Cellulase Production And Enzymatic Activity Of Cellulose-degrading Fungi With Detoxification Ability

Production of ethanol using corn stover has been considered as an effectiveway to solve energy crisis. Pretreatment is required to break up lignocellulosestructure prior to bio-ethanol production, However, the by-products, inhibitingfermentation, are formed and released in this process. Therefore, removal of theseinhibitors, also termed as detoxification, is necessary. Using bacteria fordetoxification has advantages such as no additional products, low cost and safety.These bacteria is termed as detoxifying bacteria.Findings showed that during detoxification cellulose can be produced, whoseexpenses are a large part of cost in ethanol production. If cellulose produced bydetoxifying bacteria can be used, the cost will be further reduced. Therefore, in thispaper, four typical detoxifying bacteria were selected for the research of inhibitorson cellulose production and cellulose on enzymatic hydrolysis. First, to researchthe mechanism of various inhibitors working on cellulase, single and multi-factorwere carried out. Results showed that inhibitors exerted different influences oncellulase synthesized by detoxifying bacteria. When Aspergillus niger NRRL330and Aspergillus niger NRRL1956grew under acid condition with acetic acidconcentration of1g/L, the synthesis of cellulase was promoted. Additionally,when several inhibitors co-existed, synergistic inhibitory effect would be showed,compared to single inhibitors, which could promote the production of cellulaseunder low concentration. Secondly, enzymatic reactions during detoxification wasresearched, showed that Aspergillus niger NRRL330and Aspergillus nigerNRRL1956promoted enzymatic activity under low acetic acid concentration(1g/L). FPA, CMC and CB were raised by37%，24%and9%, respectively. Theeffect of inhabitation of by-products on cellulase produced by these four bacterialstrains was a common phenomenon. Among them, by comparison to acetic acid andfurfural, formic acid posed lower inhibitory effect on these strains.Hydroxymethylfurfural exerted no effect on CB during enzymatic hydrolysisinvolved three detoxifying aspergillus, with a higher level of3IU/ml for thesecellulase. Therefore, cellulase produced by detoxifying bacteria, aspergillus, canbe as an alternative to β-glucosidase. The maximum CB activities obtained undersingle factors were0.2g/L(formic acid),1g/L(furfural), and0.1g/L(hydroxymethylfurfural), respectively. These results agreed with previous reports.The effects of cellulase production were further tested so as to confirm thepreceding assumptions. During saccharification, the total glucose yields for those without β-glucosidase were92.3%，100.7%，78%and87%of those added withβ-glucosidase, respectively. Thsed findings showed that cellulase produced bydetoxifying bacteria almost completely replaced commercial β-glucosidase. On theother hand, the results mentioned above showed that saccharification could beimproved upon the removal of inhibitors, therefore, the cost could be reduced dueto the decreasing use of commercial cellulase.