Regulation of Transcription of Compatible Solute Transporters by the General Stress Sigma Factor, σ B , in Listeria monocytogenes

Abstract

ABSTRACT Listeria monocytogenes is well known for its durable physiological characteristics, which allow the organism to grow at low temperature and pH and high osmolarity. Growth under high osmolarity depends on the accumulation of compatible solutes, among which glycine betaine and carnitine are the preferred solutes for this organism. Three different transport systems, Gbu, BetL, and OpuC, have been identified in L. monocytogenes which serve to scavenge the preferred compatible solutes. The general stress response regulator σ B has been shown to play an important role in osmotic adaptation in L. monocytogenes , presumably by directing transcription from one or more of the solute transport genes. In the studies presented here, we have used primer extension analyses to identify the promoter elements responsible for transcription of the opuC , gbuA , and betL genes. All three genes are osmotically inducible to some degree. betL is transcribed from a σ B -independent promoter, while gbuA is transcribed from dual promoters, one of which is σ B dependent. opuC is transcribed exclusively from a σ B -dependent promoter. The betL promoter is similar in sequence to the σ B -independent gbuA P1 promoter. Kinetic analysis of transcript accumulation after osmotic upshift demonstrated that σ B -dependent transcripts from gbuA P2 and sigB accumulate for an extended period after upshift, suggesting that σ B activity may provide a mechanism for sustained high-level expression during osmotic challenge. In contrast to osmotic upshift, expression from the σ B -dependent opuC and gbuA P2 promoters after temperature upshift and ethanol stress was minimal, suggesting that additional mechanisms may also participate in regulating transcription from these σ B -dependent promoters.