Screening And Preliminary Study Of Thermophilic Cellulolytic Microorganisms From Asparagus Old Stem Compost

Through the observation of hydrolyzed circle in CMC plate,8strains of bacteria and6strains of actinomycetes were isolated from the asparagus old stem compost. By comparing the ratio of hydrolytic circle diameter to colony diameter (D/d),6strains of highly efficient cellulolytic microorganisms were selected. After shaking flask fermentation, strain B-5and strain S-3showed higher cellulase activity. The CMCase activity and FPase activity of strain B-5were24.15U/mL and13.98U/mL respectively. For strain S-3, the CMCase activity was21.86U/mL, the FPase activity was12.32U/mLBy morphological observation and physiological-biochemical experiments, the strain B-5was identified as Bacillus subtilis. The16S rDNA gene sequence of strain S-3was amplified and sequenced. The phylogenetic results showed that the sequence of strain S-3was highly homologous to the sequence of Streptomyces sp.Carbon source and nitrogen source were considered as influencing factors for fermentation. The results indicated that cellulose-like carbon sources could induce the strains to produce cellulolytic enzyme, while sugar-like ones acted oppositely. CMCNa was the best carbon source for strain B-5, followed by wheat bran. Strain S-3tended to utilize wheat bran and asparagus old stem powder. The addition of nitrogen sources such as peptone and ammonium sulfate can stimulate cellulase production. Peptone was the best nitrogen source for strain B-5, followed by yeast extract. Inorganic nitrogen sources could be more effectively utilized by strain S-3compared to organic ones, and the best nitrogen source was ammonium sulfate.This paper investigated the influence of temperature and pH on the production of cellulolytic enzymes. The results revealed that optimal culture conditions for B-5were as follows:initial pH value of7.5of medium, cultivating temperature of40℃. Whereas the optimal initial pH value for S-3was6.5and cultivating temperature ranged among50℃~55℃ For strain S-3, the activity of CMCase and FPase reached the highest level of27.7U/mL and23.6U/mL at48th hour, and then decreased as fermentation time prolonged. The cellulase producing ability of strain S-3varied with the prolongation of time, and the CMCase and FPase activities reached the maximum values of24.8U/mL and18.2U/mL respectively on the8th day.