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Title: Involvement of phenazines and biosurfactants in biocontrol of Pythium myriotylum root rot on cocoyam by Pseudomonas sp. CMR12A

item D'AES, J. - Ghent University
item DE MAEYER, K. - Ghent University
item LEYS, T - Ghent University
item MAVRODI, D. - Washington State University
item Thomashow, Linda
item HOFTE, M. - Ghent University

Submitted to: International Plant Growth Promoting Rhizobacteria Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 2/16/2009
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Pseudomonas sp. CMR12a was isolated from the rhizosphere of the tropical tuber crop cocoyam and produces both phenazines and cyclic lipopeptide (CLP) biosurfactants. CMR12a was shown to be an efficient biocontrol agent of P. myriotylum on cocoyam. To assess the importance of phenazine and biosurfactant production for its antagonism, biosynthesis mutants were constructed in CMR12a by site specific mutagenesis. The phenazine mutant, CMR12a-'phz, no longer produced phenazines, whereas other characteristics were comparable to that of the wild type. The most outstanding features of CMR12a-CLP, the biosurfactant mutant, were deficiency for CLP production, an altered swarming morphology and, remarkably, an increased production of phenazines. In vitro, spent culture supernatant of CMR12a and CMR12a-'phz strongly inhibited growth of P. myriotylum, whereas the supernatant of CMR12a-CLP could not visibly reduce the growth of the pathogen. Infection experiments showed that CMR12a-'phz still provided biocontrol towards P. myriotylum, while CMR12a-CLP lost most of its biocontrol capacity, although it was still able to colonize the cocoyam roots. These observations indicate that the ability of CMR12a to suppress P. myriotylum on cocoyam can mainly be attributed to its biosurfactant production. Consequently, the biocontrol mechanism appears to be different from that of P. aeruginosa PNA1, for which it was shown that phenazines and biosurfactants act synergistically in the biocontrol of P. myriotylum on cocoyam.