Deciphering the role of Bacillus spp. for the sustainable use of phosphorus in agriculta: from bioprospecting to functional gene analysis

Abstract

Phosphorus (P) is a key element for plant growth and development. In tropical regions, this element is strongly bound to the soil matrix. In order to supply plant nutritional requirements, more sustainable management practices are necessary as alternatives to the application of high doses of phosphate fertilizers. In this context, Bacillus spp. have been described as P solubilizing and mineralizing strains. The association between these bacterial strains and arbuscular mycorrhizal fungi (AMF), which are related to higher efficiency P uptake by plants, may promote more significant availability of this nutrient during interaction among Bacillus spp.-AMF-plant. Genetic studies focused on processes such as P solubilization and mineralization by Bacillus spp. are incipient and the effect of these processes in association with AMF at the molecular level is still little known. In this scenario, this project aims to elucidate the mechanisms of P solubilization and mineralization of Bacillus spp. capable of interacting with AMF, contributing to sugarcane and maize growth. We will perform in vitro bioassays to select Bacillus strains with significant profile for P solubilization and mineralization and, in association with AMF Rhizophagus intraradices, optimize P-uptake and growth stimulation of sugarcane and maize. The effect of Bacillus spp.-AMF inoculation in bacterial and fungal communities modulation associated with sugarcane and maize will be investigated by metataxonomy and X-ray fluorescence spectroscopy to understand the effect of inoculation and native microbial community in the condition of highest P accumulation in root and rhizosphere of these crops. Genome of the most promising strains of Bacillus spp. will be sequenced to unravel key genes related to the P cycle of these bacteria and perform comparative genomic studies. The genome editing system CRISPR-Cas9 will be used to generate mutant knock-outs of genes identified as part of metabolic pathways involved in P solubilization and mineralization in Bacillus spp.. This step aims at understanding the role of genes in P solubilization and mineralization by Bacillus spp., as well as their interactions with AMF and the crops sugarcane and maize. By obtaining Bacillus spp. mutants knock-outs in the PhoP/PhoR two-component system and their transcriptome data, it will be possible to understand the function of the regulon related to the presence of P in the environment. The results obtained in this polyphasic approach to the role of Bacillus spp. in P cycle will allow an unprecedented comprehension of the genetic mechanisms involved in P solubilization and mineralization, as well as a better understanding on plant-microorganism interactions from an ecological point of view, contributing to the development of a more sustainable agriculture. (AU)