Isolation and Characterization of Basidiomycetous Yeasts Capable of Producing Phytase under Oligotrophic Conditions

Phytic acid is an organic phosphorus source naturally produced by plants as phosphorus stock and can be an alternative to rock phosphate, which is a dwindling resource globally. However, phytic acid is insoluble, owing to its binding to divalent metals and is, thus, not readily bioavailable for plants and monogastric livestock. Therefore, the enzyme phytase is indispensable for hydrolyzing phytic acid to liberate free phosphates for nutritional availability, making the screening of novel phytase-producing microbes an attractive research focus to agriculture and animal feed industries. In the present study, a soil-extract-based culture medium was supplemented with phytic acid as the sole phosphorus source and oligotrophic phytase-producing strains, which had not been previously studied, were isolated. Four fungal strains with phytic acid, assimilation activities were isolated. They were found to produce phytase in the culture supernatants and phylogenetic analysis identified three strains as basidiomycetous yeasts (Saitozyma, Leucosporidium, and Malassezia) and one strain as an ascomycetous fungus (Chaetocapnodium). The optimal pH for phytase activity of the strains was 6.0-7.0, suggesting that they are suitable for industrial applications as feed supplements or fertilizer additives for farmland.