Search

Honey bees have suffered dramatic losses in recent years, largely due to multiple stressors underpinned by poor nutrition [1]. Nutritional stress especially harms larvae, who mature into workers unable to meet the needs of their colony [2]. In this study, we characterize the metabolic capabilities of a honey bee larvae-associated bacterium, Bombella apis(formerly Parasaccharibacter apium), and its effects on the nutritional resilience of larvae. We found that B. apisis the only bacterium associated with larvae that can withstand the antimicrobial larval diet. Further, we found that B. apiscan synthesize all essential amino acids and significantly alters the amino acid content of synthetic larval diet, largely by supplying the essential amino acid lysine. Analyses of gene gain/loss across the phylogeny suggest that four amino acid transporters were gained in recent B. apisancestors. In addition, the transporter LysE is conserved across all sequenced strains of B. apis. Finally, we tested the impact of B. apison developing honey bee larvae subjected to nutritional stress and found that larvae supplemented with B. apisare bolstered against mass reduction despite limited nutrition. Together, these data suggest a novel role of B. apisas a nutritional mutualist of honey bee larvae.

Honey bees have suffered dramatic losses in recent years, largely due to multiple stressors underpinned by poor nutrition [1]. Nutritional stress especially harms larvae, who mature into workers unable to meet the needs of their colony [2]. In this study, we characterize the metabolic capabilities of a honey bee larvae-associated bacterium, Bombella apis(formerly Parasaccharibacter apium), and its effects on the nutritional resilience of larvae. We found that B. apisis the only bacterium associated with larvae that can withstand the antimicrobial larval diet. Further, we found that B. apiscan synthesize all essential amino acids and significantly alters the amino acid content of synthetic larval diet, largely by supplying the essential amino acid lysine. Analyses of gene gain/loss across the phylogeny suggest that four amino acid transporters were gained in recent B. apisancestors. In addition, the transporter LysE is conserved across all sequenced strains of B. apis. Finally, we tested the impact of B. apison developing honey bee larvae subjected to nutritional stress and found that larvae supplemented with B. apisare bolstered against mass reduction despite limited nutrition. Together, these data suggest a novel role of B. apisas a nutritional mutualist of honey bee larvae.

The fruit fly Drosophila melanogasterhas emerged as a powerful model for investigating the molecular mechanisms that regulate animal metabolism. However, a major limitation of these studies is that many metabolic assays are tedious, dedicated to analyzing a single molecule, and rely on indirect measurements. As a result, Drosophilageneticists commonly use candidate gene approaches, which, while important, bias studies toward known metabolic regulators. In an effort to expand the scope of Drosophilametabolic studies, we used the classic mutant lysine(lys) to demonstrate how a modern metabolomics approach can be used to conduct forward genetic studies. Using an inexpensive and well-established gas chromatography-mass spectrometry-based method, we genetically mapped and molecularly characterized lysby using free lysine levels as a phenotypic readout. Our efforts revealed that lysencodes the Drosophilahomolog of Lysine Ketoglutarate Reductase/Saccharopine Dehydrogenase, which is required for the enzymatic degradation of lysine. Furthermore, this approach also allowed us to simultaneously survey a large swathe of intermediate metabolism, thus demonstrating that Drosophilalysine catabolism is complex and capable of influencing seemingly unrelated metabolic pathways. Overall, our study highlights how a combination of Drosophilaforward genetics and metabolomics can be used for unbiased studies of animal metabolism, and demonstrates that a single enzymatic step is intricately connected to diverse aspects of metabolism.

L-2-hydroxyglutarate (L-2HG) is an oncometabolite found elevated in renal tumors. However, this molecule might have physiological roles that extend beyond its association with cancer, as L-2HG levels are elevated in response to hypoxia and during Drosophila larval development. L-2HG is known to be metabolized by L-2HG dehydrogenase (L2HGDH), and loss of L2HGDH leads to elevated L-2HG levels. Despite L2HGDH being highly expressed in the kidney, its role in renal metabolism has not been explored. Here, we report our findings utilizing a novel CRISPR/Cas9 murine knockout model, with a specific focus on the role of L2HGDH in the kidney. Histologically, L2hgdh knockout kidneys have no demonstrable histologic abnormalities. However, GC-MS metabolomics demonstrates significantly reduced levels of the TCA cycle intermediate succinate in multiple tissues. Isotope labeling studies with [U-13C] glucose demonstrate that restoration of L2HGDH in renal cancer cells (which lowers L-2HG) leads to enhanced incorporation of label into TCA cycle intermediates. Subsequent biochemical studies demonstrate that L-2HG can inhibit the TCA cycle enzyme α-ketoglutarate dehydrogenase. Bioinformatic analysis of mRNA expression data from renal tumors demonstrates that L2HGDH is co-expressed with genes encoding TCA cycle enzymes as well as the gene encoding the transcription factor PGC-1α, which is known to regulate mitochondrial metabolism. Restoration of PGC-1α in renal tumor cells results in increased L2HGDH expression with a concomitant reduction in L-2HG levels. Collectively, our analyses provide new insight into the physiological role of L2HGDH as well as mechanisms that promote L-2HG accumulation in disease states.

The enantiomers of 2-hydroxyglutarate (2HG) are potent regulators of metabolism, chromatin modifications and cell fate decisions. Although these compounds are associated with tumor metabolism and commonly referred to as oncometabolites, both D- and L-2HG are also synthesized by healthy cells and likely serve endogenous functions. The metabolic mechanisms that control 2HG metabolism in vivo are poorly understood. One clue towards how cells regulate 2HG levels has emerged from an inborn error of metabolism known as combined D- and L-2HG aciduria (D-/L-2HGA), which results in elevated D- and L-2HG accumulation. Because this disorder is caused by mutations in the mitochondrial citrate transporter (CIC), citrate must somehow govern 2HG metabolism in healthy cells. The mechanism linking citrate and 2HG, however, remains unknown. Here, we use the fruit fly Drosophila melanogaster to elucidate a metabolic link between citrate transport and L-2HG accumulation. Our study reveals that the Drosophila gene scheggia (sea), which encodes the fly CIC homolog, dampens glycolytic flux and restricts L-2HG accumulation. Moreover, we find that sea mutants accumulate excess L-2HG owing to elevated lactate production, which inhibits L-2HG degradation by interfering with L-2HG dehydrogenase activity. This unexpected result demonstrates that citrate indirectly regulates L-2HG stability and reveals a feedback mechanism that coordinates L-2HG metabolism with glycolysis and the tricarboxylic acid cycle. Finally, our study also suggests a potential strategy for preventing L-2HG accumulation in human patients with CIC deficiency. This article has an associated First Person interview with the first author of the paper.

The field of metabolic research has experienced an unexpected renaissance. While this renewed interest in metabolism largely originated in response to the global increase in diabetes and obesity, studies of metabolic regulation now represent the frontier of many biomedical fields. This trend is especially apparent in developmental biology, where metabolism influences processes ranging from stem cell differentiation and tissue growth to sexual maturation and reproduction. In this regard, the fruit fly Drosophila melanogasterhas emerged as a powerful tool for dissecting conserved mechanisms that underlie developmental metabolism, often with a level of detail that is simply not possible in other animals. Here we describe why the fly is an ideal system for exploring the relationship between metabolism and development, and outline a basic experimental strategy for conducting these studies. WIREs Dev Biol2017, 6:e280. doi: 10.1002/wdev.280 For further resources related to this article, please visit the WIREs website. Drosophila development progresses through four easily recognized life stages. Metabolism adapts to the energetic and biosynthetic demands of each developmental stage. Several methods are available for studying developmental metabolism in Drosophila.