Isolation and functional analysis of luxS in Serratia plymuthica RVH1

Autoinducer-2 (AI-2) is a signalling molecule proposed to act as a 'universal' signal for interspecies communication, regulating niche-specific genes with diverse functions in various bacteria. We have previously reported the production of AI-2 in strains from different Serratia species and recently, the luxS gene of two Serratia strains was isolated and shown to affect distinct phenotypes. In the current work, we have identified the luxS gene of Serratia plymuthica RVH1, and studied its effect on the N-acyl-L-homoserine lactone-regulated 2,3-butanediol fermentation, production of extracellular protease, chitinase, nuclease and antibacterial compound, and on biofilm formation. None of these phenotypes was affected by luxS knockout. However, overexpression of the luxS gene in RVH1, which was accompanied by an increased production of AI-2, resulted in a slower growth. This growth retardation was also observed when RVH1 was grown in spent culture medium from the AI-2-overproducing strain, but not in spent culture medium from the luxS knockout strain. These results suggest that luxS primarily fulfils a metabolic role and may not regulate a coordinated behaviour controlled by cell-to-cell signalling in S. plymuthica RVH1.