title: Characterization of a stress-induced alternate sigma factor, RpoS, of Coxiella burnetii and its expression during the development cycle.
abstract: Coxiella burnetii is an obligate intracellular bacterium that resides in an acidified phagolysosome and has a remarkable ability to persist in the extracellular environment. C. burnetii has evolved a developmental cycle that includes at least two morphologic forms, designated large cell variants (LCV) and small cell variants (SCV). Based on differential protein expression, distinct ultrastructures, and different metabolic activities, we speculated that LCV and SCV are similar to typical logarithmic- and stationary-phase growth stages. We hypothesized that the alternate sigma factor, RpoS, a global regulator of genes expressed under stationary-phase, starvation, and stress conditions in many bacteria, regulates differential expression in life cycle variants of C. burnetii. To test this hypothesis, we cloned and characterized the major sigma factor, encoded by an rpoD homologue, and the stress response sigma factor, encoded by an rpoS homologue. The rpoS gene was cloned by complementation of an Escherichia coli rpoS null mutant containing an RpoS-dependent lacZ fusion (osmY::lacZ). Expression of C. burnetii rpoS was regulated by growth phase in E. coli (induced upon entry into stationary phase). A glutathione S-transferase-RpoS fusion protein was used to develop polyclonal antiserum against C. burnetii RpoS. Western blot analysis detected abundant RpoS in LCV but not in SCV. These results suggest that LCV and SCV are not comparable to logarithmic and stationary phases of growth and may represent a novel adaptation for survival in both the phagolysosome and the extracellular environment.
authors.affiliation: Department of Medical Microbiology and Immunology, Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA.
authors.forename: R
authors.initials: R
authors.lastname: Seshadri
authors.forename: J E
authors.initials: JE
authors.lastname: Samuel
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002374:Catalase / Q000378:metabolism; D003001:Cloning, Molecular; D016997:Coxiella burnetii / Q000235:genetics* / Q000254:growth & development; D004269:DNA, Bacterial; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D004926:Escherichia coli; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D011817:Rabbits; D017422:Sequence Analysis, DNA; D012808:Sigma Factor / Q000235:genetics*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D002374:Catalase; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; D001616:beta-Galactosidase