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 (hereafter 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-acylhomoserine 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 flhDCflagellar 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.