Differential regulation of three DMSO reductases during enteric salmonellosis

PROJECT SUMMARY Non-typhoidal Salmonella are successful foodborne pathogens in part because of their ability to utilize diverse nutrient sources to support disease in many hosts. Within the mammalian gut, catabolism of organosulfur compounds by the host and/or the microbiota can lead to production of the electron acceptor dimethyl sulfoxide (DMSO). The genome of Escherichia coli K12, a closely related gut-commensal bacterium, encodes a single co- transcribed operon dedicated to the anaerobic reduction of DMSO (dmsABC) and has been used as a model system to study DMSO respiration in Enterobacteriaceae. In contrast, Salmonella serotypes that cause enteric disease encode three operons homologous to dmsABC, suggesting this pathway is important to support fitness within the gut. Our prior work demonstrates that DMSO reduction is a biologically relevant pathway to support Salmonella fitness during acute intestinal colonization. In vitro phenotyping suggests STM0964 is the dominant homolog of dmsA, the catalytic subunit of a DMSO reductase, while STM4305 acts an alternate dmsA homolog during anaerobic growth. However, there is a critical gap in our understanding of how the bacterium regulates the use of each DMSO reductase and how each DMSO reductase contributes to fitness during enteric infection. Genetic redundancy in anaerobic respiration pathways is a common theme in Enterobacteriaceae that allows bacteria to benefit from changes in nutrient availability to regulate fitness in the gut. My preliminary data shows that DMSO increases the promoter activity of the alternate dmsA homolog, STM4305. The promoter activity of the dominant dmsA homolog, STM0964, is not activated by DMSO akin to E. coli dmsA, suggesting that Salmonella possesses a novel mechanism for transcriptional regulation by DMSO. I hypothesize that differential activation of DMSO reductases supports Salmonella fitness within the gut. In Aim I, I will establish a mechanism for DMSO-mediated transcriptional regulation of the alternate DMSO reductase using biochemical, genetic and RNA sequencing approaches. In Aim II, I will utilize fluorescence microscopy and competitive infections to elucidate the contribution of each DMSO reductase during enteric infection of the bovine host. The proposed work will integrate my veterinary training with large animal modeling of enteric disease and advanced gene expression analysis to establish how Salmonella benefits from apparent genetic redundancy in DMSO reduction. At the completion of fellowship training, I will be poised for success in a career as an independent clinician-scientist with expertise in genetic approaches and animal modeling to study infectious diseases of One Health significance.