Elucidating the Functional and Taxonomic Diversity of Soil Microbial Communities From Three Commercial Soybean Farms in South Africa

Prior to the introduction of the exotic inoculant strain of Bradyrhizobium, South African soils lacked the rhizobia that nodulate soybean. Five decades of soybean inoculation practice resulted in the establishment of the Bradyrhizobium population in many soybean growing fields. However, there is no record of the magnitude of this establishment and its impact on the taxonomic and functional abundance of other microbes. Here we use a shotgun metagenomics approach to elucidate the taxonomic and functional profiles of the soil microbes from selected commercial soybean farms in South Africa. Metagenomics of the total sequences revealed that Proteobacteria, Actinobacteria, Firmicutes, Acidobacteria and Bacteroitedes are the prevalent phyla which differed in their relative abundance. Bradyrhizobium was the predominant genus at all three locations. Predicted functions detected genes essential for nitrogen metabolism, including nitrogen fixation, which have been unveiled in this study at a higher rate in all locations investigated. This study uncovers the microbial communities associated with soybean soils in South Africa. The study also generated vital information on the establishment of Bradyrhizobium spp. in the soils of soybean farms, providing a clue on whether inoculation of soya beans is always necessary. The findings, however, warrant further field investigations before any recommendations are rendered.