|Han, Song Hee|
|Kim, Chul Hong|
|Lee, Jang Hoon|
|Park, Ju Yeon|
|Cho, Song Mi|
|Park, Seur Kee|
|Kim, Kil Yong|
|Kim, Young Cheol|
Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2008
Publication Date: 3/18/2008
Citation: Han, S., Kim, C., Lee, J., Park, J., Cho, S., Park, S., Kim, K., Krishnan, H.B., Kim, Y. 2008. Inactivation of pqq Genes of Enterobacter Intermedium 60-2G Reduces Antifungal Activity and Induction of Systemic Resistance. FEMS Microbiology Letters. 282:140-146. Interpretive Summary: Phosphorus, an essential mineral macronutrient, is required for maximum yield of agriculturally important crops. Soil contains only a small percentage of the total phosphorus in a soluble form. The rest is chemically bound in insoluble complexes (mineral phosphate). Farmers are thus asked to apply several-fold excess phosphorus fertilizers in order to overcome this problem. Certain strains of Rhizobium, Pseudomonas, and Bacillus species have the ability to solubilize mineral phosphate into forms that can be utilized by the plants for their growth and development. Enterobacter intermedium 60-2G, a soil bacterium has a strong ability to solubilize phosphate and promote plant growth and suppress plant disease due to induction of systemic resistance. In this basic study, we have demonstrated that the ppqA and ppqB genes are required for phosphate solubilization and induced systemic resistance against a soft rot pathogen. Information obtained from this basic study demonstrates that Enterobacter intermedium 60-2G can be utilized as a potential biofertilizer to promote maximum yield and reduce the use of expensive phosphorus fertilizers.
Technical Abstract: Enterobacter intermedium 60-2G, a phosphate solubilizing bacterium, has the ability to induce systemic resistance in plants against soft rot pathogen Erwinia carotovora. Phosphate solubilization is mediated by the production of organic acids. Glucose dehydrogenase, an enzyme which utilizes pyrroloquinoline quinone (PQQ) as a cofactor, is required for the synthesis of gluconic acid by E. intermedium 60-2G. PQQ is produced via the activity of enzymes encoded by the pqqABCDEF operon. Here, we report that the ppqA and ppqB genes are required for phosphate solubilization and induced systemic resistance in tobacco against a soft rot pathogen. Mutations in either the pqqA or pqqB gene abolished the production of 2-ketogluconic acid and eliminated the ability of E. intermedium to solubilize hydroxyapatite. Addition of gluconic acid to the growth media restored the ability of the ppqA mutant to produce 2-ketogluconic acid. Interestingly, both pqqA and pqqB mutants of E. intermedium lost their ability to inhibit the growth of the rice pathogen Magnaporthe grisea KI-409. Additionally, induced systemic resistance against the soft rot pathogen was attenuated in the pqq mutants. These functions were restored by complementation with the wild type pqq gene cluster. Our findings suggest that PQQ plays an important function in the beneficial traits including phosphate solubilization, antifungal activity, and induced systemic resistance of E. intermedium, possibly by acting as a cofactor for several enzymes including glucose dehydrogenase.