Burkholderia bacteria infectiously induce the proto-farming symbiosis of Dictyostelium amoebae and food bacteria

Symbiotic associations can allow an organism to acquire novel traits by accessing the genetic repertoire of its partner. In the Dictyostelium discoideum farming symbiosis, certain amoebas (termed “farmers”) stably associate with bacterial partners. Farmers can suffer a reproductive cost but also gain beneficial capabilities, such as carriage of bacterial food (proto-farming) and defense against competitors. Farming status previously has been attributed to amoeba genotype, but the role of bacterial partners in its induction has not been examined. Here, we explore the role of bacterial associates in the initiation, maintenance, and phenotypic effects of the farming symbiosis. We demonstrate that two clades of farmer-associated Burkholderia isolates colonize D. discoideum nonfarmers and infectiously endow them with farmer-like characteristics, indicating that Burkholderia symbionts are a major driver of the farming phenomenon. Under food-rich conditions, Burkholderia-colonized amoebas produce fewer spores than uncolonized counterparts, with the severity of this reduction being dependent on the Burkholderia colonizer. However, the induction of food carriage by Burkholderia colonization may be considered a conditionally adaptive trait because it can confer an advantage to the amoeba host when grown in food-limiting conditions. We observed Burkholderia inside and outside colonized D. discoideum spores after fruiting body formation; this observation, together with the ability of Burkholderia to colonize new amoebas, suggests a mixed mode of symbiont transmission. These results change our understanding of the D. discoideum farming symbiosis by establishing that the bacterial partner, Burkholderia, is an important causative agent of the farming phenomenon.Symbiotic interactions are ubiquitous in nature and can play a central role in the evolutionary trajectory of organisms. For instance, symbiosis can drive rapid lateral procurement of novel traits as interacting organisms gain access to the genetic capabilities of their partner (1, 2). The evolutionary power of symbiosis is apparent in the many major life forms that owe their very existence to past and present symbiotic partnerships (3, 4). A famous example is the emergence of eukaryotes through their ancestor’s acquisition of bacteria that subsequently evolved into organelles indispensable for energy generation (5). Although many classic examples of symbiosis are conspicuously mutualistic, the characteristics of other symbiotic associations can be complex, dynamic, and less definable. In some cases, symbionts have good or bad effects on their host that vary depending on genotypic and environmental details (6, 7). The length and transmission mode of symbiosis also can have strong effects on the selection and evolution of partner traits. Although older symbiotic associations are often obligate and stable, recent associations can be transient and protean (8). Additionally, vertical transmission may favor mutualistic interactions, whereas horizontal transmission can allow the emergence and spread of more pathogenic characteristics (9–11). However, as a whole, the fates of symbioses are often the result of a delicate balance between mutualism and pathogenesis, requiring pathogenic characteristics at the least to facilitate infection and beneficial properties to promote maintenance (12, 13). Indeed, many cases of mutualistic associations are thought to have evolved from ancient parasitic infections (14, 15). Examining nascent, malleable, or less definable forms of symbiosis may provide insight into the mechanisms that promote or corrode this balance and their subsequent evolutionary consequences.Amoeba–bacteria interactions make a promising system for gaining insight into diverse and dynamic symbiotic relationships. Amoebas interact with bacteria in multiple ways. Most apparently, they are predators of bacteria. However, other amoeba–bacteria interactions are less favorable for the amoebas. Some bacteria can evade amoeba phagocytosis and thereby diminish amoeba predatory prowess and food acquisition (16). Still worse, amoebas can fall victim to bacterial processes or exploitation, with some bacteria producing products detrimental to amoeba fitness or surviving phagocytosis to invade and multiply within amoeba cells (17, 18). There also are stable symbiotic interactions between amoebas and bacteria in which the origins, mechanisms, and impacts on both species are less defined. For instance, several bacterial endosymbionts inhabit amoebas, incurring variable and not always obvious consequences to the amoeba host (19–22). In addition, certain isolates of the soil-dwelling amoeba Dictyostelium discoideum persistently associate with bacteria, an association that has beneficial or detrimental outcomes depending on the environmental conditions (23–25). Amoebas can serve as environmental reservoirs for bacterial pathogens (26, 27) or as training facilities for the adaptation of bacteria to evade eukaryotic phagocytosis or to survive intracellularly after phagocytosis (17, 28). Although, for the eukaryotic host, some of these interactions may have decidedly unfortunate outcomes, such as the emergence of bacterial pathogenesis through intracellular adaptation, others may illuminate important evolutionary advances, such as the transition of bacterial endosymbionts into organelles that provide novel functionality. Thus, the diversity and persistence of amoeba–bacteria interactions may have several ecological and health-related consequences.The stable association between bacteria and some wild isolates of D. discoideum supplies a particularly interesting study system for elucidating symbiotic causes and consequences. D. discoideum is a soil-dwelling amoeba that transitions between solitary and social life stages (29). In the solitary stage, D. discoideum cells consume bacteria through phagocytosis and divide by binary fission. When food is exhausted, amoebas coaggregate, ultimately forming a multicellular structure called a “fruiting body.” As the fruiting body develops, ∼20% of the cells sacrifice themselves to form an erect stalk. The remaining cells ascend the stalk, forming a globular sorus at the top where they differentiate into sturdy spores (29). In the sorus, spores are positioned for dispersal into more favorable environments, presumably through contact and transport upon animals (30). Multiple wild isolates of the amoeba D. discoideum, but not all of them, have been found to be stably associated with several bacteria species (24). These amoebas persistently carry both edible and inedible bacteria with them through the social stage and are termed “farmers” because of their ability to reseed new environments with a food source (23, 24). Interestingly, farmer isolates produce fewer spores under optimal conditions than their non–bacteria-carrying counterparts; however, this cost is countered by farmers’ advantage in being able to replenish their food supply when dispersing to food-poor environments (24). Additionally, some of the bacterial isolates that farmers carry produce compounds detrimental to nonfarmer clones but not to their host farmer, giving the host farmer a competitive advantage in a mixed population (23, 25).The ease of D. discoideum manipulation coupled with the variability inherent in the farming symbiosis provide a promising platform for addressing questions concerning symbiosis between microbes and eukaryotes. For instance, are mutualistic associations and their resulting phenotypes driven by the host, by the bacteria, or by a very specific interaction between the two? How much coevolution is required to reach a beneficial outcome? In aphids and other insects, defensive symbionts can sweep through populations and be horizontally transferred to new hosts (31, 32). Even Buchnera, a vertically transferred obligate symbiont of aphids, still confers its benefits to new hosts after experimental infection (33). Taken together, this horizontal transfer suggests that little coevolution may be needed for the formation of novel symbiosis. However, in some plant–rhizobia or –mycorrhizal associations, the symbiont phenotype can vary substantially among hosts, and the outcome of the association is determined by the interaction of host and symbiont-derived factors (34–38). Similarly, a synergistic interplay between host and symbiont components mediates the initiation and persistence of the bobtail squid–Vibrio fischeri symbiosis (39–41). For the D. discoideum farming symbiosis, it previously had been assumed that farmers were genetically distinct from nonfarmers, suggesting the role of a host-specific factor in establishing the symbiosis (24). This study aims to characterize more thoroughly the partner dynamics within the D. discoideum farming symbiosis by specifically analyzing the role of bacterial associates in farming phenotypes.To determine the role bacterial partners play in farming, we first examined the diversity of bacterial passengers associated with our present collection of stable farmer clones. We confirmed that several different bacterial species can be isolated from farmer D. discoideum; however isolates belonging to the Burkholderia genus were ubiquitous among our tested farmers. These Burkholderia isolates fail to support amoeba growth when provided as the only food source and therefore are considered inedible. Because of their prevalence in our farmer clones and because Burkholderia species form symbiotic relationships with diverse organisms, we hypothesized that these Burkholderia isolates could be crucial for the symbiotic relationship with D. discoideum that results in the farming phenomenon (42). Therefore we asked whether nonfarmer D. discoideum could be colonized by farmer-associated Burkholderia isolates and whether colonization could induce secondary bacterial carriage. We established that the Burkholderia associated with D. discoideum fall into two distinct phylogenetic clades. We found that the tested Burkholderia isolates from each clade robustly colonized nonfarmer D. discoideum sori, with this colonization persisting through multiple rounds of D. discoideum spore dispersal, germination, and vegetative growth. Like their farmer counterparts, nonfarmers colonized with Burkholderia can carry bacterial food, allowing them to reseed new territories with food bacteria following spore dispersal. Inversely, removal of Burkholderia from wild farmers by antibiotic treatment results in the loss of detectable bacterial food carrying. These findings suggest that Burkholderia colonization drives secondary bacterial carriage (farming) in D. discoideum. In total, these results suggest that specific Burkholderia isolates stably colonize D. discoideum and induce a novel adaptive trait of ecological relevance, the carriage of bacterial food. Our initial evidence suggests that the consequences of Burkholderia carriage may differ according to symbiont and host genotypes. For instance, some Burkholderia isolates impose a higher cost to their hosts, and the extent of this cost appears to be more severe for newer hosts than for the original host. We also observe Burkholderia (and occasionally, our laboratory food bacterium, Klebsiella pneumoniae) inside colonized D. discoideum spores after fruiting body formation. This observation, together with Burkholderia’s ability to be horizontally transmitted to new hosts and to associate stably with old hosts, suggests a mixed mode of Burkholderia transmission. The less severe fitness costs exerted by Burkholderia colonization in the original hosts suggests that long-term vertical transmission may lead to compensatory host adaptation.     

Disruption of Renal Tubular Mitochondrial Quality Control by Myo-Inositol Oxygenase in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is associated with oxidative stress and mitochondrial injury. Myo-inositol oxygenase (MIOX), a tubular-specific enzyme, modulates redox imbalance and apoptosis in tubular cells in diabetes, but these mechanisms remain unclear. We investigated the role of MIOX in perturbation of mitochondrial quality control, including mitochondrial dynamics and autophagy/mitophagy, under high-glucose (HG) ambience or a diabetic state. HK-2 or LLC-PK1 cells subjected to HG exhibited an upregulation of MIOX accompanied by mitochondrial fragmentation and depolarization, inhibition of autophagy/mitophagy, and altered expression of mitochondrial dynamic and mitophagic proteins. Furthermore, dysfunctional mitochondria accumulated in the cytoplasm, which coincided with increased reactive oxygen species generation, Bax activation, cytochrome C release, and apoptosis. Overexpression of MIOX in LLC-PK1 cells enhanced the effects of HG, whereas MIOX siRNA or d-glucarate, an inhibitor of MIOX, partially reversed these perturbations. Moreover, decreasing the expression of MIOX under HG ambience increased PTEN-induced putative kinase 1 expression and the dependent mitofusin-2–Parkin interaction. In tubules of diabetic mice, increased MIOX expression and mitochondrial fragmentation and defective autophagy were observed. Dietary supplementation of d-glucarate in diabetic mice decreased MIOX expression, attenuated tubular damage, and improved renal functions. Notably, d-glucarate administration also partially attenuated mitochondrial fragmentation, oxidative stress, and apoptosis and restored autophagy/mitophagy in the tubular cells of these mice. These results suggest a novel mechanism linking MIOX to impaired mitochondrial quality control during tubular injury in the pathogenesis of DKD and suggest d-glucarate as a potential therapeutic agent for the amelioration of DKD.     

Intraoperative transfusion-related acute lung injury in a child during calvarial vault remodeling

Transfusion-related acute lung injury (TRALI) is currently recognized by the US Food and Drug Administration as the number one cause of mortality related to blood transfusion. Although various pathophysiologic mechanisms have been proposed, it is thought to be related to the presence of anti-HLA antibodies or bioactive lipid components in the donor blood product, which results in activation of recipient leukocytes and the resultant pulmonary damage from the release of bioactive substances including cytokines. As TRALI manifests as acute lung injury with signs and symptoms consistent with acute respiratory distress syndrome, it is frequently underdiagnosed, as the acute lung injury may be attributed to other factors. Transfusion-related acute lung injury is an important clinical entity for anesthesia providers to recognize and diagnose accurately, as many transfusions occur in the surgical patient. We present a case report of a pediatric patient who developed intraoperative TRALI during calvarial vault remodeling to treat craniosynostosis. The history, pathophysiology, and treatment of TRALI are discussed. Potential preventive measures are reviewed.     

Early composite cranioplasty in infants with severe aplasia cutis congenita: a report of two cases.

OBJECTIVE: Severe cutis aplasia congenita has traditionally been treated with initial soft tissue coverage and delayed cranioplasty. We advocate the technique of early composite reconstruction of both bone and soft tissues. METHODS: Two cases of cutis aplasia congenita with large skull defects (6 x 10 cm, 8 x 8 cm) of superficial layers, skull, and dura are presented. In each case, composite reconstruction was undertaken before 2 weeks of age with restoration of bony and soft tissue coverage through autologous, full-thickness cranial bone grafts and scalp flaps. Both children have been followed up over 2 years with clinical examination and computed tomography (CT) scans. RESULTS: In both cases, defects were completely repaired postoperatively and remained closed 2 years later. Complete regeneration of calvarial bone graft donor sites were documented by CT scan. Head shape and circumference were normal at 2-year follow up.     

Massive repeated nose bleeding after bimaxillary osteotomy

In LeFort I surgery, the separation of the pterygomaxillary junction is done by osteotomy. Although the osteotome is positioned too close to the maxillary artery and its branches during pterygomaxillary separation, postoperative complications from vascular injuries are uncommon. We describe an unusual occurrence of a maxillary artery pseudoaneurysm after LeFort I and bilateral sagittal split osteotomies for maxillary advancement and mandibular setback as well as (anterior sliding) genioplasty. In a patient with class III occlusion and midface retrusion, the significant bleeding began 10 days postoperatively, which was controlled by anterior and posterior nasal packing. The bleeding recurred 28 days after surgery; thus, vascular anatomy in the pterygomaxillary area is reviewed, pseudoaneurysm was diagnosed on selective carotid angiography and successfully treated by embolization; and 2-year follow up was uneventful.     

The Effect of Type of Femoral Component Fixation on Mortality and Morbidity after Hip Hemiarthroplasty: A Systematic Review and Meta-Analysis

HSS Journal ® - Hip hemiarthroplasty is a well-established treatment of displaced femoral neck fracture, although debate exists over whether cemented or uncemented fixation is superior....     

Utility of Autopsy among Pediatric Allogeneic Hematopoietic Stem Cell Transplant Recipients: One Last Chance to Learn?

Autopsy may confirm clinical diagnoses or identify conditions that were not suspected prior to a patient's death. Previous studies evaluating the utility of autopsy in hematopoietic stem cell transplant (HSCT) recipients yielded conflicting results.We conducted a retrospective cohort study of children (<18 years of age) undergoing allogeneic HSCT at Duke University who died of any cause between January 1, 1995, and December 31, 2016. We evaluated associations between patient characteristics and autopsy performance using chi-square or Fisher exact tests. We reviewed autopsy reports to determine the concordance between preautopsy causes of death and pathological diagnoses identified on autopsy. We classified unexpected diagnoses on autopsy using criteria developed by Goldman et al. We evaluated for temporal changes in the autopsy consent rate and the frequency of unexpected diagnoses on autopsy using Cochran-Armitage tests.During the 22-year study period, 475 patients died and had data available on autopsy performance, and 130 (27%) of these patients underwent autopsy. The autopsy consent rate declined over time (P < .0001), with autopsies being performed for 40% of deaths in 1995 to 1999 and 17% of deaths in 2009 to 2016. White patients were more likely to undergo autopsy than nonwhite patients (P?=?.03). There were no associations between autopsy performance and patient age, sex, HSCT indication, or HSCT donor. Unexpected diagnoses were identified in 31 (24%) autopsies. The proportion of autopsies with an unexpected diagnosis did not change during the study period (P?=?.45). However, infectious diagnoses that would have led to a change in management were more frequently identified on autopsies in 1995 to 2003 than in 2004 to 2016 (20% versus 0%; P?=?.001).The autopsy consent rate for pediatric HSCT recipients at our institution has declined substantially over the past several decades. The utility of autopsy in this patient population remains high despite a reduction in the identification of unexpected infections.     

Isolated metastatic myocardial carcinoid tumor in a 48-year-old man

This brief report describes an asymptomatic patient with a myocardial mass. Two-dimensional echocardiography, technetium Tc 99m cardiac nuclear scan, and transesophageal echocardiography were performed to define the mass. The mass, which involved the subvalvar right ventricular free wall, was resected and determined to be a metastatic carcinoid tumor by histologic and immunohistochemical analysis. Further investigation revealed the presence of a midgut carcinoid tumor located within the terminal ileum, which was also resected surgically. The patient recovered well after surgery and adjunctive chemotherapy. To our knowledge, this is the first report of comprehensive nuclear and echocardiographic imaging, supplemented by surgical and pathologic findings, in an asymptomatic patient with isolated myocardial metastasis of an ileal carcinoid tumor.