Swarming regulation and bacteria-host interaction in Serratia marcescens:A novel lipoprotein SspA regulates S. marcescens swarming2,3-butanediol, a bacterial metabolite, ameliorates acute inflammatory response induced by LPS in rat model

Swarming in Serratia marcescens is a specialized form of bacterial surface migration. S. marcescens swarms at 30 ºC but not at 37 ºC on 0.8 % LB agar plate. To unravel the underlying mechanisms of the temperature-dependent swarming behavior, transposon mutagenesis was performed to screen for mutants that swarmed at 37 ºC. SspA, a novel lipoprotein, was identified to involve the negative regulation of S. marcescens swarming at 37 ºC. Increased production of biosurfactant, over-synthesis of flagellum and the reduced biofilm formation in sspA mutant S. marcescens SC101 all might contribute to the precocious-swarming behavior of S. marcescens SC101 at 37 ºC. Furthermore, the increased hemolytic activity of precocious-swarming mutant suggested that the regulation of swarming is closely related to the pathogenesis of S. marcescens. Besides, we also asked why S. marcescens is an important nosocomial pathogen. Herein, we showed that gastric intubation of 2,3-butanediol, a pyruvate metabolite produced by S. marcescens, in rats significantly ameliorates acute lung injury and the inflammatory responses induced by S. marcescens derived endotoxin lipopolysaccharide (LPS), with an efficacy comparable to that of the polyphenol compound resveratrol. Such effect was further demonstrated to occur via modulation of the NF-κB signaling pathway. Our results indicated that bacterial metabolite, 2,3-butanediol has a negative regulatory effect on host innate immunity response, suggesting bacteria may use some metabolites for host immune evasion.