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Published online ahead of print on 15 October 2009 as doi:10.1099/mic.0.031161-0
Microbiology (2009), DOI 10.1099/mic.0.031161-0
© 2009 Society for General Microbiology
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Microbiology 0 (2009), mic.0.031161; DOI  10.1099/mic.0.031161-0
© 2009 Society for General Microbiology

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

Tao Tian1, Xiao-Gang Wu1, Hui-Mei Duan1 and Li-Qun Zhang2,3

1 Department of Plant Pathology, China Agricultural University;
2 China Agricultural University

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 production of 2,4-DAPG were isolated using transposon mutagenesis. The disrupted genes in these 2 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 accumulation of 2,4-DAPG, whereas the deletion of 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 the EmhABC pump on the transcription of the 2,4-DAPG biosynthetic locus. 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 suggested that the EmhABC system is an important element influencing the production of antibiotic 2,4-DAPG and for enhancing resistance to toxic compounds in P. fluorescens 2P24.

3 E-mail: zhanglq{at}cau.edu.cn






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