Presence of glucose, xylose, and glycerol fermenting bacteria in the deep biosphere of the former Homestake gold mine, South Dakota

Abstract

Eight fermentative bacterial strains were isolated from mixed enrichment cultures of a composite soil sample collected at 1.34km depth from the former Homestake gold mine in Lead, SD, USA. Phylogenetic analysis of their 16S rRNA gene sequences revealed that these isolates were affiliated with the phylum Firmicutes belonging to genera Bacillus and Clostridium. Batch fermentation studies demonstrated that isolates had the ability to ferment glucose, xylose, or glycerol to industrially valuable products such as ethanol and 1,3-propanediol (PDO). Ethanol was detected as the major fermentation end product in glucose-fermenting cultures at pH 10 with yields of 0.205-0.304g of ethanol/g of glucose. While a xylose-fermenting strain yielded 0.189g of ethanol/g of xylose and 0.585g of acetic acid/g of xylose at the end of fermentation. At pH 7, glycerol-fermenting isolates produced PDO (0.323-0.458g of PDO/g of glycerol) and ethanol (0.284-0.350g of ethanol/g of glycerol) as major end products while acetic acid and succinic acid were identified as minor by-products in fermentation broths. These results suggest that the deep biosphere of the former Homestake gold mine harbors bacterial strains which could be used in bio-based production of ethanol and PDO. © 2013 Rastogi, Gurram, Bhalla, Gonzalez, Bischoff, Hughes, Kumar and Sani.