Heterologous acyl-homoserine lactone synthase expression in Pseudomonas putida

Many bacteria harbor an incomplete quorum sensing system, wherein they possess LuxR homologues without the quorum sensing acyl-homoserine lactone (AHL) synthase, which is encoded by a luxI homolog. An artificial AHL-producing plasmid was constructed using a cviI gene encoding for C6-AHL (HHL) synthase from Chromobacterium violaceum and was introduced successfully into both wild-type and the ppoR (a luxR homolog) mutant. Our data provides evidence to suggest that the PpoR-HHL complex, but neither PpoR nor HHL alone, could attenuate growth, antibiotic resistance, and biofilm formation ability. In contrast, swimming motility, siderophore production, and indole degradation were enhanced by PpoR-HHL. The addition of exogenous indole increased biofilm formation and reduce swimming motility. Interestingly, indole proved ineffective in the presence of PpoR-HHL, thereby suggesting that the PpoR-HHL complex masks the effects of indole. Our data was supported by transcriptome analyses showing that the presence of the plasmid-encoded AHL synthase altered the expression of many genes on the chromosome in strain KT2440. Our results showed that heterologous luxI expression occurring via horizontal gene transfer can regulate a broad range of specific target genes, resulting in alterations of the phenotype and physiology of host cells. Strains: wild-type (pRK415), wild-type (pHHL), luxR mutant (pRK415), luxR mutant (pHHL) Medium: M9 minimal medium supplemented with 10 mM glucose and 10 mM succinate Temperature: 28 °C