Abstract
While the roles of rpoSBb and RpoS-dependent genes have been studied extensively within the mammal, the contribution of the RpoS regulon to the tick-phase of the Borrelia burgdorferi enzootic cycle has not been examined. Herein, we demonstrate that RpoS-dependent gene expression is prerequisite for the transmission of spirochetes by feeding nymphs. RpoS-deficient organisms are confined to the midgut lumen where they transform into an unusual morphotype (round bodies) during the later stages of the blood meal. We show that round body formation is rapidly reversible, and in vitro appears to be attributable, in part, to reduced levels of Coenzyme A disulfide reductase, which among other functions, provides NAD+ for glycolysis. Our data suggest that spirochetes default to an RpoS-independent program for round body formation upon sensing that the energetics for transmission are unfavorable.
Highlights
Bacterial genomes typically encode multiple alternative sigma factors that reversibly associate with the RNA polymerase apoenzyme to promote the transcription of specific subsets of genes in response to changing environmental conditions [1]
We began by devising an experimental strategy to test our hypothesis that one or more genes within the RpoS regulon are required for the dissemination of spirochetes during nymphal feeding
The time frames during which WT and DospC organisms were recovered from hemolymph cultures were highly similar in each experiment (n = 3; data not shown), suggesting that the cultured samples contained comparable numbers of organisms
Summary
Bacterial genomes typically encode multiple alternative sigma factors that reversibly associate with the RNA polymerase apoenzyme to promote the transcription of specific subsets of genes in response to changing environmental conditions [1]. One of the best studied alternative sigma factors is RpoS, the master regulator of the general stress response in E. coli (RpoSEc) [2,3]. Induction of the RpoSEc regulon occurs in response to a variety of stressors, including low nutrient availability, high osmolarity, reactive oxygen intermediates and low pH [4]. Up to 10% of the genome may be regulated either directly or indirectly by RpoSEc with the composition of the regulon determined by the specific stressor [5]. RpoS is essential for biofilm formation in Pseudomonas aeruginosa [7], growth and survival of Legionella pneumophila within phagolysosomes [8], and infectivity of mice by Salmonella enterica [9]
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