Metatranscriptomics and nitrogen fixation from the rhizoplane of maize plantlets inoculated with a group of PGPRs

The free-living soil bacteria that are beneficial for the growth of plants are known as plant growth-promoting rhizobacteria (PGPR). In this work, a multi-species of PGPR bacteria inoculant was designed, which included nitrogen-fixing strains such as Rhizobium phaseoli, Sinorhizobium americanum and Azospirillum brasilense, as well as other plant growth promoting bacteria such as Bacillus subtillis and Methylobacterium extorquens. The multi-species community exerted a beneficial effect on plant seedlings when it was inoculated, greater than the effect observed when inoculating each bacteria individually. Acetylene reduction of maize roots was recorded with the multi-species inoculant, which suggests that nitrogen fixation occurred under these conditions. To analyze the contributions of the different nitrogen-fixing bacteria that were inoculated, a metatranscriptomic analysis was performed. The differential expression analysis revealed that the predominantly nif transcripts of Azospirillum are overexpressed, suggesting that it was responsible for nitrogen fixation in maize. Overall, we analyzed the interaction of a synthetic community, suggesting it as an option, for future formulations of biofertilizers.\n\nIMPORTANCEWhile nodulation processes and nitrogen fixation by rhizobia have been well studied, little is known about the interaction between rhizobia and non-leguminous plants such as maize, which is used as a model for this study. Nitrogen fixation in cereals is a long searched goal. Instead of single species inoculants, multi-species inoculation may be more efficient to promote plant growth and fix nitrogen. Metatrascriptomes allowed us to recognize the bacteria responsible for nitrogen fixation in plant rootlets. The study of the function of certain genes may help to understand how microorganisms interact with the root plant, as well as allow a better use of microorganisms for the generation of novel biofertilizers using microbial consortia.