Exploring the response of Actinobacteria to the presence of phosphorus salts sources: Metabolic and co-metabolic...

This study tested the solubilization of phosphorus by five actinobacterial strains in liquid media containing Ca₃ PO₄ ; AlPO₄ or FePO₄ as the sole phosphate source, and discusses the possible mechanisms involved in this process. P solubilization by different strains was accompanied by a significant drop in pH from 7.0 to 2.15-5.0 after 14 days. The efficiency of different strains depended on the P-source. Streptomyces spp. MM140 and MM141 were the most efficient in solubilizing Ca₃ PO₄ , MM136, and MM141 were the most efficient in solubilizing AlPO₄ , while all strains were equally efficient in solubilizing FePO₄ . Gluconic, oxalic, citric, malic, succinic, formic, and acetic acid were detected in the medium with Ca₃ PO₄ , while all except acetic acid were detected in the media with FePO₄ or AlPO₄ . Although we did not use an organic source of phosphorus in the media, all strains produced acid and alkaline phosphatase. It is concluded from this study that actinobacteria produced multiple organic acids followed by a decrease in the pH to solubilize phosphate salts. As well as producing phosphatase, these microorganisms were found to have different ways of making P available, suggesting an ecological advantage as they form part of soil microbiomes important for plants.