatants from S. thermophilus showed a dose-dependent, bactericidal effect due to lactic acid. Additional studies show that levels of lactic acid (10 mM) that did not inhibit bacterial growth had the potential to decrease tcdA expression and TcdA release into the extracellular milieu. In vivo, treatment with viable S. thermophilus significantly increased luminal levels of lactate in the cecum compared with UV-irradiated S. thermophilus. In the context of infection with C. difficile, mice treated with viable S. thermophilus exhibited 46% less weight loss compared with untreated controls; moreover, less pathology, diarrhea, and lower detectable toxin levels in cecal contents were evident more often in S. thermophillus treated mice. A significant, inverse correlation (Spearman r = -0.942, p = 0.017) between the levels of luminal lactate and abundance of C. difficile were noted suggesting that lactate produced by S. thermophilus is a factor impacting the progression of C. difficile infection in the murine system.     

Synthesis and degradation of dinoflagellate plastid-encoded psbA proteins are light-regulated, not circadian-regulated

In many dinoflagellate species, the plastid genome has been proposed to exist as a limited number of single-gene minicircles, and many genes normally found in the plastid genome are nuclear-encoded. Unlike the nuclear-encoded plastid-directed gene products whose expression is often regulated by the circadian clock, little is known about expression of minicircle genes. Furthermore, even the plastid location of the minicircles has recently been challenged. We have examined the incorporation in vivo of [(35)S]methionine into the proteins of purified plastids, and we find that several plastid proteins are labeled in the presence of cycloheximide but not chloramphenicol. One of these proteins, labeled in two different dinoflagellate species, was identified as psbA by Western blot analysis. Furthermore, this psbA has the expected physiological characteristics, because both synthesis and degradation are induced by light. We find no evidence for circadian control over either synthesis or degradation of psbA, unlike the several nuclear-encoded plastid-directed proteins studied. Finally, we find that levels of psbA protein or RNA do not change over a 24-h light-dark cycle, suggesting that this protein may not be involved in mediating the circadian rhythm in oxygen evolution rates. This demonstration is the first, to our knowledge, that minicircle genes encoding plastid proteins are translated in dinoflagellate plastids, and it suggests that a proteomic approach to characterizing the dinoflagellate plastid genome is feasible.     

Omega-3 deficiency impairs honey bee learning

Deficiency in essential omega-3 polyunsaturated fatty acids (PUFAs), particularly the long-chain form of docosahexaenoic acid (DHA), has been linked to health problems in mammals, including many mental disorders and reduced cognitive performance. Insects have very low long-chain PUFA concentrations, and the effect of omega-3 deficiency on cognition in insects has not been studied. We show a low omega-6:3 ratio of pollen collected by honey bee colonies in heterogenous landscapes and in many hand-collected pollens that we analyzed. We identified Eucalyptus as an important bee-forage plant particularly poor in omega-3 and high in the omega-6:3 ratio. We tested the effect of dietary omega-3 deficiency on olfactory and tactile associative learning of the economically highly valued honey bee. Bees fed either of two omega-3–poor diets, or Eucalyptus pollen, showed greatly reduced learning abilities in conditioned proboscis-extension assays compared with those fed omega-3–rich diets, or omega-3–rich pollen mixture. The effect on performance was not due to reduced sucrose sensitivity. Omega-3 deficiency also led to smaller hypopharyngeal glands. Bee brains contained high omega-3 concentrations, which were only slightly affected by diet, suggesting additional peripheral effects on learning. The shift from a low to high omega-6:3 ratio in the Western human diet is deemed a primary cause of many diseases and reduced mental health. A similar shift seems to be occurring in bee forage, possibly an important factor in colony declines. Our study shows the detrimental effect on cognitive performance of omega-3 deficiency in a nonmammal.Omega-3 and omega-6 fatty acids are two families of polyunsaturated fatty acids (PUFAs). Fatty acids (FAs) are important in structuring membrane lipids, and, because these PUFAs cannot be synthesized by higher animals, they must be acquired in the diet (1). Alpha-linolenic acid (ALA) (C18:3n-3) and linoleic acid (LA) (C18:2n-6) are the major omega-3 and omega-6 FAs, respectively. ALA is found in seeds, oils, and pollen. Some fish and other sea life also contain longer chain omega-3 FAs, eicosapentaenoic acid (EPA) (C20:5n-3) and docosahexaenoic acid (DHA) (C22:6n-3). Long-chain omega-3 PUFAs are major constituents of mammalian brain, and deficiency in these PUFAs, coupled with a high omega-6:3 ratio, is associated with many diseases and neurological disorders (2, 3). Because long-chain PUFAs occur in very low concentrations in insects (4), and Drosophila have been found to lack the necessary enzymes to synthesize them (5), insects have not been considered good models for studying the effect of omega-3 deficiency on cognitive performance. Nevertheless, a few studies have addressed this issue in insects, mainly in Drosophila, concluding that, although human and fly brain differ in long-chain FAs, lipids and lipid signaling are to a large extent conserved and important for the neuronal health of Drosophila (6).Bees provide crucial pollination services that support our food security, enrich our diet’s nutritional value, and are highly valued economically (7). These services are threatened worldwide by declining populations of pollinators, including the all-important honey bee. Malnutrition is emerging as one of the leading suspected culprits for declining bee populations, and for the plight of the honey bee in particular (7–10). Bees require nectar, their main carbohydrate source, and pollen, which provides proteins, lipids, vitamins, and minerals (11). Malnutrition may be due to low pollen quantity, quality, or diversity, a condition that is aggravated in agricultural monocultures (12–14), and in greenhouses (15). Malnourished bees have smaller hypopharyngeal glands (HPGs) (a source of queen and worker jelly) (9, 16), are more susceptible to deformed wing virus (16), are less tolerant to parasitism by Nosema ceranae (9), are more vulnerable to pesticides (17), have a compromised immune system (18), and have a shorter lifespan (19). Whereas diet quality is affected by amino acid content and composition, proteins alone cannot explain some of the effects of diet on bee health and colony functioning and deficits in additional nutritional factors: specifically, lipids are suspected (9). ALA and LA are generally considered essential fatty acids (eFAs) for most insects (20, 21), including bees (22).Pollens of different plant species vary greatly in lipid concentration and in the composition of FAs, including ALA and LA (23). In a diverse habitat, colonies tend to collect pollen from a variety of sources (24). But in disturbed habitats and extensive agricultural monocultures, the breadth of the diet is reduced (25), and bees may suffer from a deficiency of eFAs. Proper functioning of a honey bee colony relies on adequate production of young bees and on integration of many behaviors requiring sophisticated cognitive abilities.In the present study, we tested the effect of omega-3 dietary deficiency on the development of honey bee HPG and on the performance of bees in olfactory and tactile learning. Colonies were fed one of four artificial diets, two rich in omega-3 and two poor in omega-3. We found that omega-3–poor diets mainly reduced omega-3 levels in the body, and only slightly in the brain, and reduced HPG size. Omega-3 dietary deficiency greatly reduced performance in both olfactory and tactile associative learning assays. Our results show the influence of dietary omega-3 on cognitive performance in a model insect. Furthermore, we show a low omega-6:3 ratio of many wild flowers and of pollen collected by honey bee colonies, but a higher omega-6:3 ratio of some increasingly dominant cultivated plants, specifically almond and Eucalyptus. In a Petri dish experiment, olfactory associative learning of bees fed 1 wk on Eucalyptus pollen was greatly reduced. The reduction in omega-3 in modern human diet is deemed the most important global factor responsible for increased incidence of disease (2, 26). Likewise, our findings suggest that omega-3 deficits in bee nutrition, due to the limited diversity of pollen availability in transformed landscapes, may play a major role in decreased bee health and colony collapse disorder (CCD).     

The Association between Marine n-3 Polyunsaturated Fatty Acid Levels and Survival after Renal Transplantation

Background and objectives

Several studies have reported beneficial cardiovascular effects of marine n-3 polyunsaturated fatty acids. To date, no large studies have investigated the potential benefits of marine n-3 polyunsaturated fatty acids in recipients of renal transplants.

Design, setting, participants, & measurements

In this observational cohort study of 1990 Norwegian recipients of renal transplants transplanted between 1999 and 2011, associations between marine n-3 polyunsaturated fatty acid levels and mortality were investigated by stratified analysis and multivariable Cox proportional hazard regression analysis adjusting for traditional and transplant-specific mortality risk factors. Marine n-3 polyunsaturated fatty acid levels in plasma phospholipids were measured by gas chromatography in a stable phase 10 weeks after transplantation.

Results

There were 406 deaths (20.4%) during a median follow-up period of 6.8 years. Mortality rates were lower in patients with high marine n-3 polyunsaturated fatty acid levels (≥7.95 weight percentage) compared with low levels (<7.95 weight percentage) for all age categories (pooled mortality rate ratio estimate, 0.69; 95% confidence interval, 0.57 to 0.85). When divided into quartiles according to marine n-3 polyunsaturated fatty acid levels, patients in the upper quartile compared with the lower quartile had a 56% lower risk of death (adjusted hazard ratio, 0.44; 95% confidence interval, 0.26 to 0.75) using multivariable Cox proportional hazard regression analysis. There was a lower hazard ratio for death from cardiovascular disease with high levels of marine n-3 polyunsaturated fatty acid and a lower hazard ratio for death from infectious disease with high levels of the marine n-3 polyunsaturated fatty acid eicosapentaenoic acid, whereas there was no association between total or individual marine n-3 polyunsaturated fatty acid levels and cancer mortality.

Conclusions

Higher plasma phospholipid marine n-3 polyunsaturated fatty acid levels were independently associated with better patient survival.     

Committed carbon emissions, deforestation, and community land conversion from oil palm plantation expansion in West Kalimantan, Indonesia

Industrial agricultural plantations are a rapidly increasing yet largely unmeasured source of tropical land cover change. Here, we evaluate impacts of oil palm plantation development on land cover, carbon flux, and agrarian community lands in West Kalimantan, Indonesian Borneo. With a spatially explicit land change/carbon bookkeeping model, parameterized using high-resolution satellite time series and informed by socioeconomic surveys, we assess previous and project future plantation expansion under five scenarios. Although fire was the primary proximate cause of 1989-2008 deforestation (93%) and net carbon emissions (69%), by 2007-2008, oil palm directly caused 27% of total and 40% of peatland deforestation. Plantation land sources exhibited distinctive temporal dynamics, comprising 81% forests on mineral soils (1994-2001), shifting to 69% peatlands (2008-2011). Plantation leases reveal vast development potential. In 2008, leases spanned ～65% of the region, including 62% on peatlands and 59% of community-managed lands, yet <10% of lease area was planted. Projecting business as usual (BAU), by 2020 ～40% of regional and 35% of community lands are cleared for oil palm, generating 26% of net carbon emissions. Intact forest cover declines to 4%, and the proportion of emissions sourced from peatlands increases 38%. Prohibiting intact and logged forest and peatland conversion to oil palm reduces emissions only 4% below BAU, because of continued uncontrolled fire. Protecting logged forests achieves greater carbon emissions reductions (21%) than protecting intact forests alone (9%) and is critical for mitigating carbon emissions. Extensive allocated leases constrain land management options, requiring trade-offs among oil palm production, carbon emissions mitigation, and maintaining community landholdings.     

De novo production of the plant-derived alkaloid strictosidine in yeast

The monoterpene indole alkaloids are a large group of plant-derived specialized metabolites, many of which have valuable pharmaceutical or biological activity. There are ∼3,000 monoterpene indole alkaloids produced by thousands of plant species in numerous families. The diverse chemical structures found in this metabolite class originate from strictosidine, which is the last common biosynthetic intermediate for all monoterpene indole alkaloid enzymatic pathways. Reconstitution of biosynthetic pathways in a heterologous host is a promising strategy for rapid and inexpensive production of complex molecules that are found in plants. Here, we demonstrate how strictosidine can be produced de novo in a Saccharomyces cerevisiae host from 14 known monoterpene indole alkaloid pathway genes, along with an additional seven genes and three gene deletions that enhance secondary metabolism. This system provides an important resource for developing the production of more complex plant-derived alkaloids, engineering of nonnatural derivatives, identification of bottlenecks in monoterpene indole alkaloid biosynthesis, and discovery of new pathway genes in a convenient yeast host.Monoterpene indole alkaloids (MIAs) are a diverse family of complex nitrogen-containing plant-derived metabolites (1, 2). This metabolite class is found in thousands of plant species from the Apocynaceae, Loganiaceae, Rubiaceae, Icacinaceae, Nyssaceae, and Alangiaceae plant families (2, 3). Many MIAs and MIA derivatives have medicinal properties; for example, vinblastine, vincristine, and vinflunine are approved anticancer therapeutics (4, 5). These structurally complex compounds can be difficult to chemically synthesize (6, 7). Consequently, industrial production relies on extraction from the plant, but these compounds are often produced in small quantities as complex mixtures, making isolation challenging, laborious, and expensive (8–10). Reconstitution of plant pathways in microbial hosts is proving to be a promising approach to access plant-derived compounds as evidenced by the successful production of terpenes, flavonoids, and benzylisoquinoline alkaloids in microorganisms (11–19). Microbial hosts can also be used to construct hybrid biosynthetic pathways to generate modified natural products with potentially enhanced bioactivities (8, 20, 21). Across numerous plant species, strictosidine is believed to be the core scaffold from which all 3,000 known MIAs are derived (1, 2). Strictosidine undergoes a variety of redox reactions and rearrangements to form the thousands of compounds that comprise the MIA natural product family (Fig. 1) (1, 2). Due to the importance of strictosidine, the last common biosynthetic intermediate for all known MIAs, we chose to focus on heterologous production of this complex molecule (1). Therefore, strictosidine reconstitution represents the necessary first step for heterologous production of high-value MIAs.Open in a separate windowFig. 1.Strictosidine, the central intermediate in monoterpene indole alkaloid (MIA) biosynthesis, undergoes a series of reactions to produce over 3,000 known MIAs such as vincristine, quinine, and strychnine.     

Chloroplast acetyl-CoA carboxylase activity is 2-oxoglutarate–regulated by interaction of PII with the biotin carboxyl carrier subunit

The PII protein is a signal integrator involved in the regulation of nitrogen metabolism in bacteria and plants. Upon sensing of cellular carbon and energy availability, PII conveys the signal by interacting with target proteins, thereby modulating their biological activity. Plant PII is located to plastids; therefore, to identify new PII target proteins, PII-affinity chromatography of soluble extracts from Arabidopsis leaf chloroplasts was performed. Several proteins were retained only when Mg-ATP was present in the binding medium and they were specifically released from the resin by application of a 2-oxoglutarate-containing elution buffer. Mass spectroscopy of SDS/PAGE-resolved protein bands identified the biotin carboxyl carrier protein subunits of the plastidial acetyl-CoA carboxylase (ACCase) and three other proteins containing a similar biotin/lipoyl-binding motif as putative PII targets. ACCase is a key enzyme initiating the synthesis of fatty acids in plastids. In in vitro reconstituted assays supplemented with exogenous ATP, recombinant Arabidopsis PII inhibited chloroplastic ACCase activity, and this was completely reversed in the presence of 2-oxoglutarate, pyruvate, or oxaloacetate. The inhibitory effect was PII-dose-dependent and appeared to be PII-specific because ACCase activity was not altered in the presence of other tested proteins. PII decreased the V_max of the ACCase reaction without altering the K_m for acetyl-CoA. These data show that PII function has evolved between bacterial and plant systems to control the carbon metabolism pathway of fatty acid synthesis in plastids.