Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2006
Publication Date: 11/29/2006
Citation: Kong, H.N., Patterson, C.D., Mitchell, R., Buyer, J.S., Aime, M.C., Lydon, J. 2006. A mutation in an exbd gene reduces tagetitoxin production by pseudomonas syringae pv tagetis. Canadian Journal of Microbiology. 52:1027-1035. Interpretive Summary: In order to reduce the risks to the environment, water, and food supply from the use of synthetic chemicals, more efficacious biological control agents for weeds are needed. The purpose of this study was to identify genes required for the production of a phytotoxin, tagetitoxin, produced by Pseudomonas syrinage pv. tagetis, a bacterial pathogen with biological activity on weeds in the Asteraceae family. To do so, we generated mutants of P. syrinage pv. tagetis, one of which did not produce tagetitoxin in infected plants and produced only small amounts of tagetitoxin in culture. We determined that the mutation in the toxin-production mutant is in a gene similar to exbD, a gene important in the transport of iron into Gram-negative cells. It was determined, however, that the mutation did not disrupt iron metabolism, or interfere in the production of iron scavenging compounds called siderophores. We conclude that the mutation in the gene involved in iron import probably had a direct or indirect effect on toxin export. The results of this study will be useful to scientists conduction research on the development and improvement of biological control agents of weeds.
Technical Abstract: In order to reduce the risks to the environment, water, and food supply from the use of synthetic chemicals, more efficacious biological control agents for weeds are needed. This purpose of this study was to identify genes required for the production of a phytotoxin, tagetitoxin, produced by a bacterial pathogen, Pseudomonas syringae pv. tagetis EBO37, that has potential a biological control agent of weeds in the Asteraceae family. A mutant of P. syringae pv. tagetis with limited ability to produce tagetitoxin was produced by transposon mutagenesis and the mutation characterized. We show that the transposon is inserted in a gene with homology to exbD. Contiguous with exbD are homologues of tonB and exbB (upstream) and a gene for a TonB-dependent receptor (downstream), indicating that mutation is in a gene cluster that expresses for a TonB membrane transport system. Reverse transcription analysis demonstrated that the mutation in exbD did not have a polar affect on a TonB-dependent receptor gene downstream from exbD. Tests were conducted to determine if the mutation in exbD affected iron metabolism. The exbD mutant was able to grow well in conditions where iron is not freely available. Siderophore production by the exbD mutant was similar to that of the wild-type strain. We conclude that the mutation in the exbD gene of P. syringae pv. tagetis disrupts tagetitoxin production without compromising iron metabolism. Furthermore, we believe that tagetitoxin export by P. syringae pv. tagetis involves an efflux pump that requires a functional TonB system that is not essential for normal iron metabolism. The results from this study will be of use to scientists conducting research on developing and improving biological agents of weeds.