Bioprospecção de bactérias solubilizadoras de fosfato e tolerantes a estresse hídrico em solos dos Campos Gerais do Paraná (Brasil)

Abstract

The rhizosphere is the region of soil in close contact with plant roots, characterized by intense microbial activity due to the presence of root exudates. Plant Growth-Promoting Rhizobacteria (PGPR) play a crucial role in enhancing plant growth and development through various mechanisms, such as phosphorus (P) solubilization, production of plant hormones, nitrogen fixation, protection against phytopathogens, and mediation of resistance to biotic and abiotic stresses. In the context of climate emergencies, isolating and characterizing PGPR capable of maintaining growth-promoting activities under abiotic stress conditions, particularly water and osmotic stress, has become an essential technological strategy.The objective of this study was to characterize the mechanisms involved in plant growth promotion by rhizobacteria isolated from maize (Zea mays) cultivated in three native grassland soils with different land-use histories (preservation area, restoration area, and agricultural area). Forty strains were selected

for their efficiency in growing in sorbitol-containing medium, along with the presence of P- solubilization halos in the shortest time and tolerance to osmotic stress. Among the identified

isolates, the genera Pseudomonas and Enterobacter were prominent, with the highest number of representatives. Siderophore production was detected in 26 of these isolates. Phosphorus solubilization was evaluated in liquid medium + Ca3(PO4)2, where Pseudomonas strains stood out, with solubilization indices ranging from 149.3 to 204.2 mg/L after 72 hours of incubation. Osmotic stress tolerance was assessed by measuring bacterial growth at different concentrations of PEG 6000 (11%, 21%, and 26%), with the highest values observed at 11% PEG 6000. Additionally, indole-3-acetic acid (IAA) production was detected in 36 of the 40 strains, indicating the potential of these bacteria to promote plant growth even under osmotic stress conditions. Furthermore, 33 isolates produced exopolysaccharides (EPS), and only one isolate did not produce biofilm in TSB medium. Based on phenotypic analyses, isolates were selected for greenhouse experiments (ongoing). These findings underscore the biotechnological potential of native bacteria for plant growth promotion, highlighting their relevance for use in both agroecosystems and active ecological restoration strategies.