Inoculation with carbofuran-degrading rhizobacteria promotes maize growth through production of IAA and regulation of the release of plant-specialized metabolites

Abstract

Toxic residues of the insecticide carbofuran in farmland is an urgent problem, and high concentrations of carbofuran have been found in the rhizoshperic soil of maize treated with seed coating agents 120–180 days after planting. Using an enrichment co-culture method, we identify a bacterial strain obtained from these carbofuran-contaminated rhizosphere soils as Leclercia adecarboxylata MCH-1. This strain exhibited a significant ability to degrade both carbofuran and 3-keto carbofuran, with total degradation of 55.6 ± 4.6% and 75.7 ± 3.4%, respectively, 24 h following start of co-culture. Further activity screening revealed that the inoculation of maize roots with L. adecarboxylata MCH-1 promoted maize seedling growth. Quantitative analysis demonstrated that this bacterial strain had the ability to synthesize the phytohormone IAA. Simultaneously, the concentration of IAA in the rhizospheric soil increased following inoculation of maize roots with L. adecarboxylata MCH-1. Moreover, the concentrations of plant specialized metabolites, including phenolics, terpenoids, and alkaloids, decreased in maize seedlings and were elevated in the rhizospheric soil after maize roots had been inoculated with the MCH-1 strain. Interestingly, the growth of the strain MCH-1 was improved by co-culture with root exudates obtained from the rhizospheric soil, specifically 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, and zealexin A1 (ZA1). Taken together, our results suggest that the carbofuran-degrading rhizobacterium L. adecarboxylata MCH-1 is able to interact with maize plants through the regulation of maize root exudates. Moreover, inoculation with L. adecarboxylata MCH-1 promotes maize growth through the production of IAA and regulation of the release of plant specialized metabolites. Our results provide a new model organism for the remediation of farmland soils from pollution with carbofuran residues.