Mycin and peptin lipopeptides are major contributors to the biocontrol of Sclerotinia sclerotiorum by Pseudomonas mediterranea

Abstract

The fungal pathogen Sclerotinia sclerotiorum is the causal agent of the white mold disease in several economically important crops. Control methods are currently limited to the use of synthetic fungicides and resistance to these fungicides is increasing. Biological control may prove to be a more sustainable control strategy for this disease, as well as other fungal diseases. In a previous study, our team identified Pseudomonas strains that can reduce white mold symptom severity in lettuce. The exact mechanisms underlying this biocontrol were not explored, but the biocontrol activity of these Pseudomonas strains strongly correlated with the presence of three gene clusters involved in the biosynthesis of the lipopeptides brabantamides, corpeptin, and thanamycin. In this study, to better understand the mechanisms at play and progress towards the development of a Pseudomonas-based biocontrol inoculant against S. sclerotiorum, key genes involved in the biosynthesis of these lipopeptides were knocked out in the genome of P. mediterranea B21-060. The impact that the loss of function had on the ability of P. mediterranea to inhibit the growth or S. sclerotiorum in vitro and control white mold development in planta was evaluated. Production of corpeptin and thanamycin by P. mediterranea was required to repress the growth of S. sclerotiorum and suppress white mold symptom development in lettuce. Furthermore, corpeptin and thanamycin were also identified as key inhibitory molecules against Botrytis cinerea and Rhizoctonia solani, two other important fungal pathogens. This study highlights the potential of corpeptin and thanamycin in Pseudomonas-mediated control of different fungal plant diseases.