Isolation and characterization of cellulose-degrading bacteria from the deep subsurface of the Homestake gold mine, Lead, South Dakota, USA
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The present study investigated the cultivable mesophilic (37°C) and thermophilic (60°C) 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 55°C, while for a thermophilic isolate (DUSELR7) they were 5.0 and 75°C, respectively. Furthermore, DUSELG12 retained about 40% CMCase activity after incubation at 60°C for 8 h. Most remarkably, thermophilic isolate, DUSELR7 retained 26% CMCase activity at 60°C up to a period of 300 h. 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.
KeywordsCellulose-degrading bacteria DUSEL Deep subsurface Thermostable enzymes Gold mine
This research was funded by the South Dakota Governor’s program (2010) and Board of Regents grant for project title “Generating Preliminary Microbial Data on Homestake Gold Mine”. In addition, Geetha L. Muppidi acknowledges funding through the SD NASA-EPSCoR Program (NASA Grant # NCC5-588). The support of the SDSM&T’s Department of Chemical and Biological Engineering also contributed significantly to this research. We also would like to thank the anonymous reviewers whose critiques were instrumental in making our manuscript of an excellent quality.
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