Identification and characterization of a putative ABC transporter PltHIJKN required for pyoluteorin production in Pseudomonas sp M 18

A putative ABC (ATP-binding cassette) transport gene cluster pltHIJKN was identified and characterized within a 7.5-kb genome region downstream of the antibiotic pyoluteorin (Plt) biosynthetic gene cluster in Pseudomonas sp. M18, a rhizosphere bacterium which is of ecological importance for controlling plant diseases caused by soil-borne fungal pathogens. The sequence similarity, conserved domains and hydrophobicity profiles strongly suggest that the pltHIJKN gene products are integrated into a typical three-component ABC export system, which consists of the inner membrane ABC transporter PltIJK, the membrane fusion protein PltH and the outer membrane efflux protein PltN. Mutant strains of M 18 defective in pltH or pltI did not produce detectable levels of Pit. Overexpression of the entire pltHIJKN gene cluster resulted in a significant increase of Pit production. Heterogenous expression of the pltHIJKN gene cluster gave rise to a significant enhancement of resistance of E. coli DH5 alpha to exogenous Plt. These results indicate that PltHIJKN is required for Pit biosynthesis and resistance, which is likely to be mediated by Pit export using the PltHIJKN transport system. Exogenous Pit induced the expression of both the Pit biosynthetic gene cluster and the ABC transport gene cluster pltHIJKN at the transcriptional level, suggesting that Plt biosynthesis and expression of pltHIJKN are coordinately and similarly regulated in Pseudomonas sp. M18. (c) 2006 Elsevier B.V. All rights reserved.