RpoS regulates genes associated with development of the small cell variant developmental form of Coxiella burnetii

Coxiella burnetii, the etiological agent of Q fever, undergoes a unique biphasic developmental cycle where bacteria transition from replicating (exponential phase) large cell variant (LCV) forms to a non-replicating, (stationary phase) small cell variant (SCV) forms. The alternative sigma factor RpoS is an essential regulator of stress responses and stationary phase growth in several bacterial species, including Legionella pneumophila, which has a developmental cycle superficially similar to C. burnetii. To characterize RpoS function during C. burnetii growth and developmental, we constructed a C. burnetii ∆rpoS mutant to define the effects on intracellular and axenic growth, as well as, gene regulation during SCV development. C. burnetii ∆rpoS exhibited intracellular growth defects in J774 mouse macrophage-like cells, but not in Vero epithelial cells. RNA sequencing of C. burnetii ∆rpoS revealed that a substantial portion of the C. burnetii genome is regulated by RpoS during SCV development. Genes previously shown to have increased expression during SCV generation, including the expression of the SCV-specific protein ScvA and pathways involved in oxidative stress, arginine transport, and peptidoglycan remodeling pathways, were dysregulated in the rpoS mutant. These genes were enriched for a predicted RpoS-binding site. These data were corroborated with independent assays demonstrating that the C. burnetii rpoS mutant had increased sensitivity to hydrogen peroxide and carbenicillin. Collectively, these results demonstrate that RpoS is essential for the regulation of genes involved in SCV development and growth inside macrophage-like cells. Wild type vs. rpoS mutant At days 5 and 14, RNA was extracted using a hot trizol extraction