Response of the microbial community associated with sweet potato (Ipomoea batatas) to Bacillus safensis and Bacillus velezensis strains.

Sweet potato is a subsistence crop cultivated worldwide. Although it is generally considered tolerant to different diseases, it is quite susceptible to the fungus Plenodomus destruens that causes foot-rot disease. Plant growth-promoting bacteria associated with sweet potato remain poorly studied, but some Bacillus strains may have potential as biological control agents. Here, we evaluate the persistence of two bacterial strains-Bacillus safensis T052-76 and Bacillus velezensis T149-19-in pot experiments and assess their impact on indigenous bacterial and fungal communities associated with sweet potato. Numbers of cells of both strains introduced into pots remained stable in the rhizosphere of sweet potato over the 180-day experiment. Denaturing gradient gel electrophoresis based on the rrs gene encoding bacterial 16S rRNA and the fungal ribosomal internal transcribed spacer region showed that bands corresponding to the introduced strains were not detected in plant endosphere. PERMANOVA and non-metric multidimensional scaling statistical analyses showed that: (1) strain T052-76 altered the structure of the indigenous bacterial community (rhizosphere and soil) more than strain T149-19; (2) T052-76 slightly altered the structure of the indigenous fungal community (rhizosphere and soil) and (3) strain T149-19 did not disturb the fungal community. Our results demonstrate the stability of both Bacillus strains in the sweet potato rhizosphere and, apart from the influence of B. safensis T052-76 on the bacterial community, their limited impact on the microbial community associated with this important crop plant.