Isolation and Characterization of Coal Solubilizing Aerobic Microorganisms from Salt Range Coal Mines, Pakistan

Microbial solubilization of coal has been considered as a promising technology to convert raw coal into valuable products. In the present study, initially a total of 50 different aerobic bacterial and fungal isolates have been isolated from soil, coal and water samples of Dulmial Coal Mines, Chakwal, Pakistan, but on the basis of solubilization potential, only four isolates were selected for further study. The intensity of biosolubilization was measured by determining the weight loss of the coal pieces, which was observed to be about 25.93% by Pseudomonas sp . AY2, 36.36% by Bacillus sp . AY3 and 50% by Trichoderma sp . AY6, while Phanerochaete sp . AY5 showed maximum coal solubilization potential i.e. 66.67% in 30 days. UV/Vis spectrum revealed an increase in the pattern of absorbance of all treated samples compared to control referring to solubilization. Fourier transform infrared spectroscopy indicated alterations in the structure of treated coal in comparison to control coal suggesting breakdown in the complex structure of coal. The major absorbance bands in infrared spectroscopy for solubilization product were attributed to carbonyl (1,600 cm ⁻¹), hydroxyl (3,450 cm ⁻¹), cyclane (2,925 cm ⁻¹), ether linkage (1,000–1,300 cm ⁻¹), carboxyl (3,300–2,500 cm ⁻¹) and side chains of aromatic ring (1,000–500 cm ⁻¹). The presence of microorganisms and surface erosion of coal residues compared to control samples were observed by scanning electron microscopy, which suggested that isolated microorganisms were able to survive in coal for a longer period of time. Therefore, the present study concluded that microorganisms isolated from coal mines have excellent potential for coal solubilization which is considered as a crucial step in coal methanogenesis allowing them to be used successfully for in situ methane production to meet future energy demands.