This study aimed to determine the effect of sulfur (S) application on a root-associated microbial community resulting in a rhizosphere microbiome with better nutrient mobilizing capacity. Soybean plants were cultivated with or without S application, the organic acids secreted from the roots were compared. High-throughput sequencing of 16S rRNA was used to analyze the effect of S on microbial community structure of the soybean rhizosphere. Several plant growth-promoting bacteria (PGPB) isolated from the rhizosphere were identified that can be harnessed for crop productivity. The amount of malic acid secreted from the soybean roots was significantly induced by S application. According to the microbiota analysis, the relative abundance of Polaromonas, identified to have positive association with malic acid, and arylsulfatase-producing Pseudomonas, were increased in S-applied soil. Burkholderia sp. JSA5, obtained from S-applied soil, showed multiple nutrient-mobilizing traits among the isolates. In this study, S application affected the soybean rhizosphere bacterial community structure, suggesting the contribution of changing plant conditions such as in the increase in organic acid secretion. Not only the shift of the microbiota but also isolated strains from S-fertilized soil showed PGPB activity, as well as isolated bacteria that have the potential to be harnessed for crop productivity.

Phosphorus (P) solubilization is one of the major traits for plant growth-promoting rhizobacteria since P is easily rendered insoluble in soil. Phosphate-solubilizing microorganisms can be harnessed as an environment-friendly strategy to enhance the mobilization and acquisition of P by crops. Utilization of such microorganisms as microbial inoculants in agriculture serves as an alternative to chemical fertilizers and an approach for more efficient P fertilization. Hence, this study aims to characterize a phosphate-solubilizing isolate and evaluate its potential as a microbial inoculant. Morphological, biochemical, and genetic characterization of the isolate were performed. Then, the mineral phosphate solubilization ability of the isolate was evaluated. Lastly, this study evaluated the plant growth promotion of the isolate as a single inoculant in rice or as a co-inoculant with rhizobia in peanuts. On the basis of biochemical and 16S rRNA analysis, the isolate was identified as Enterobacter sp. Also, it can solubilize P from tricalcium phosphate or aluminum phosphate. Simultaneous with P solubilization, medium acidification, and gluconic acid secretion were observed. Lastly, the Enterobacter sp. isolate could potentially be developed as a biofertilizer in reducing P resource input or to enhance the performance of a rhizobia inoculant.