Screening Of Acetone-butanol Producing Strains And Butanol Production With Corn Cob Hydrolyzate

Fossil fuel is a non-sustainable resource, with the sharp decline in petroleum storage,energy poverty has been a macro-strategic issue for every nation. Consequently, it is animperative task to look for renewable resources. Biobutanol is a potential alternative as it hasseveral advantages such as high energy content, lower water absorption, lower volatility andbetter blending ability. However, conventional materials for butanol fermentation are cerealslike corns, they have many problems such as high cost and competing for food with people.Using non-food biomass like cellulose to ferment butanol can not only gre atly reduce theproduction cost, but utilize waste biomass and avoid the food crises. In this paper, a strain ofClostridium beijerinckii G-23screened from the nature was used to produce butanol withhydrolyzate of corn cob.205acetone-butanol producing strains were screened from133forest soil samples,among which strain G-23was able to use glucose, xylose and the mixture of both to produceacetone and butanol, and butanol yield of the three substrates above were12.6g/L,10.53g/Land10.09g/L, while total solvents were18.9g/L，17.6g/L and16.5g/L. The colony color ofstrain G-23was golden yellow, the strain was identified as Clostridium beijerinckii by16SrDNA analysis, physiological and biochemical tests.Pretreated by levigation, the enzymatic hydrolysis of corn cobs was promoted efficiently,and the reducing sugar concentration in the hydrolyzate was increased by65%compared withthe control group. Coupling levigation pretreatment with enzymatic hydrolysis, the hydrolysiscycle was shortened by58%, reduced from the original66hours to28h. By furtherexperiments, the optimal enzymatic hydrolysis condition was confirmed: the concentrations ofcellulase and xylanase by one gram corn cob were11.25FPU and2505U, respectively. WhenpH was5.0and temperature was50℃, concentration of total reducing sugars, which includedglucose, xylose, arabinose, galactose, mannose and fructose, reached76.3g/L; andconcentrations of glucose and xylose were38.9g/L and34.4g/L, respectively.Pretreated by levigation, enzymatic hydrolyzate of the non-detoxificated corn cobs wasused by G-23to produce butanol, and these results were found: butanol yield reached7.6g/L,total solvents yield reached12.8g/L, utilization rate of reducing sugars reached90.1%,wherein utilization rate of glucose and xylose was95.6%and83.9%, respectively. Butanolproduction could be strongly inhibited by the autoclaved enzymatic hydrolyzate or hydrolysisresidues. Ammonium acetate could promote production of solvents, when added with0.3%（w/v） of ammonium acetate, the butanol yield and total solvents yield was improved by15.6%and18.3%, respectively.The culturing condition of P2medium was optimized and the result was as follows: theoptimal carbon source was undiluted hydrolyzate,0.2%（w/w） urea,0.3%CaCO₃,0.3%ammonium acetate, pH6.5,37℃, and cultivated by intermittent oscillation. Under theoptimal condtion, fermented with corn cob hydrolyzate, these results were found: solventproduction was steady, butanol and total solvent yield reached9.52g/L and14.36g/L, the yieldpercentage by each gram reducing sugar reached0.14g and0.22g, respectively.