Biology subjects

Behrends, V.

Publications and source records attributed to Behrends, V..

6 recordsLinked to original sources

bioRxiv2025

The microbiota affects energy production, nitrogen excretion and sterol metabolism in mosquito larvae

Mosquito larvae rely on a living microbiota for normal development because the microbiota supplies essential nutrients, particularly vitamins. Beyond vitamin provision, transcriptomic data suggest that the microbiota also supports other key nutritional processes. Here, we explored these roles by conducting a metabolomics analysis on Aedes aegypti third instar larvae following microbiota depletion. We sampled larvae and dissected guts 12- and 20-hours post-decolonization and analysed methanol-soluble metabolites using untargeted gas chromatography-mass spectrometry. Our findings reveal a pronounced impact of gut microbial presence on several metabolites involved in the tricarboxylic acid cycle and the uricolytic pathway. Germ-free larvae also had a lower quantity of cholesterol in guts and their long-chain fatty acid profile was altered in guts and whole larvae. Sterols, including cholesterol, are essential precursors for the production of the moulting hormone 20-hydroxyecdysone. We therefore tested how supplementing exogenous cholesterol affects the development of germ-free larvae. The effects proved to be highly concentration-dependent, ranging from a marginally significant increase in successful development to adulthood at low concentrations to a pronounced developmental impairment at higher concentrations. Moreover, bacteria deficient in fatty acids beta-oxidation had a significantly lower ability to support larval development. Together, the observed alterations suggest that microbiota-deprived larvae exhibit a downregulation of metabolic processes related to energy production, nitrogen excretion and sterol metabolism, likely due to the absence of microbiota-derived vitamins essential for these central metabolic functions. ImportanceMosquito larvae depend on gut microbiota for normal growth because microbes supply essential nutrients, particularly B vitamins. To explore microbial roles beyond vitamin provision, we analysed metabolic changes in Aedes aegypti larvae after microbiota removal using gas chromatography-mass spectrometry. Germ-free larvae exhibited decreased metabolites associated with the tricarboxylic acid cycle and uricolytic pathway, indicating a general slowdown in metabolic activity and nitrogen waste processing. Additionally, the absence of a microbiota affected cholesterol and fatty acid metabolism. To validate these findings, we found that supplementing germ-free larvae with low levels of cholesterol modestly improved their development. In contrast, larvae colonized with bacteria deficient in fatty acid metabolism exhibited significantly reduced developmental success. Overall, the findings show that removing the microbiota downregulates key metabolic pathways related to energy production, nitrogen excretion, and sterol metabolism, highlighting that bacterial vitamins and fatty acid degradation are vital for mosquito larval development and successful transformation into adults.

microbiology↗

bioRxiv2025

Pleiotropic functions of glutathione in the adaptive response to long-term nitrogen starvation in Escherichia coli

Nitrogen (N) is essential for bacterial growth, and adaptation to N starvation involves extensive reprogramming of gene expression. A hallmark subcellular feature in long-term N starved Escherichia coli cells is the presence of biomolecular condensates of the major bacterial RNA regulator Hfq. The Hfq condensates, which accumulate gradually during N starvation, contribute to adaptation by modulating RNA metabolism and central metabolic pathways. Metabolites play central roles in stress responses, often acting as modulators of protein function to support survival and recovery. Glutathione (GSH), a universal stress protectant, has broad roles in bacterial stress adaptation, yet its function during N starvation remains unexplored. Using a GSH-deficient mutant ({Delta}gshAB), we show that GSH is required for optimal survival and recovery from prolonged N starvation. We reveal that GSH regulates the temporal dynamics of Hfq condensation and dissipation during starvation and recovery, respectively, via an as-yet unknown mechanism. Notably, these two functions of GSH appear mutually exclusive, highlighting its pleiotropic role in the adaptive response to N starvation that potentially extends its canonical function as a stress protectant. IMPORTANCENitrogen is a vital nutrient that bacteria need to grow. When nitrogen becomes scarce, bacteria must quickly adjust how their genes are used to survive. In Escherichia coli, one of the key changes during long-term nitrogen starvation is the formation of tiny structures inside the cell called Hfq condensates, which help manage genetic information flow and metabolism. Small molecules called metabolites play important roles in helping bacteria cope with stress, and one such molecule, glutathione (GSH), is known to protect cells under various stress conditions. However, its role during nitrogen starvation is not known. In this study, we used a mutant strain of E. coli that cannot produce GSH and found that these bacteria struggle to survive and recover from nitrogen starvation. We also discovered that GSH helps control when and how Hfq condensates form and disappear. Although, these two functions of GSH seem to be unrelated, our study highlights the versatile role of GSH in helping bacteria adapt to nitrogen stress.

microbiology↗

bioRxiv2025

Single-cell Analysis of Attenuation-Driven Transcription Reveals New Principles of Bacterial Gene Regulation

Transcription attenuation fine-tunes biosynthetic gene expression in bacteria via premature termination upon metabolic signals. In transcription initiation-controlled bacterial systems, promoter architecture and transcription factor binding sets the size of transcriptional bursts at {sigma}70 promoters, while distal enhancer elements and associated transcriptional activators modulate burst frequency at {sigma}54 promoters. Using the tryptophan biosynthesis operon as a model, we show that transcription attenuation, acting post-initiation and alongside transcriptional repression, simultaneously modulates both burst size and frequency from a {sigma}70 promoter. This challenges the view that frequency modulation requires distal enhancer input and reveals that post-initiation mechanisms can shape divergent transcriptional bursting. We also uncover that bacteria use cross-feeding as a previously unrecognised strategy for controlling cell-to-cell variation in gene expression, with implications for metabolic coordination among cells. These findings redefine transcription dynamics within cell populations and suggest new principles by which bacteria regulate gene expression to adapt to environmental change.

microbiology↗

bioRxiv2025

Condensation of the RNA chaperone Hfq is coupled to inhibition of carbon assimilation and contributes to the stabilisation of regulatory RNAs in nitrogen starved Escherichia coli

Ribonucleoprotein-condensates are membraneless compartments that concentrate RNA-binding proteins and RNA and play key roles in cellular adaptation across both eukaryotes and bacteria. While the biological roles of ribonucleoprotein-condensates are better understood in eukaryotic systems, the knowledge of metabolic processes that govern their formation and their contribution to stress adaptation remains at a nascent stage in bacterial RNA biology. Hfq is an RNA-chaperone conserved in many bacteria that undergoes condensation in response to diverse stresses. Using nitrogen (N) starvation in Escherichia coli as a model stress condition, we show that Hfq condensation occurs independently of any extracellular cues, cytoplasmic shrinkage that cells undergo during N starvation or the canonical NtrBC-dependent adaptive response to N starvation. However, we demonstrate that Hfq condensation is coupled to the inhibition of carbon assimilation in N-starved E. coli. Further, by comparing the transcriptomes of wild-type bacteria and bacteria unable to form Hfq-condensates, we reveal that Hfq-condensates contribute to the stabilisation of Hfq-associated non-coding regulatory RNAs. We propose that coordination of carbon and N metabolism during N starvation, critical for metabolic adaptation, is accompanied by preservation of non-coding regulatory RNAs via Hfq condensation.

microbiology↗

bioRxiv2020

Anopheles coluzzii stearoyl-CoA desaturase is essential for adult female survival and reproduction upon blood feeding

Vitellogenesis and oocyte maturation require anautogenous female Anopheles mosquitoes to obtain a bloodmeal from a vertebrate host. The bloodmeal is rich in proteins that are readily broken down into amino acids in the midgut lumen and absorbed by the midgut epithelial cells where they are converted into lipids and then transported to other tissues including ovaries. The stearoyl-CoA desaturase (SCD) plays a pivotal role in this process by converting saturated (SFAs) to unsaturated (UFAs) fatty acids; the latter being essential for maintaining cell membrane fluidity amongst other housekeeping functions. Here, we report the functional and phenotypic characterization of SCD1 in the malaria vector mosquito Anopheles coluzzii. We show that RNA interference (RNAi) silencing of SCD1 and administration of sterculic acid (SA), a small molecule inhibitor of SCD1, significantly impact on the survival and reproduction of female mosquitoes following blood feeding. Microscopic observations reveal that the mosquito thorax is quickly filled with blood, a phenomenon likely caused by the collapse of midgut epithelial cell membranes, and that epithelial cells are depleted of lipid droplets and oocytes fail to mature. Transcriptional profiling shows that genes involved in protein, lipid and carbohydrate metabolism and immunity-related genes are the most affected by SCD1 knock down (KD) in blood-fed mosquitoes. Metabolic profiling reveals that these mosquitoes exhibit increased amounts of saturated fatty acids and TCA cycle intermediates, highlighting the biochemical framework by which the SCD1 KD phenotype manifests as a result of a detrimental metabolic syndrome. Accumulation of SFAs is also the likely cause of the potent immune response observed in the absence of infection, which resembles an auto-inflammatory condition. These data provide insights into mosquito bloodmeal metabolism and lipid homeostasis and could inform efforts to develop novel interventions against mosquito-borne diseases.

microbiology↗

bioRxiv2017

GlnK facilitates the dynamic regulation of bacterial nitrogen assimilation

Ammonium assimilation in E. coli is regulated by two paralogous proteins (GlnB and GlnK), which orchestrate interactions with regulators of gene expression, transport proteins and metabolic pathways. Yet how they conjointly modulate the activity of glutamine synthetase (GS), the key enzyme for nitrogen assimilation, is poorly understood. We combine experiments and theory to study the dynamic roles of GlnB and GlnK during nitrogen starvation and upshift. We measure time-resolved in vivo concentrations of metabolites, total and post-translationally modified proteins, and develop a concise biochemical model of GlnB and GlnK that incorporates competition for active and allosteric sites, as well as functional sequestration of GlnK. The model predicts the responses of GS, GlnB and GlnK under time-varying external ammonium level in the wild type and two genetic knock-outs. Our results show that GlnK is tightly regulated under nitrogen-rich conditions, yet it is expressed during ammonium run-out and starvation. This suggests a role for GlnK as a buffer of nitrogen shock after starvation, and provides a further functional link between nitrogen and carbon metabolisms.

systems biology↗