Co-Inoculation of Bacillus velezensis Strain S141 and Bradyrhizobium Strains Promotes Nodule Growth and Nitrogen Fixation

The objective of this research was to evaluate the PGPR effect on nodulation and nitrogen-fixing efficiency of soybean ( max (L.) Merr.) by co-inoculation with USDA110. Co-inoculation of S141 with USDA110 into soybean resulted in enhanced nodulation and N2-fixing efficiency by producing larger nodules. To understand the role of S141 on soybean and USDA110 symbiosis, putative genes related to IAA biosynthesis were disrupted, suggesting that co-inoculation of USDA110 with S141Δ reduces the number of large size nodules. It was revealed that may play a major role in IAA biosynthesis in S141 as well as provide a major impact on soybean growth promotion. The disruption of genes related to cytokinin biosynthesis and co-inoculation of USDA110 with S141Δ reduced the number of very large size nodules, and it appears that IPI might play an important role in nodule size of soybean- symbiosis. However, it was possible that not only IAA and cytokinin but also some other substances secreted from S141 facilitate to trigger bigger nodule formation, resulting in enhanced N2-fixation. Therefore, the ability of S141 with Bradyrhizobium co-inoculation to enhance soybean N2-fixation strategy could be further developed for supreme soybean inoculants.