Phosphorus Solubilization by Actinobacteria from Brazilian Semiarid in Different Culture Media and Rock Dust

Phosphorus (P) is an essential mineral macronutrient for maintaining plant growth and development. Plants absorb phosphorus in the form of inorganic phosphate; however, it is one of the macronutrients available in minimal amounts in the soil and is considered a limiting element under specific conditions due to its high reactivity with metals, combined with factors such as soil pH and composition. Phosphate-solubilizing microorganisms (PSMs) play an important role in supplying phosphorus to plants, as they are capable of solubilizing insoluble phosphates—either added or already present in the soil—through processes such as acidification, chelation, and ion exchange reactions. Qualitative and quantitative assays were conducted in NBRIP and VERMA culture media with and without the addition of rock powder. The quantitative assays involved the growth of actinomycetes in liquid media, with pH measurements performed at the end of the experiment. The VERMA medium proved to be the most effective for phosphorus solubilization, whereas the addition of the remineralizer BTGRAN to the NBRIP and VERMA media often resulted in a reduction in solubilization. This suggests that the choice of growth medium and the presence of additives can significantly influence the effectiveness of actinobacteria in phosphorus solubilization.