Inoculation of Bacillus megaterium strain A14 alleviates cadmium accumulation in peanut: effects and underlying mechanisms

Aims: A cadmium (Cd)-tolerant Bacillus megaterium strain A14 was used to investigate the effects and mechanisms of bacterial inoculation on peanut growth, Cd accumulation in grains and Cd fixation in Cd-contaminated soil. Methods and Results: Spectroscopic analysis showed that A14 has many functional groups (-OH, -NH2 and -COO et al.) distributed on its surface. The pot experiment indicated that compared to the Cd-contaminated soil alone treatment, inoculation with strain A14 increased shoot and root biomass by 59.93 and 58.31% respectively. The accumulation of Cd in grains decreased by 48.14%, while the proportion of exchangeable Cd in soil decreased from 40 to 26% in A14 inoculated soil. Conclusions: Inoculation with B. megaterium A14 improved peanut plant growth via (i) adsorbing Cd2+ through functional groups on cell surface, (ii) immobilization of Cd in soil through extracellular secretions, (iii) scavenging the reactive oxygen species through production of antioxidant enzymes, and (iv) by reducing the phytoavailable Cd through regulation of Cd transport gene expression. Significance and Impact of the Study: This study provided a new sight on microbial approach for the chemical composition transformation of soil Cd and associated food safety production, which pointed out an efficient way to improve peanut cultivation.