Modulation of Maize Rhizosphere Microbiota Composition by Inoculation with Azospirillum argentinense Az39 (Formerly A. brasilense Az39)

Azospirillum is one of the most important plant growths promoting rhizobacteria used in agriculture worldwide. However, few reports are available describing the effects of this bacterial genus on the inoculated plant microbiome. In order to determine whether A. argentinense inoculation modifies the bacterial microbiota associated with the maize rhizosphere, we performed a high-throughput 16S rRNA gene sequence analysis under experimental controlled conditions. Rhizosphere metagenomic DNA was obtained from plants inoculated and non-inoculated with A. argentinense Az39, and bulk soil was used as a reference treatment. Biodiversity, microbial community composition, co-occurrence network and predicted function analyses (FAPROTAX) were performed. Azospirillum was the most abundant genus occurring in the rhizosphere of inoculated plants. Regarding the alpha diversity, a significant reduction in the bacteria evenness was observed in the inoculated rhizosphere. The beta diversity analysis showed a differential structure of the communities of each treatment. According to the LEfSe index, the three most abundant genera associated with Az39 inoculation were Burkholderia , Massilia and Sphingobium . An increase in the relative abundance of some members of the Hyphomicrobiales (ex Rhizobiales ) order was observed in inoculated plants. Co-occurrence networks showed a positive interaction between Azospirillum and Pseudomonas and a negative correlation with Hyphomicrobium . The FAPROTAX analysis associated Azospirillum inoculation with some functions related to chemoheterotrophy, phototrophy and the nitrogen cycle. Our results allowed us to conclude that Azospirillum is able to colonize the maize rhizosphere after inoculation and that this colonization process induces an increase in the relative abundance of beneficial bacterial genera, also commonly used as biofertilizers in agriculture.