The resistance-nodulation-division efflux pump EmhABC influences the production of 2,4-diacetylphloroglucinol in Pseudomonas fluorescens 2P24

1 Department of Plant Pathology, China Agricultural University, Beijing, 100193, PR China 2 The Key Laboratory of Plant Pathology, Ministry of Agriculture, Beijing, 100193, PR China The polyketide metabolite 2,4-diacetylphloroglucinol (2,4-DAPG) plays a major role in the biological control of soil-borne plant diseases by Pseudomonas fluorescens 2P24. Two mutants (PM810 and PM820) with increased extracellular accumulation of 2,4-DAPG were isolated using transposon mutagenesis. The disrupted genes in these two mutants shared >80 % identity with the genes of the EmhR–EmhABC resistance-nodulation-division (RND) efflux system of P. fluorescens cLP6a. The deletion of emhA (PM802), emhB (PM803) or emhC (PM804) genes in strain 2P24 increased the extracellular accumulation of 2,4-DAPG, whereas the deletion of the emhR (PM801) gene decreased the biosynthesis of 2,4-DAPG. The promoter assay confirmed the elevated transcription of emhABC in the EmhR disrupted strain (PM801) and an indirect negative regulation of 2,4-DAPG biosynthetic locus transcription by the EmhABC efflux pump. Induction by exogenous 2,4-DAPG led to remarkable differences in transcription of chromosome-borne phlA : : lacZ fusion in PM901 and PM811 ( emhA – ) strains. Additionally, the EmhABC system in strain 2P24 was involved in the resistance to a group of toxic compounds, including ampicillin, chloramphenicol, tetracycline, ethidium bromide and crystal violet. In conclusion, our results suggest that the EmhABC system is an important element that influences the production of antibiotic 2,4-DAPG and enhances resistance to toxic compounds in P. fluorescens 2P24. Correspondence Li-Qun Zhang zhanglq{at}cau.edu.cn Abbreviations: 2,4-DAPG, 2,4-diacetylphloroglucinol; EB, ethidium bromide; KB, King's B; LB, Luria–Bertani broth; RND, resistance nodulation division; T3SS, type III secretion system The GenBank/EMBL/DDBJ accession number for the DNA sequence containing the emhR–emhABC genes of P. fluorescens 2P24 is FJ807391. Four supplementary figures and a supplementary table are available with the online version of this paper.