A core transcriptional response for biofilm formation by Y. pseudotuberculosis

Abstract

Previous transcriptional profiling of the enteropathogen Yersinia pseudotuberculosis during persis-tent stages of colonisation of mouse cecal lymphoid follicles indicated the possible involvement of biofilm in infection maintenance. Not much is known about the mechanisms responsible for biofilm formation by this pathogen, and most current knowledge is based on results of experiments con-ducted using the related Y. pestis pathogen that forms biofilm in the flea gut. In this study, we per-formed transcriptional profiling of Y. pseudotuberculosis in biofilms from different biofilm-inducing conditions, bile exposure, amino acid deprivation and in vivo mimicking conditions with and with-out oxygen. The comparison of differential expression of genes in biofilm versus planktonic bacteria showed a set of 54 core genes that were similarly regulated, independent of inducing condition. This set included many genes that were previously shown to be associated with biofilms, such as hutG, hsmF, hmsT and cpxP that were upregulated and other genes such as hmsP and rfaH that were downregulated. There were also novel biofilm-associated genes, including genes encoding hypo-thetical proteins. To identify the genes involved in inducing biofilm formation, the gene expression of bacteria during an early initial phase when biofilm starts to form after induction by bile or amino acid depletion was determined. Comparisons of the resulting gene expression profiles with the pro-files of non-induced bacteria incubated for the same period of time showed a set of core genes asso-ciated with early biofilm formation. This set included genes involved in quorum sensing, pili bio-genesis and genes indicative of a potential metabolic shift involving nitrogen utilisation. Genes en-coding components of sugar phosphotransferase systems were also upregulated during biofilm in-duction. Assays of biofilm formation by bacteria deleted of some of these core genes showed that strains lacking hpr and luxS, which are known to be important for functional sugar phosphotransfer-ase systems and quorum sensing, as well as glnL encoding a sensory histidine kinase were most negatively affected. Most of the deletion mutant strains tested were affected, but the effect was less severe, suggesting high levels of redundancy in the pathways involved in biofilm formation by this pathogen.