Isolation of sulfate tolerant mutants of Clostridium tyrobutyricum using gamma-ray irradiation

Isolation of sulfate tolerant mutants of Clostridium tyrobutyricum using gamma-ray irradiation
sulfate tolerance; butyric acid; C. tyrobutyricum; lignocellulose; gamma-ray irradiation
Issue Date
International Biotechnology Symposium and Exhibition
Global investment to renewable energy is continuously increased as global petroleum resources continue to be declined. Biomass resource is highly regarded because it can be used as a feed stock for microbial production of biofuels and biochemicals. Lignocellulosic biomass is the most abundant renewable resource in the world. However, lignocellulose needs to be pretreated into usable monosaccharides before fermentation. The dilute sulfuric acid pretreatment can achieve high reaction rates and significantly improve cellulose hydrolysis. However, the neutralization of sulfuric acid was needed due to sulfuric acid inhibited microbial fermentation. The addition of Ca(OH)2 and CaCO3 to neutralize the sulfuric acid is a conventional operation that complicates pretreatment process and produces large amounts of gypsum which was normally dumped as waste. All the extra expense and operations can be reduced if microbes are able to grow and metabolize in presence of high concentration of sulfate. In this study, we describe the use of gamma-ray irradiation for improved sulfate tolerance by C. tyrobutyricum ATCC 25755. After two rounds of gamma-ray irradiation, three strains that could grow in presence of 40 g/L of sulfate were obtained. We observed 3.2- and 4.6-fold increases in cell growth and butyric acid production in presence of 40 g/L of sulfate, respectively. In case of lignocellulosic hydrolysate without gypsum treatment, the mutated strain produced 7.9 g/L of butyric acid but wild type was not grown after 48 hour of fermentation.
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