Degraded soils in the Brazilian semiarid region harbor bacteria with high phosphate solubilization potential

ABSTRACT The widespread deficiency of available phosphorus (P) in soils, particularly in tropical regions, necessitates the application of phosphate fertilizers due to their high adsorption. However, excessive use engenders significant economic costs and contributes to eutrophication of aquatic ecosystems and the mobilization of heavy metals. One viable alternative is the use of phosphate-solubilizing bacteria (PSB), which can solubilize phosphate through the production of acids and enzymes. This study aimed to assess the cultivable PSB community in different pedogenetic horizons of degraded and preserved Planosols and Luvisols (Planossolos and Luvissolos) in the semiarid and subhumid regions of Brazil, as these soils exhibit a high P availability, particularly in deeper layers. Furthermore, the biotechnological potential of the most promising PSB was evaluated in corn. A total of 170 PSB strains were collected, with 96 bacteria isolated from Planosol and 74 from Luvisol. The majority of the PSB exhibited a medium solubilization index and a broad morphophysiological diversity, and all solubilized calcium phosphate in liquid media. To investigate the biotechnological potential of these bacteria, eight PSB strains were selected based on their ability to solubilize calcium phosphate (>160 mg L-1) and to promote plant growth through mechanisms such as high auxin production, exopolysaccharide synthesis, zinc solubilization, and antagonism against the pathogen Fusarium sp. The PSB were identified as follows: PL1A, PL2L (Priestia sp.), PL1B (Neobacillus sp.), PL3J and LU13C (Streptomyces sp.), PL6A (Fictibacillus sp.), and PL18E and LU10E (Bacillus sp.). The PSB were inoculated into corn with the treatments based on the absence of phosphorus (-P) (control), simple superphosphate (SSP), reactive natural phosphate (RP), and the SSP + RP combination. The maximum available P value in the soil was observed in the RP treatment, where LU10E (78.70 mg dm-3) was inoculated, and in the SSP treatment, where LUC13C (69.9 mg dm-3) was inoculated. Isolates LU13C, LU10E, and PL3J exhibited the highest efficiency in phosphorus mobilization, PL1B and PL18E were moderately efficient, while PL1A, PL2L, and PL6A were the least efficient. This study assessed the diversity of phosphate-solubilizing bacteria (PSB) across soil profiles of degraded and vegetated Planosols and Luvisols in the Borborema Province, Northeastern Brazil, resulting in the establishment of the first bacterial collection comprising 170 strains with confirmed potential for phosphorus solubilization and corn growth promotion.