Impact of Azospirillum brasilense Az39 inoculation on the maize microbiome

MOLINA, R.; MARIN, A; CASSÁN, F.; LARAMA, G; AVILA, A; CONIGLIO, A.; MORA, V; DE SOUZA, E

Congreso; IV REUNIÓN CONJUNTA DE SOCIEDADES DE BIOLOGÍA DE LA REPÚBLICA ARGENTINA; 2020

Azospirillum is one of the most used genera for agriculture worldwide. Inoculation with many plant growth-promoting rhizobacteria (PGPR) modifies the microbial communities associated with plants, but few reports are available for Azospirillum. In order to understand if the A. brasilense Az39 inoculation modifies the bacterial populations associated with maize rhizosphere, we performed a metagenomics analysis under experimental controlled conditions. For this purpose, maize seeds were pre-germinated for 7 days and transplanted to pots containing soil samples obtained from a georeferenced agricultural region of the Córdoba Province (Argentina). The seedlings were inoculated at root level with 100 L of 1×108 cfu/mL of A. brasilense Az39 (inoculated rhizosphere). An equivalent volume of sterile distilled water was added to non-inoculated seedlings (non-inoculated rhizosphere) and non-inoculated soil treated with an equivalent volume of sterile water (bulk soil) were used as control treatments. After 14 days-incubation, the whole DNA was extracted from the rhizosphere, and the V4 region of the bacterial 16S rRNA gene was amplified and sequenced using the Illumina MiSeq platform. The genus relative abundances were evaluated and both alpha and beta diversity were assessed. The microbial differences were explored using LEfSe and IndicSpecies algorithms and a co-occurrence network analysis was performed. Results showed that Azospirillum was the most abundant genus in inoculated samples which confirms its ability to colonize the maize rhizosphere. A significant difference was observed for alpha diversity according to the Pielou index. No differences in the beta diversity between Az39 inoculated and non-inoculated rhizospheres were observed. However, these communities maintained a differential structure in comparison with the bulk soil. According to LEfSe index, the four most abundant genera associated with Az39 were Burkholderia, Massilia, Sphingobium and Cupriavidus, while Azospirillum and Pseudomonas were the most abundant genera according to IndicSpecies. An increase in relative abundance of some members of the Rhizobales order was observed by inoculation of Az39 in the maize rhizosphere. Finally, the co-occurrence network showed a positive interaction between Azospirillum and Pseudomonas genus. The ability of Azospirillum to colonize the maize rhizosphere induced changes in relative abundance of some bacterial genera in the rhizosphere and such changes could involve new interactions between these recruited microorganisms in the microbiome and together with some differential effects on plants.