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Infection and Immunity, August 2001, p. 4874-4883, Vol. 69, No. 8
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.8.4874-4883.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Characterization of a Stress-Induced Alternate Sigma Factor, RpoS, of Coxiella burnetii and Its Expression during the Development Cycle

Rekha Seshadri and James E. Samuel*

Department of Medical Microbiology and Immunology, Texas A&M University System Health Science Center, College Station, Texas 77843-1114

Received 1 February 2001/Returned for modification 21 March 2001/Accepted 16 May 2001

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.

* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, 407 Reynolds Medical Building, Texas A&M University System Health Sciences Center, College Station, TX 77843-1114. Phone: (979) 862-1684. Fax: (979) 845-3479. E-mail: jsamuel{at}tamu.edu.

Infection and Immunity, August 2001, p. 4874-4883, Vol. 69, No. 8
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.8.4874-4883.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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