Pretreatment of fibrous biomass and growth of biosurfactant-producing Bacillus subtilis on biomass-derived fermentable sugars
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Pretreatment of six fibrous biomasses (switchgrass, alfalfa, soy hulls, soy fiber, DDGS and Baggase) and subsequent hydrolysis using cellulolytic enzymes at a 2.5 % (v/v) and 5 % (v/v) loading 2.5 (v/v) and 5 % (v/v) loading was compared for higher amounts of sugars released. Soaking of biomasses of switchgrass, alfalfa, soy hulls and bagasse in 15 % w/w ammonia was optimal at 60 °C for 12 h, followed by enzymatic hydrolysis, yielding 72, 70, 80 and 75 % carbohydrate conversions, respectively. However, soaking in ammonia was not needed for soy fiber and DDGS as these contained very little lignin. Ultrasonication for 3 min @ 100 % amplitude (170 µM) was found to be optimal for soy fiber and DDGS from which 77 and 83 % carbohydrate conversion, respectively, was obtained following enzyme treatment at 5 % (w/v) enzyme. The sugars released by enzymatic hydrolysis of pretreated biomass were utilized as an energy source by Bacillus subtilis in fermentation media at 2 % (w/v) of concentration. In shake flask trials, cell growth was 15–20 % higher on hydrolysates of ammonia-treated switchgrass and alfalfa vs. glucose-based control media due to the presence of a wider range of monomeric sugars (glucose, xylose, arabinose, mannose and galactose). In contrast, growth was less on soy hull hydrolysates prepared with ammonia pretreatment.
KeywordsBiomass pretreatment Biosurfactants Liquid ammonia Ultrasonication Enzymatic hydrolysis Bacillus subtilis
The authors would like to acknowledge the financial support for this research provided by Environmental Protection Agency (EPA) for their grant (award # 83518101).
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