Assessing the amount of released K from minerals in bacterial liquid culture is the main process for screening and isolation of efficient potassium releasing bacteria (KRB). This study was aimed to determine the amount of released K in solution phase or supernatant (SK) as well as microbial biomass K (MBK). Therefore, 20 different bacterial isolates belonging to the 10 bacterial genera (Beijerinckia, Klebsiella, Azotobacter, Pseudomonas, Agrobacterium, Rhizobium, Sphingomonas, Citrobacter, Microbacterium, and Achromobacter) were individually used to inoculate Aleksandrov medium in presence of biotite or muscovite. Our results from in-vitro experiments revealed that the MBK (K in pellet) is more important than in SK. Although some genera such as Azotobacter and Citrobacter released more SK (16 mg/l from biotite and 12.77 mg/l from muscovite, respectively), the Klebsiella isolates with the highest MBK could release an average of 90 mg/l total K. This study indicated that the assimilated K in microbial cells is the main part of K dissolution from minerals. Due to the fast turnover of nutrients in bacterial biomass, it can be concluded that both SK and MBK could be available for plants. It seems that the finding of this research should be considered in the isolation of KRB.
