Biology and Control of Human Pathogens on Fresh Produce
Location: Produce Safety and Microbiology Research
Title: RcsB contributes to the distinct stress fitness between Escherichia coli O157:H7 curli variants of 1993 hamburger-associated outbreak strains
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2012
Publication Date: August 24, 2012
Citation: Carter, M.Q., Parker, C., Louie, J.W., Huynh, S., Fagerquist, C.K., Mandrell, R.E. 2012. RcsB contributes to the distinct stress fitness between Escherichia coli O157:H7 curli variants of 1993 hamburger-associated outbreak strains. Applied and Environmental Microbiology. doi:10.0028/AEM.02157-12.
Interpretive Summary: Curli is a bacterial appendage produced by many enteric bacteria and it enhances the initial attachment of bacteria to a solid surface and subsequently, the formation of biofilm. Curli is also an important virulence factor as they mediate host cell invasion, and are potent inducers of the host inflammatory response. E. coli O157:H7(EcO157)is the most common enterohemorrhagic E. coli serotype and contributes significantly to human infections and outbreaks in the US, and is a major public health concern. We reported previously that natural curli variants of EcO157 differ significantly in several phenotypes that are important for bacterial survival in both host and natural environments (AEM 77:3685-95). In this study, we details genetic basis of this fitness segregation in EcO157 population. We report that curli-producing variants of the 1993 hamburger-associated outbreak strains are natural rcsB mutants. Because RcsB protein functions as transcriptional regulator of several genes involved in different cellular processes, inactivation of RcsB in EcO157 C+ variants resulted in a marked decrease in cell resistance to acid stress and heat shock, but a large increase in nutrients uptake and catabolic activity in this subpopulation of EcO157 (curli producing variant). This study reveals a novel mechanism of altering curli production in enteric pathogens, and provides insight into the intra-population diversification in EcO157.
Curli are adhesive fimbriae of Enterobactericaeae and are involved in surface attachment, cell aggregation and biofilm formation. We previously reported that natural curli variants of E. coli O157:H7 (EcO157) displayed distinct acid resistance; however, this difference was not linked to the curli fimbriae per se. Here, we investigated the underlying molecular basis of this phenotypic divergence between the curli variants. We identified large deletions in the rcsB gene of curli-producing (C+) variants isolated from the 1993 U.S. hamburger-associated outbreaks strains. rcsB encodes the response regulator of RcsCDB two-component signal transduction system, which regulates curli biogenesis negatively, but acid resistance positively. Further comparison of stress fitness revealed that C+ variants were also significantly more sensitive to heat shock, but were resistant to osmotic stress and oxidative damage similar to curli-deficient (C-)variants. Transcriptomics analysis uncovered a large number of differentially expressed genes between the curli variants characterized by the enhanced expression in C+ variants of genes related to biofilm formation, virulence, catabolic activity and nutrients uptake, but marked decrease in transcription of genes related to various stress resistance. Supplying C+ variants with a functional rcsB restored cells resistance to heat shock and acid challenge, but blocked curli production, confirming that inactivation of RcsB in C+ variants was the basis of fitness segregation within the EcO157 population. This study provides an example of how genome instability of EcO157 promotes the intra-population diversification, generating sub-populations carrying an array of distinct phenotypes that may confer the pathogen survival advantages in host and non-host environments.