Solubilização de fósforo por actinobactérias do semiárido brasileiro em diferentes meios de cultura e pó de rocha

Abstract

Phosphorus (P) is one of the essential elements for the growth and development of plants, representing about 0.2% of dry weight. However, phosphorus is not found in nature in its free form, it is unstable as a gas due to its reactivity and is an essential element for life. In soils, phosphorus is present in different forms: soluble, mineral, adsorbed, and organic. Phosphorus-solubilizing microorganisms have the ability to convert insoluble phosphorus compounds into available phosphates, which increase nutrient availability for plants, and several bacterial genera are known for being phosphate solubilizers with the potential to replace conventional chemical fertilizers in agriculture. Among them, actinobacteria have been extensively studied as P solubilizers or as mineralizers. Qualitative and quantitative assays were conducted in NBRIP and VERMA culture media, with and without the addition of rock dust. The quantitative assays involved the growth of actinobacteria in liquid medium, with pH measurements taken at the end of the experiment. The VERMA medium proved to be the most effective for phosphorus solubilization, with isolate B10 standing out with the highest recorded value among all media and isolates (933.90 μg/mL). C8 and C5 showed high solubilization levels (466.02 μg/mL and 392.32 μg/mL, respectively). Isolate J1 had low solubilization (44.70 μg/mL), indicating performance variability depending on the medium used, while the addition of the remineralizer BTGRAN to the NBRIP and VERMA media resulted in reduced solubilization. In NBRIP+BTGRAN, C5 recorded the highest solubilization (166.25 μg/mL). Isolate B10 (63.86 μg/mL), isolate J1 had the lowest value (31.98 μg/mL). In the VERMA+BTGRAN medium, isolate B10 maintained the highest value (94.00 μg/mL) among them. However, C5 and C8 showed drastic drops to (12.97 μg/mL) and (3.67 μg/mL), respectively, while J1 reached (48.91 μg/mL). In the qualitative analysis of phosphate solubilization, it was observed that the actinobacterial isolates did not show significant efficiency in solid NBRIP medium or NBRIP supplemented with the remineralizer BTGRAN. This suggests that the choice of culture medium and the presence of additives can significantly influence the effectiveness of actinobacteria in phosphorus solubilization.