A Modified Method to Assess the Potential of Bacteria for Potassium Release from Mica Minerals

A substantial proportion of soil potassium (K) is structurally bound within silicate minerals and is unavailable for plant uptake. Potassium-releasing bacteria (KRB) can sustainably mobilize mineral-bound K, but their identification is constrained by conventional Aleksandrov-based screening. This study evaluated the conventional Aleksandrov assay and developed a modified culture medium to assess bacterial K-release potential. Six KRB strains were evaluated in solid and liquid culture media containing white mica (muscovite) and black mica (biotite) as the sole K source under a completely randomized design with three replicates. Halo formation on conventional solid Aleksandrov medium resulted primarily from dissolution of insoluble phosphorus compounds rather than K release from silicate minerals, leading to erroneous estimates of K-mobilizing capacity. In contrast, the modified liquid medium, designed to eliminate nutritional limitations, significantly enhanced K release by all strains. Statistical analyses identified culture medium composition as the dominant determinant of K mobilization, exerting stronger effects than bacterial strain, mineral type, or incubation period. Significant interaction effects demonstrated that K release is governed by the interplay among microbial traits, mineralogy, and culture conditions. These findings demonstrate the limitations of conventional halo-based screening and establish a robust, reproducible platform for reliable identification and quantitative evaluation of high-performing KRB.