Interplay between orfamides, sessilins and phenazines in the control of Rhizoctonia diseases by Pseudomonas sp. CMR12a.

We investigated the role of phenazines and cyclic lipopeptides (CLPs) (orfamides and sessilins), antagonistic metabolites produced by Pseudomonas sp. CMR12a, in the biological control of damping-off disease on Chinese cabbage (Brassica chinensis) caused by Rhizoctonia solani AG 2-1 and root rot disease on bean (Phaseolus vulgaris L.) caused by R. solani AG 4-HGI. A Pseudomonas mutant that only produced phenazines suppressed damping-off disease on Chinese cabbage to the same extent as CMR12a, while its efficacy to reduce root rot on bean was strongly impaired. In both pathosystems, the phenazine mutant that produced both CLPs was equally effective, but mutants that produced only one CLP lost biocontrol activity. In vitro microscopic assays revealed that mutants that only produced sessilins or orfamides inhibited mycelial growth of R. solani when applied together, while they were ineffective on their own. Phenazine-1-carboxamide suppressed mycelial growth of R. solani AG 2-1 but had no effect on AG 4-HGI. Orfamide B suppressed mycelial growth of both R. solani anastomosis groups in a dose-dependent way. Our results point to an additive interaction between both CLPs. Moreover, phenazines alone are sufficient to suppress Rhizoctonia disease on Chinese cabbage, while they need to work in tandem with the CLPs on bean.

Olorunleke FE ，Hua GK ，Kieu NP ，Ma Z ，Höfte M ... -  《Environmental Microbiology Reports》

Biological control of Rhizoctonia root rot on bean by phenazine- and cyclic lipopeptide-producing Pseudomonas CMR12a.

D'aes J ，Hua GK ，De Maeyer K ，Pannecoucque J ，Forrez I ，Ongena M ，Dietrich LE ，Thomashow LS ，Mavrodi DV ，Höfte M ... -  《PHYTOPATHOLOGY》

Role of phenazines and cyclic lipopeptides produced by pseudomonas sp. CMR12a in induced systemic resistance on rice and bean.

Pseudomonas sp. CMR12a produces two different classes of cyclic lipopeptides (CLPs) (orfamides and sessilins), which all play a role in direct antagonism against soilborne pathogens. Here we show that Pseudomonas sp. CMR12a is also able to induce systemic resistance to Magnaporthe oryzae on rice and to the web blight pathogen Rhizoctonia solani AG2-2 on bean. Plant assays with biosynthesis mutants of Pseudomonas sp. CMR12a impaired in the production of phenazines and/or CLPs and purified metabolites revealed that distinct bacterial determinants are responsible for inducing systemic resistance in these two pathosystems. In rice, mutants impaired in phenazine production completely lost their ability to induce systemic resistance, while a soil drench with pure phenazine-1-carboxamide (PCN) at a concentration of 0.1 or 1 μM was active in inducing resistance against M. oryzae. In bean, mutants that only produced phenazines, sessilins or orfamides were still able to induce systemic resistance against Rhizoctonia web blight, but a balanced production of these metabolites was needed. This study not only shows that Pseudomonas sp. CMR12a can protect rice to blast disease and bean to web blight disease, but also displays that the determinants involved in induced systemic resistance are plant, pathogen and concentration dependent.

Ma Z ，Hua GKH ，Ongena M ，Höfte M ... -  《Environmental Microbiology Reports》

To settle or to move? The interplay between two classes of cyclic lipopeptides in the biocontrol strain Pseudomonas CMR12a.

Pseudomonas CMR12a is a biocontrol strain that produces phenazine antibiotics and as yet uncharacterized cyclic lipopeptides (CLPs). The CLPs of CMR12a were studied by chemical structure analysis and in silico analysis of the gene clusters encoding the non-ribosomal peptide synthetases responsible for CLP biosynthesis. CMR12a produces two different classes of CLPs: orfamides B, D and E, whereby the latter two represent new derivatives of the orfamide family, and sessilins A-C. The orfamides are made up of a 10 amino acid peptide coupled to a β-hydroxydodecanoyl or β-hydroxytetradecanoyl fatty acid moiety, and are related to orfamides produced by biocontrol strain Pseudomonas protegens Pf-5. The sessilins consist of an 18-amino acid peptide linked to a β-hydroxyoctanoyl fatty acid and differ in one amino acid from tolaasins, toxins produced by the mushroom pathogen Pseudomonas tolaasii. CLP biosynthesis mutants were constructed and tested for biofilm formation and swarming motility. Orfamides appeared indispensable for swarming while sessilin mutants showed reduced biofilm formation, but enhanced swarming motility. The interplay between the two classes of CLPs fine tunes these processes. The presence of sessilins in wild type CMR12a interferes with swarming by hampering the release of orfamides and by co-precipitating orfamides to form a white line in agar.

D'aes J ，Kieu NP ，Léclère V ，Tokarski C ，Olorunleke FE ，De Maeyer K ，Jacques P ，Höfte M ，Ongena M ... -  《-》

Sensitivity of Rhizoctonia Isolates to Phenazine-1-Carboxylic Acid and Biological Control by Phenazine-Producing Pseudomonas spp.

Jaaffar AKM ，Parejko JA ，Paulitz TC ，Weller DM ，Thomashow LS ... -  《PHYTOPATHOLOGY》