Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/8/2009
Publication Date: 2/3/2009
Citation: Rastogi, G., Muppidi, G.L., Gurram, R.N., Adhikari, A., Bischoff, K.M., Hughes, S.R., Apel, W.A., Bang, S.S., Dixon, D.J., Sani, R.K. 2009. Isolation and characterization of cellulose-degrading bacteria from the deep subsurface of the Homestake Gold Mine, Lead, South Dakota, USA. Journal of Industrial Microbiology and Biotechnology. 36:585-598. Interpretive Summary: New microorganisms that degrade cellulose are needed to improve the efficiency of converting low-value agricultural and forestry residues into valuable fuels and chemicals. In the present study, soil-like samples from the deep subsurface of the Homestake gold mine in Lead, South Dakota were screened for bacteria that could grow on cellulose. A variety of bacterial types were isolated, some that could grow at high temperatures. One strain was found to produce a cellulose-degrading enzyme that was active at 75°C and stable for 300 hours. Results will be valuable to researchers developing new enzymes to serve as biocatalysts in the conversion of agricultural residues to fermentable sugars.
Technical Abstract: The present study investigated the cultivable mesophilic (37ºC) and thermophilic (60ºC) cellulose-degrading bacterial diversity in a weathered soil-like sample collected from the deep subsurface (1.5 km depth) of the Homestake gold mine in Lead, South Dakota, USA. Chemical characterization of the sample by X-ray fluorescence spectroscopy revealed a high amount of toxic heavy metals such as Cu, Cr, Pb, Ni, and Zn. Molecular community structures were determined by phylogenetic analysis of 16S rRNA gene sequences retrieved from enrichment cultures growing in presence of microcrystalline cellulose as the sole source of carbon. All phylotypes retrieved from enrichment cultures were affiliated to Firmicutes. Cellulose degrading mesophilic and thermophilic pure cultures belonging to the genera Brevibacillus, Paenibacillus, Bacillus, and Geobacillus were isolated from enrichment cultures, and selected cultures were studied for enzyme activities. For a mesophilic isolate (DUSELG12), the optimum pH and temperature for carboxymethyl cellulase (CMCase) were 5.5 and 55ºC, while for a thermophilic isolate (DUSELR7) they were 5.0 and 75ºC, respectively. Furthermore, DUSELG12 retained about 40% CMCase activity after incubation at 60ºC for 8 hours. Most remarkably, thermophilic isolate, DUSELR7 retained 26% CMCase activity at 60ºC up to a period of 300 hours. Overall, the present work revealed the presence of different cellulose degrading bacterial lineages in the unique deep subsurface environment of the mine. The results also have strong implications for biological conversion of cellulosic agricultural and forestry wastes to commodity chemicals including sugars.