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Transcriptional profiling of Coxiella burnetii reveals extensive cell wall remodeling in the small cell variant developmental form

ABSTRACT: A hallmark of Coxiella burnetii, the bacterial cause of human Q fever, is a biphasic developmental cycle that generates biologically, ultrastructurally, and compositionally distinct large cell variant (LCV) and small cell variant (SCV) forms. LCVs are replicating, exponential phase forms while SCVs are non-replicating, stationary phase forms. The SCV has several properties, such as a condensed nucleoid and an unusual cell envelope, suspected of conferring enhanced environmental stability. To identify genetic determinants of the LCV to SCV transition, we profiled the C. burnetii transcriptome by microarray at 3 (early LCV), 5 (late LCV), 7 (intermediate forms), 14 (early SCV) and 21 days (late SCV) post-infection (PI) of Vero epithelial cells. Relative to early LCV, genes down-regulated in the SCV were primarily involved with intermediary metabolism. Up-regulated SCV genes included those involved in oxidative stress responses, arginine acquisition, and cell wall remodeling. A striking transcriptional signature of the SCV was induction (>7-fold) of five genes encoding predicted L,D transpeptidases that catalyze nonclassical 3-3 peptide cross-links in peptidoglycan (PG), a modification that can influence several biological traits in bacteria. Accordingly, of cross-links identified, muropeptide analysis showed PG of SCV with 46% 3-3 cross-links as opposed to 16% 3-3 cross-links for LCV. Moreover, cryo-electron microscopy revealed SCV with an unusually dense periplasmic layer that was intimately associated with the outer membrane. In contrast, LCV had a clearly distinguishable periplasm and inner/outer membranes. Collectively, these results indicate the SCV produces a unique transcriptome with a major component directed towards remodeling a PG layer that likely contributes to Coxiella's environmental resistance.

ORGANISM(S): Rickettsia rickettsii Staphylococcus epidermidis RP62A Staphylococcus epidermidis ATCC 12228 Coxiella burnetii RSA 493 Granulibacter bethesdensis Coxiella burnetii Chlamydia muridarum Chlamydia trachomatis D/UW-3/CX Staphylococcus haemolyticus JCSC1435 Borreliella burgdorferi B31 Chlamydia pneumoniae AR39 Staphylococcus aureus subsp. aureus MW2 Chlamydia caviae GPIC

PROVIDER: GSE74489 | GEO | 2016/02/10

SECONDARY ACCESSION(S): PRJNA300545

REPOSITORIES: GEO

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Project description:We have observed that for a number of S. aureus strains as they switch to a SCV lifestyle there is the formation of an extracellular matrix. We focused our analysis on one strain, WCH-SK2. For bacterial survival in the host, the combination of low nutrients and the prolonged timeframe forms a stress that selects for a specific cell-type from the population. In this context, we used steady-state growth conditions with low nutrients and a controlled low growth rate, for a prolonged time and with methylglyoxal. These conditions induced S. aureus WCH-SK2 into a stable SCV cell-type, they did not revert after sub-culturing. Methods: Transcriptomic profiles of wild-type (WT) and SCV were generated in continuous culture in the presence of stress (high and low level of methylglyoxal). Results: Analysis revealed these cells possessed a metabolic and surface profile that was different from previously described SCVs or biofilm cells. The extracellular matrix was protein and extracellular DNA; but not polysaccharide. The SCV cells induced expression of certain surface proteins (such as Ebh) and lantibiotic synthesis while down-regulating factors that stimulates immune response (leucocidin, capsule, carotenoid). We also studied further their genetic characteristics. They possessed an increased viability in the presence of antibiotics compared to their non-SCV form. Their stability implied there had been genetic changes, we determined the whole genome sequence of WCH-SK2 and its stable SCV forms at a single base resolution, employing Single Molecular Real-Time (SMRT) sequencing that also enables the methylome to be determined. The genetic features of this isolate have been identified; the SCCmec type, the pathogenicity and genetic islands and virulence factors. The comparison has identified a set of genetic changes that occurred in the stable SCV form; most notably to the global regulator MgrA and the phosphoserine phosphatase RsbU (part of the regulatory pathway of the sigma factor SigB). There was a shift in the methylation across the genome. Conclusions: Our data reveal a cell heterogeneity within a S. aureus population and using conditions that resemble long-term survival in the host has identified a previously unnoticed S. aureus cell-type, with a distinctive metabolic and molecular profile. The results from this study represent a unique identification of a suite of epigenetic, genetic and transcriptional factors that are implicated in the switch in S. aureus to its persistent SCV form

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Transcriptional profiling of Coxiella burnetii reveals extensive cell wall remodeling in the small cell variant developmental form

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