Biology subjects

Winter, M. G.

Publications and source records attributed to Winter, M. G..

3 recordsLinked to original sources

bioRxiv2024

Gene regulation of infection-associated L-tartrate metabolism in Salmonella enterica serovar Typhimurium

Enteric pathogens such as Salmonella enterica serovar Typhimurium experience spatial and temporal changes to the metabolic landscape throughout infection. Host reactive oxygen and nitrogen species non-enzymatically convert monosaccharides to alpha hydroxy acids, including L-tartrate. Salmonella utilizes L-tartrate early during infection to support fumarate respiration, while L-tartrate utilization ceases at later time points due to the increased availability of exogenous electron acceptors such as tetrathionate, nitrate, and oxygen. It remains unknown how Salmonella regulates its gene expression to metabolically adapt to changing nutritional environments. Here, we investigated how the transcriptional regulation for L-tartrate metabolism in Salmonella is influenced by infection-relevant cues. L-tartrate induces the transcription of ttdBAU, genes involved in L-tartrate utilization. L-tartrate metabolism is negatively regulated by two previously uncharacterized transcriptional regulators TtdV (STM3357) and TtdW (STM3358), and both TtdV and TtdW are required for sensing of L-tartrate. The electron acceptors nitrate, tetrathionate, and oxygen repress ttdBAU transcription via the two-component system ArcAB. Furthermore, regulation of L-tartrate metabolism is required for optimal fitness in a mouse model of Salmonella-induced colitis. TtdV, TtdW, and ArcAB allow for the integration of two cues, substrate availability and availability of exogenous electron acceptors, to control L-tartrate metabolism. Our findings provide novel insights into how Salmonella prioritizes utilization of different electron acceptors for respiration as it experiences transitional nutrient availability throughout infection. IMPORTANCEBacterial pathogens must adapt their gene expression profiles to cope with diverse environments encountered during infection. This coordinated process is carried out by the integration of cues that the pathogen senses to fine-tune gene expression in a spatiotemporal manner. Many studies have elucidated the regulatory mechanisms on how Salmonella sense metabolites in the gut to activate or repress its virulence program, however our understanding of how Salmonella coordinates its gene expression to maximize the utilization of carbon and energy sources found in transitional nutrient niches is not well understood. In this study, we discovered how Salmonella integrates two infection-relevant cues, substrate availability and exogenous electron acceptors, to control L-tartrate metabolism. From our experiments, we propose a model for how L-tartrate metabolism is regulated in response to different metabolic cues in addition to characterizing two previously unknown transcriptional regulators. This study expands our understanding of how microbes combine metabolic cues to enhance fitness during infection.

microbiology↗

bioRxiv2023

Byproducts of inflammatory radical metabolism provide transient nutrient niches for microbes in the inflamed gut

Louis Pasteurs experiments on tartaric acid laid the foundation for our understanding of molecular chirality, but major questions remain. By comparing the optical activity of naturally-occurring tartaric acid with chemically-synthesized paratartaric acid, Pasteur realized that naturally-occurring tartaric acid contained only L-tartaric acid while paratartaric acid consisted of a racemic mixture of D- and L-tartaric acid. Curiously, D-tartaric acid has no known natural source, yet several gut bacteria specifically degrade D-tartaric acid. Here, we investigated the oxidation of monosaccharides by inflammatory reactive oxygen and nitrogen species. We found that this reaction yields an array of alpha hydroxy carboxylic acids, including tartaric acid isomers. Utilization of inflammation- derived D- and L-tartaric acid enhanced colonization by Salmonella Typhimurium and E. coli in murine models of gut inflammation. Our findings suggest that byproducts of inflammatory radical metabolism, such as tartrate and other alpha hydroxy carboxylic acids, create transient nutrient niches for enteric pathogens and other potentially harmful bacteria. Furthermore, this work illustrates that inflammatory radicals generate a zoo of molecules, some of which may erroneously presumed to be xenobiotics.

microbiology↗

bioRxiv2022

Taxonomic and metagenomic analyses define the development of the microbiota in the chick

Chicks are ideal to follow the development of the intestinal microbiota and to understand how a pathogen perturbs this developing population. Taxonomic/metagenomic analyses captured the development of the chick microbiota in unperturbed chicks and in chicks infected with Salmonella enterica serotype Typhimurium (STm) during development. Taxonomic analysis suggests that colonization by the chicken microbiota takes place in several waves. The cecal microbiota stabilizes at day 12 post-hatch with prominent Gammaproteobacteria and Clostridiales. Introduction of S. Typhimurium at day 4 post-hatch disrupted the expected waves of intestinal colonization. Taxonomic and metagenomic shotgun sequencing analyses allowed us to identify species present in uninfected chicks. Untargeted metabolomics suggested different metabolic activities in infected chick microbiota. This analysis, and GS-MS on ingesta confirmed that lactic acid in cecal content coincides with the stable presence of Enterococci in STm infected chicks. Unique metabolites including 2-isopropylmalic acid, an intermediate in the biosynthesis of leucine, was present only in the cecal content of STm infected chicks. Metagenomic data suggested that the microbiota in STm infected chicks contained a higher abundance of genes, from STm itself, involved in branched chain amino acid synthesis. We generated a deletion mutant in ilvC (STM3909) encoding ketol-acid-reductoisomerase, a gene required for the production of L-isoleucine and L-valine. {Delta}ilvC mutants are disadvantaged for growth during competitive infection with the wild type. Providing the ilvC gene in trans restored growth of the {Delta}ilvC mutant. Our integrative approach identified biochemical pathways used by STm to establish a colonization niche in the chick intestine during development. IMPORTANCEChicks are an ideal model to follow the development of the intestinal microbiota and to understand how a pathogen perturbs this developing population. Using taxonomic and metagenomic analyses we captured the development of the chick microbiota to 19 days post-hatch in unperturbed chicks and in chicks infected with Salmonella enterica serotype Typhimurium (STm). We show that normal development of the microbiota takes place in waves, and is altered in the presence of a pathogen. Metagenomics and metabolomics suggested that branched chain amino acid biosynthesis is especially important for Salmonella growth in the infected chick intestine. Salmonella mutants unable to make L-isoleucine and L-valine colonize the chick intestine poorly. Restoration of the pathway for biosynthesis of these amino acids restored the colonizing ability of Salmonella. Integration of multiple analyses allowed us to correctly identify biochemical pathways used by Salmonella to establish a niche for colonization in the chick intestine during development.

microbiology↗