Amending metagenomic bacterial community in soybean-cultivated soils to enhance phytoestrogen in soybean roots by communicating with mixture of culturable rhizospheric bacteria

The amendment of metagenomic bacterial community in soybean-cultivated soils to enhance phytoestrogen levels in soybean roots through communicating with mixture of culturable rhizospheric bacteria (RB) were rarely studied. RB from soybean roots and soybean-cultivated soils were isolated and applied to soybean plants. Treated soybean plants were divided into three groups: control (CTL), soybean root RB (SRR), and soybean-cultivated soil RB (SSR). Each group had a distinct influence on the metagenomic bacterial community of the soybean rhizosphere. The α-proteobacteria were the dominant class in all three groups, although SRR was enriched with Actinomycetes, Fimbriimonadia, and γ-proteobacteria, while SSR was enriched with Bacilli, Chitinophagia, and Gemmatimonadia classes. Additionally, at the significantly species level, SRR was enriched with Arthrobacter sp. and Azospirillum lipoferum, while SSR was enriched with Bradyrhizobium sp. and Rhizobium sp. Moreover, the RB treatment significantly affected the root metabolite composition. In the SSR-treated group, phenylalanine (18.80-47.81 mg/100 g) and tyrosine (8.03-21.98 mg/100 g) tended to be significantly enhanced. Additionally, secondary metabolites, such as isoflavones, total phenolics, and total flavonoids, were also significantly affected by the RB treatment; secondary metabolites were the highest in the SSR-treated group. These changes in metabolites also affected radical scavenging activities, with the SSR-treated group displaying significantly increased activities compared to the other groups. As a result, DPPH increased from 32.44 % to 47.21 % and ABTS from 53.41 % to 74.23 %. Therefore, RB treatment can influence the bacteria and root metabolite compositions within the soybean rhizosphere, revealing its potential applications in soybean productivity.