title: The role of the transcriptional regulator, DsdC, in Escherichia coli pathogenicity
Creators: name: Turner, Natasha C.A.
Publisher: name: University of Glasgow
Year: 2021

description: Within the mammalian host, bacteria are exposed to a large number of nutritional and chemical stimuli. Modification of gene transcription, in response to environmental signals, enables bacteria to compete and adapt within their preferred niches. D-serine is a host metabolite that has become a focus in recent years due to its diverse roles in neurotransmission and signalling in humans, as well as its unique role in affecting gene expression in bacteria. Indeed, previous work from the Roe laboratory revealed that D-serine played a critical role in controlling the expression of a main virulence determinant in enterohaemorrhagic Escherichia coli (EHEC), the type three secretion system (T3SS). Conversely, some commensal and extraintestinal pathogenic E. coli (ExPEC) can catabolise D-serine, using it as a carbon source. Uropathogenic E. coli (UPEC) and neonatal meningitis-associated E. coli (NMEC) represent two clinically relevant pathotypes of ExPEC, that are causal agents of a spectrum of diseases in mammals from uncomplicated urinary tract infections (UTIs), to bacteraemia, and meningitis. ExPEC are distinct amongst E. coli in their ability to colonise several anatomical niches within the host. ExPEC strains are able to survive outside of the intestine, partly due to their ability to catabolise a diverse range of host metabolites, including D-serine. UPEC and NMEC carry a locus, dsdCXA, for D-serine metabolism. DsdC, a LysR-type transcriptional regulator (LTTR), autoregulates its own expression and further controls the expression of DsdX, a D-serine inner membrane transporter and DsdA, a D-serine deaminase that catabolises D-serine into pyruvate and ammonia. Strikingly, NMEC strains carry two copies of the dsdCXA locus: dsdCXA1 and dsdCXA2. Metabolism and virulence are often interlinked in bacteria, with host metabolites, in addition to being carbon sources, acting as environmental signals that can affect bacterial gene expression. It was thus hypothesised that Dserine, which is abundant in the brain and urinary tract, may act as an environmental stimulus that enables two ExPEC pathogens to sense their environment and modify their gene expression, through the regulatory actions of DsdC. In this work, using a combination of chromatin immunoprecipitation coupled with next generation sequencing (ChIP-Seq) and RNA sequencing (RNA-Seq), the direct regulon of DsdC in two prototypical UPEC and NMEC strains, CFT073 and CE10, was elucidated, in the presence and absence of D-serine. It was shown that DsdC bound to distinct regions of both the CFT073 and CE10 genome, indicating that DsdC has been tailored for strain-specific lifestyles. In CFT073, it was shown that DsdC bound and affected expression of genes involved in colibactin synthesis, a bacterial genotoxin. Furthermore, it was revealed that in CE10, DsdC bound and affected expression of several genes involved in outer membrane-associated virulence, such as capsular and LPS biosynthesis genes. Using a range of biochemical techniques, it was established that DsdC, upon exposure to D-serine, modified the O-antigen structure of CE10. Furthermore, it was revealed that DsdC1, but not DsdC2, affected the survival of CE10 against K1-specific bacteriophages, through the regulation of the O-acetyltransferase gene neuO, elucidating a distinct role for the homologous proteins. Collectively, this work describes how regulation by DsdC has been tailored to suit strainspecific lifestyles in two ExPEC strains and further enhances our understanding of how bacterial pathogens sense their environment and mediate pathogenesis.