Cowpea nodules host a similar bacterial community regardless of soil properties

Abstract Nodulation results of a host-specific association between rhizobia and leguminous plants. However, it has been observed a rich and diverse bacterial community inside nodules. This study assessed the bacterial community in nodule of cowpea grown in sites with distinct soil properties to address the hypothesis that these differences could influence the bacterial community inside the nodules. Soil samples and nodules of cowpea were collected in six different sites from Northeastern, Brazil. There was a different bacterial community structure and composition comparing bulk soil and nodules, with lower diversity in the last. However, the bacterial communities inside the nodules were not different comparing all sites. The bacterial communities found inside the nodules belonged to Proteobacteria (Bradyrhizobium and Rhizobium with 97% and 2.63%, respectively), Actinobacteria (Conexibacter and Amycolatopsis with 0.047% and 0.015%, respectively), and Firmicutes (Bacillus and Salipaludibacillus with 0.042% and 0.040%, respectively). Our analysis also showed that bulk soil and nodules presented 99.3% and 0.03% of exclusive OTUs, respectively, while these pools shared 0.4% of the bacterial groups. These results indicate that cowpea selected a specific bacterial group that colonizes the nodules, and it is not influenced by soil properties.