Biological impact on mineral dissolution: application of the lichen model to understanding mineral weathering in the rhizosphere

Microorganisms modify rates and mechanisms of chemical and physical weathering and clay growth, thus playing fundamental roles in soil and sediment formation. Because processes in soils are inherently complex and difficult to study, we employ a model based on the lichen-mineral system to identify the fundamental interactions. Fixed carbon released by the photosynthetic symbiont stimulates growth of fungi and other microorganisms. These microorganisms directly or indirectly induce mineral disaggregation, hydration, dissolution, and secondary mineral formation. Model polysaccharides were used to investigate direct mediation of mineral surface reactions by extracellular polymers. Polysaccharides can suppress or enhance rates of chemical weathering by up to three orders of magnitude, depending on the pH, mineral surface structure and composition, and organic functional groups. Mg, Mn, Fe, Al, and Si are redistributed into clays that strongly adsorb ions. Microbes contribute to dissolution of insoluble secondary phosphates, possibly via release of organic acids. These reactions significantly impact soil fertility. Below fungi-mineral interfaces, mineral surfaces are exposed to dissolved metabolic byproducts. Through this indirect process, microorganisms can accelerate mineral dissolution, leading to enhanced porosity and permeability and colonization by microbial communities.     

Regulation of the vasculature: clues from lupus

Blood vessel homeostasis involves a complex interplay between inflammatory signals, hormones, and other mediators. Recent research suggests that although atherosclerosis is primarily a problem of impaired lipid regulation, the very processes of cholesterol and triglyceride metabolism are intrinsically tied to inflammatory and hormonal regulatory signals. Similarities between inflammatory and endocrine disturbances in systemic lupus and the predicted consequences for vascular regulation help explain the high incidence of premature atherosclerosis in lupus. Atherosclerosis in systemic lupus, then, may be a consequence of imbalances in what are intrinsic homeostatic mechanisms, rather than a result of externally superimposed pathologic changes.     

Future treatments for diabetic neuropathy: clues from experimental neuropathy

Neuropathy remains a major complication of diabetes and there is no approved treatment that prevents its progression or alleviates the associated symptoms. Animal models of diabetic neuropathy are hampered by their short life span, which precludes the development of overt structural pathology, and they are best viewed as exhibiting early metabolic, neurochemical, and functional indices of nerve disorders that may predict progression to overt diabetic neuropathy. In this context, diabetic animals have use in both establishing potential etiologic mechanisms and for screening novel therapeutic agents. Treatment strategies are evolving in concert with a developing understanding of how hyperglycemia causes nerve dysfunction and recent or ongoing clinical trials are investigating this rational approach to drug design. It is only by the successful demonstration of clinical efficacy of a compound developed by this approach that the use of animal models of diabetic neuropathy can be validated.     

Pancreatic disorders in children: New clues on the horizon

Pancreatic disorders in children represent a growing health problem in pediatric patients. In the past two decades, several advances have been made in the knowledge of pediatric pancreatic disorders, with better understanding of different etiologies and clinical manifestations of these disorders. Moreover, many efforts have been made in pancreatology, aiming to define guidelines in the management of pancreatitis in children, initially based on the available information in adults. A multidisciplinary and multicenter approach is necessary to better determine pancreatic disease pathways and treatment options in children.     

Complexity of attrition in the treatment of obesity: clues from a structured telephone interview

OBJECTIVES: To investigate the causes of attrition reported by obese patients treated by medical centres. DESIGN: Observational study. SETTING: Obese patients enrolled in a long-term study involving 18 Italian medical centres. PARTICIPANTS: A total of 940 obese patients (727 female; mean age, 49 years; mean BMI, 38.6 kg/m2). MEASUREMENTS: Causes of attrition reported by dropouts during a structured telephone interview. RESULTS: After a median observation period of 41 months (range, 25-50), 766 of 940 patients (81.5%) discontinued treatment. Sixty-two per cent of total dropout occurred in the first year of follow-up. Seventy-four per cent of dropouts reported a single primary reasons for treatment interruption. Two primary reasons were reported by 22.4% of patients, and three reasons by 3.4%. Practical difficulties, alone or in combination, were reported by more than half of dropouts (55%), and were the leading cause of attrition followed by perceived failure of treatment. Among practical difficulties, family problems or problems at work and logistics, coupled with health problems other than obesity, were the most frequent reasons of attrition, but also a perceived sense of abandonment or a bad interaction with therapists were frequently reported. CONCLUSION: Practical difficulties and psychological problems are the most important reasons of attrition reported by patients. A therapeutic alliance addressing these issues has a large potential to reduce treatment interruption and to improve outcome in obesity.     

Subunit interactions within the T-cell antigen receptor: clues from the study of partial complexes.

The T-cell antigen receptor is a multisubunit complex composed of seven transmembrane chains (alpha beta gamma delta epsilon zeta 2). Subunit interactions within this complex were defined by analyzing the subunit composition of partial complexes. These partial complexes were observed in mutant and tumor T cells that fail to synthesize one or more of the receptor chains or in fibroblasts transfected with genes encoding T-cell antigen receptor chains. In addition, partial complexes were generated by immunoprecipitation with antibodies that cause selective dissociation of T-cell antigen receptor chains. The alpha and beta chains were found to form a disulfide-linked dimer in the absence of any of the other chains. The gamma, delta, and epsilon chains were also efficiently associated in the absence of a complete heterodimer. Complexes composed only of delta epsilon or gamma epsilon could be observed. Both these dimers, as well as the gamma delta epsilon trimer, could form stable complexes with alpha beta, even in the absence of zeta 2. The zeta 2 dimer could bind directly to alpha beta. In the absence of a complete clonotypic heterodimer, zeta 2 was not stably associated with gamma delta epsilon. These observations suggest a model in which alpha beta interacts directly with the gamma delta epsilon trimer and zeta 2, with less-direct interaction between the latter two.     

Methanol incorporation in clathrate hydrates and the implications for oil and gas pipeline flow assurance and icy planetary bodies

One of the best-known uses of methanol is as antifreeze. Methanol is used in large quantities in industrial applications to prevent methane clathrate hydrate blockages from forming in oil and gas pipelines. Methanol is also assigned a major role as antifreeze in giving icy planetary bodies (e.g., Titan) a liquid subsurface ocean and/or an atmosphere containing significant quantities of methane. In this work, we reveal a previously unverified role for methanol as a guest in clathrate hydrate cages. X-ray diffraction (XRD) and NMR experiments showed that at temperatures near 273 K, methanol is incorporated in the hydrate lattice along with other guest molecules. The amount of included methanol depends on the preparative method used. For instance, single-crystal XRD shows that at low temperatures, the methanol molecules are hydrogen-bonded in 4.4% of the small cages of tetrahydrofuran cubic structure II hydrate. At higher temperatures, NMR spectroscopy reveals a number of methanol species incorporated in hydrocarbon hydrate lattices. At temperatures characteristic of icy planetary bodies, vapor deposits of methanol, water, and methane or xenon show that the presence of methanol accelerates hydrate formation on annealing and that there is unusually complex phase behavior as revealed by powder XRD and NMR spectroscopy. The presence of cubic structure I hydrate was confirmed and a unique hydrate phase was postulated to account for the data. Molecular dynamics calculations confirmed the possibility of methanol incorporation into the hydrate lattice and show that methanol can favorably replace a number of methane guests.     

Epidemiology: clues to the pathogenesis of Burkitt lymphoma

The two major epidemiological clues to the pathogenesis of Burkitt lymphoma (BL) are the geographical association with malaria--BL incidence relates to the malaria transmission rate--and early infection by Epstein-Barr virus (EBV). Both agents cause B cell hyperplasia, which is almost certainly an essential component of lymphomagenesis in BL. The critical event in lymphomagenesis is the creation of a MYC translocation, bringing the MYC gene into juxtaposition with immunoglobulin genes and causing its ectopic expression, thereby driving the proliferation of BL cells. It is highly likely that such translocations are mediated by the activation-induced cytidine deaminase (AID) gene, which is responsible for hypervariable region mutations as well as class switching. Stimulation of the Toll-like receptor 9 by malaria-associated agonists induces AID, providing a mechanism whereby malaria could directly influence BL pathogenesis. EBV-containing cells must reach the memory cell compartment in order to survive throughout the life of the individual, which probably requires traversal of the germinal centre. Normally, cells that do not produce high affinity antibodies do not survive this passage, and are induced to undergo apoptosis. EBV, however, prevents this, and in doing so may also enhance the likelihood of survival of rare translocation-containing cells.     

Early evolution of photosynthesis: clues from nitrogenase and chlorophyll iron proteins.

Chlorophyll (Chl) is often viewed as having preceded bacteriochlorophyll (BChl) as the primary photoreceptor pigment in early photosynthetic systems because synthesis of Chl requires one fewer enzymatic reduction than does synthesis of BChl. We have conducted statistical DNA sequence analyses of the two reductases involved in Chl and BChl synthesis, protochlorophyllide reductase and chlorin reductase. Both are three-subunit enzymes in which each subunit from one reductase shares significant amino acid identity with a subunit of the other, indicating that the two enzymes are derived from a common three-subunit ancestral reductase. The "chlorophyll iron protein" subunits, encoded by the bchL and bchX genes in the purple bacterium Rhodobacter capsulatus, also share amino acid sequence identity with the nitrogenase iron protein, encoded by nifH. When nitrogenase iron proteins are used as outgroups, the chlorophyll iron protein tree is rooted on the chlorine reductase lineage. This rooting suggests that the last common ancestor of all extant photosynthetic eubacteria contained BChl, not Chl, in its reaction center, and implies that Chl-containing reaction centers were a late invention unique to the cyanobacteria/chloroplast lineage.     

From the Cover: Volcanic history of the Imbrium basin: A close-up view from the lunar rover Yutu

We report the surface exploration by the lunar rover Yutu that landed on the young lava flow in the northeastern part of the Mare Imbrium, which is the largest basin on the nearside of the Moon and is filled with several basalt units estimated to date from 3.5 to 2.0 Ga. The onboard lunar penetrating radar conducted a 114-m-long profile, which measured a thickness of ∼5 m of the lunar regolith layer and detected three underlying basalt units at depths of 195, 215, and 345 m. The radar measurements suggest underestimation of the global lunar regolith thickness by other methods and reveal a vast volume of the last volcano eruption. The in situ spectral reflectance and elemental analysis of the lunar soil at the landing site suggest that the young basalt could be derived from an ilmenite-rich mantle reservoir and then assimilated by 10–20% of the last residual melt of the lunar magma ocean.The surface of the Moon is covered by regolith, a mixed layer of fine-grained lunar soil and ejecta deposits, which is crucial to understanding the global composition of the Moon. The lunar regolith has also recorded the complex history of the surface processes, and it is the main reservoir of ³He and other solar wind gases. The thickness of the lunar regolith was estimated to be from 2 to 8 m in the maria and up to 8–16 m in the highland areas using various methods (1), including crater morphology (2, 3), seismology with low spatial resolution (4), radar wave scattering (5), and microwave brightness temperature (6). However, no in situ measurement of spectral reflectance, elemental compositions, lunar regolith thickness, or subsurface structures has been carried out.The surface of the Moon is dominated with numerous large basins. They were formed about 3.9 Ga (7, 8), probably by the late heavy bombardment, and then filled with dark lava flows derived from partial melting of the lunar mantle, within a period mainly during 3.8–3.1 Ga (7). The Imbrium basin is the largest and was formed on Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane (9), a unique terrain highly enriched in U, Th, and K radionuclides and other incompatible trace elements referred to as KREEP (10) and considered as the last residual melt of the Lunar Magma Ocean (11). The presence of the KREEPy materials, indicated by high concentrations of radionuclides U, Th, and K (9), around the rims of the Imbrium basin suggests that they are likely the basin-forming ejecta deposits. At least three main lava flows, dated from 3.5 Ga to 2.0–2.3 Ga (7, 12), have been recognized in Mare Imbrium with distinct FeO and TiO₂ concentrations (13, 14), which brought up interior information of this KREEP-rich terrain. The old and low-Ti basalt unit has been sampled by the Apollo 15 mission that landed at the eastern rim of the Imbrium basin. Information of other lava flows in Mare Imbrium was obtained only by remote sensing from orbit. On December 14, 2013, Chang’e-3 successfully landed on the young and high-Ti lava flow in the northeastern Mare Imbrium, about 10 km south from the old low-Ti basalt unit (Fig. 1).Open in a separate windowFig. 1.The landing site of Chang’e-3 (red cross), on the high-Ti basalt (dark gray) near the boundary in contact with the low-Ti basalt (light gray). The background image was taken by Chang’e-1.The lunar rover Yutu (named for the jade rabbit on the Moon in a Chinese fairy tale) was equipped with an active particle-induced X-ray spectrometer (APXS), a visible to near-infrared (450–945 nm) imaging spectrometer and short-wave infrared (900–2,395 nm) spectrometer (VNIS), and a lunar penetrating radar (LPR), accompanied by a stereo camera and a navigating camera. Originally, the mission planned to have the lunar rover measure chemical and mineral compositions of the lunar soil and various types of ejecta rocks and to carry out a LPR profile of the lunar regolith and subsurface structures in the first 3 mo. The mission was scheduled to extend up to 1 y and to explore the old low-Ti lava flow ∼10 km north. Unfortunately, some of Yutu’s mechanical parts failed to move just before the rover prepared for sleeping at the end of the second month due to unknown faults probably in the control system. During the first 2 mo, Yutu successfully carried out two APXS and four VNIS analyses of the lunar soil and performed a 114-m-long LPR profile along the rover track in the landing area (Fig. 2). These in situ measurements provide insights into the volcanic history of Mare Imbrium and the ground-truth data for calibration of the orbital data.Open in a separate windowFig. 2.Chang’e-3 landing site and the rover Yutu’s track. Crater A is blocky, indicating penetration through the regolith. Crater B is the largest one without blocks in the landing area. The APXS (LS1–LS2) and VNIS (CD5–CD8) analysis positions and the rover navigation points are marked. The image was composed from the series images taken by the Chang’e-3 landing camera.