Grey mould control by oxalate degradation using non-antifungal Pseudomonas abietaniphila strain ODB36

Grey mould is an important necrotrophic fungal pathogen that causes huge economic losses in agriculture. Many types of bacteria are used for biological control of grey mould via competition for space or nutrients and/or the production of antifungal metabolites. Oxalate is a key component of virulent necrotic fungal pathogens. In this study, we isolated non-antifungal oxalate-degrading bacteria (ODB) from the surfaces of oxalate-rich spinach and strawberries to investigate their ability to control necrotic fungal pathogens such as grey mould. A total of 36 bacteria grown on oxalate minimal (OM) agar plates were tested for oxalate-degrading activity. Five isolates exhibiting the highest oxalate degradation activity were subjected to molecular identification using 16S rRNA gene sequencing. Two isolates exhibiting non-antifungal activity were subjected to disease suppression assays using Arabidopsis-Botrytis systems. The isolate Pseudomonas abietaniphila ODB36, which exhibited significant plant protective ability, was finally selected for further investigation. Based on whole-genome information, the pseudomonad oxalate degrading (podA) gene, which encodes formyl-CoA transferase, was analysed. The podA-mutant did not inhibit Botrytis infection and oxalate toxicity; the defects were recovered by podA complementation. Purified PodA-His converted oxalate to formate and eliminated oxalate toxicity. These results indicate that P. abietaniphila ODB36 and PodA enzyme are associated with various aspects of grey mould disease inhibitory effects.