The role of RsmA in the regulation of swarming motility in Serratia marcescens

Swarming motility is a multicellular phenomenon comprising population migration across surfaces by specially differentiated cells. In Serratia marcescens, a network exists in which the flhDC flagellar regulatory master operon, temperature, nutrient status, and quorum sensing all contribute to the regulation of swarming motility, In this study, the rsmA (repressor of secondary metabolites) gene thereafter rsmA(Sm)) was cloned from S. marcescens. The presence of multicopy, plasmid-encoded rsmA(Sm) expressed from its native promoter in S, marcescens inhibits swarming. Synthesis of N-acyl homoserine lactones, presumably by the product of smal (a luxl homolog isolated from S, marcescens), was also inhibited. Knockout of rsmA(Sm) on the S. marcescens chromosome shortens the time before swarming motility begins after inoculation to an agar surface. A single copy of the chromosomal PrsmA(Sm)::luxAB reporter of rsmA(Sm), transcription was constructed. Using this reporter, the roles of the flhDC flagellar regulatory master operon, temperature and autoregulation in the control of rsmA(Sm) expression were determined. Our findings indicate that RsmA(Sm) is a component of the complex regulatory network that controls swarming, Copyright (C) 2001 National Science Council, ROC and S. Karger AG, Basel.