Exploiting of honey-associated Bacillus strains as plant-growth promoting bacteria for enhancing barley growth in rare earth tailings

Abstract

In the coming decades, exploitation of plant growth promoting bacteria (PGPB) will be a major trend in sustainable agriculture. Except for rhizobacteria, the bacteria inhabiting the non-rhizosphere could be considered the supplementary microbial source to exploit PGPB. Rare earth tailings soil (RETS) has caused a serious threat to sustainable agriculture due to excessive aluminum (Al) toxicity under acidic condition (pH < 5.5). The efficient restoration strategy is to combine phytoremediation and PGPB. The aim of this work was to screen honey-associated Bacillus strains as PGPB to improve barley (Hordeum vulgare L.) growth in RETS. Nine Bacillus strains from honey were initially selected with higher tolerance to acid (pH 4.0) and Al stress (1.5 mM). Only six strains among these nine strains could produce ACC deaminase. The nine strains were all efficient in dissolving phosphate, producing organic acid, siderophore, and IAA. The nine strains could promote barley seedlings growth mainly via production of organic acid, ACC deaminase. However, this growth promotion was weakened slightly by siderophore and phosphate solubilization under acidic condition. On the whole, inoculation with the nine strains obviously enhanced barley seedlings growth in RETS. Thus, the nine honey-associated Bacillus strains could be exploited as PGPB to enhance barley growth in RETS.