JB Accepts, published online ahead of print on 23 October 2009

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J. Bacteriol. doi:10.1128/JB.00689-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Siderophore pyoverdine of Pseudomonas syringae pv. tabaci 6605 is intrinsic virulence factor in host tobacco infection

Fumiko Taguchi, Tomoko Suzuki, Yoshishige Inagaki, Kazuhiro Toyoda, Tomonori Shiraishi, and Yuki Ichinose^*

The Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka 1-1-1, Okayama 700-8530 Japan

^* To whom correspondence should be addressed. Email: yuki{at}cc.okayama-u.ac.jp.

To investigate the role of siderophore pyoverdine-mediated iron uptake in the virulence of the plant pathogen Pseudomonas syringae pv. tabaci 6605, three predicted pyoverdine synthesis-related genes, pvdJ, pvdL and fpvA, were mutated. The genes pvdJ, pvdL and fpvA encoded the pyoverdine side-chain peptide synthetase III L-Thr-L-Ser component, pyoverdine chromophore synthetase and TonB-dependent ferripyoverdine receptor, respectively. The pvdJ and pvdL mutants were unable to produce pyoverdine in MG medium as the iron-depleted condition. Furthermore, the pvdJ and pvdL mutants showed lower abilities to produce tabtoxin, extracellular polysaccharide and acyl homoserine lactones (AHLs), quorum-sensing molecules, and consequently had reduced virulence on host tobacco plants. In contrast, all of the mutants had accelerated swarming ability and increased biosurfactant production, suggesting that swarming motility and biosurfactant production might be negatively controlled by pyoverdine. Scanning electron micrographs of the surface of tobacco leaves inoculated with the mutant strains revealed only small amounts of extracellular polymeric matrix around these mutants, indicating disruption of mature biofilm. The tolerance to antibiotics was drastically increased in the pvdL mutant, similar to the psyI mutant, which is defective in AHLs production. These results demonstrated that pyoverdine synthesis and the quorum sensing system of Pseudomonas syringae pv. tabaci 6605 are indispensable for virulence in host tobacco infection, and that AHL may negatively regulate the tolerance to antibiotics.