The ISME Journal - The host metabolite D-serine contributes to bacterial niche specificity through gene selection

Escherichia coli comprise a diverse array of both commensals and
niche-specific pathotypes. The ability to cause disease results from
both carriage of specific virulence factors and regulatory control of
these via environmental stimuli. Moreover, host metabolites
further refine the response of bacteria to their environment and can
dramatically affect the outcome of the host–pathogen interaction. Here,
we demonstrate that the host metabolite, D-serine, selectively affects
gene expression in E. coli O157:H7. Transcriptomic profiling
showed exposure to D-serine results in activation of the SOS response
and suppresses expression of the Type 3 Secretion System (T3SS) used to
attach to host cells. We also show that concurrent carriage of both the
D-serine tolerance locus (dsdCXA) and the locus of enterocyte
effacement pathogenicity island encoding a T3SS is extremely rare, a
genotype that we attribute to an ‘evolutionary incompatibility’ between
the two loci. This study demonstrates the importance of co-operation
between both core and pathogenic genetic elements in defining niche
specificity.