Bacillus methylotrophicus isolated from the cucumber rhizosphere degrades ferulic acid in soil and affects antioxidant and rhizosphere enzyme activities

Ferulic acid (FA) accumulates in soil and inhibits plant growth. We examined whether the FA-degrading bacterium Bacillus methylotrophicus degrades FA in soil. B. methylotrophicus strain CSY-F1 was isolated and applied to unplanted soil and soil planted with Cucumis sativus (cucumber). We analyzed the effects of B. methylotrophicus on rhizosphere enzyme activities and antioxidant enzyme activities in cucumber and CSY-F1 exposed to FA. CSY-F1 degraded FA in culture medium and in soil, giving rise to 4-vinyl guaiacol, vanillin, vanillic acid, and protocatechuic acid. When cucumber seedlings were grown in soil treated with FA, the activities of some soil enzymes decreased, and the malonaldehyde content in cucumber leaves increased. The addition of CSY-F1 to FA-treated soil increased the activities of these soil enzymes, decreased the FA concentration in the soil, and elevated the activities of some antioxidant enzymes in seedlings. Moreover, the levels of superoxide radical, hydrogen peroxide, and malonaldehyde were reduced in cucumber leaves. FA treatment increased the activities of antioxidant enzymes, including superoxide dismutase, catalase, and monodehydroascorbate, in CSY-F1. Bacillus methylotrophicus CSY-F1 has potential applications as an FA-degrading agent in soil, as it mitigates FA stress in cucumber seedlings by activating several antioxidant and soil enzymes.