Abstract
According to the obtained results, it was established that two strains from five hydrocarbon-destroying bacteria tested on coal – Acinetobacter pitti. RKB1 and Bacillus sp. RKB2 that can solubilize purebrown and pre-treated with nitric acid coal. It was established that 25-28% of raw coal was dissolved indry weight within 30 days. Pretreatment of coal with nitric acid increased the efficiency of this processby 52% when Bacillus sp. RKB2 used. The extracellular solubility of coal with the usage of microbialstrains decreased pH slightly, which indicates the contribution of some alkaline substances to the dissolution of lignite. However, the biosolubilization mechanisms of lignite of two strains were different.These can be either active extracellular substances that synthesized with Acinetobacter pitti. RKB1 or itcan be some enzymes yielded with Bacillus sp. RKB2. Elemental analysis of coals that pretreated withHNO3 and biosolubilization products formed under the action of Acinetobacter pitti. RKB1, or Bacillussp. RKB2 showed significant differences between lignite and products that formed during the microbialconversion of coal.Key words: Lignite, leonardite, biosolubilization.