Screening And Identification Of A Strain With High Cellulase Activity And Its Straw Degradation Characteristics

Crop straw is the most abundant collulose in the world.The special structure of the collulose molecule,along with the particularity of the existence state of a majority of collulose materials(exist in the form of wood)in nature,so,the ratio of using the resourse is low now,what is more,most of it have become the source of pollution for being discarded in natural environment or being burnt.How to transform the discarded straw fibre into monosaccharide or proteins on a large scale and transform alcohol,feed even food ulteriorly has become a hotspot in worldwide study,also a effective way of resolving the short-commons,the lack of feed resource and the environmental pollution.Cellulase is the kind of enzyme including multi-component which can hydrolyze theβ-D-indican bond of cellulose to glucose.The major organism that can decompose cellulose are fungi:Trichoderma,Aspergillus,Penicillium and some bacteria in nature. But at present most studies are focused on the effect of Trichoderma,Aspergillus, Penicillium on insoluble cellulose treated by physics and chemical methods including the radiation,steam demolition,expansion,milling,acidification,alkalize and so on.Because of high cost of production and serious pollution to the environment,these methods limit the efficient utilization of crop straw.Screening the natural microbial organism with collulose degradation ability is a basic way to solve the problem above.By high though screening(HTS) technology,we obtained following result.In this research,35 bacterial strains and 11 fungal strains that have efficient cellulose degradation ability have been obtained.With natural straw as carbon source,we obtained a strain of filamentous fungi that could effectively degenerate crop straw cellulose.This strain was preliminarily identified as Gibberella fujikuroi according to morphologic taxonomy and the analysis of its 18S rDNA gene sequences.With unsettled straw as only carbon source,various factors including nitrogen source, inoculating quantities,incubating time,initial temperature,initial pH et al that can affect the production of cellulase have been studied.The results showed that the best nitrogen source was CO(NH₂)₂,inoculating volume was 5%,incubating time was 120 h,initial temperature was 28～37℃and initial pH of culture medium was 5～6. SEM analysis showed that Gibberella fujikuroi degradated the cellulose from the inner surface to the external surface.Comparison with the unsettled rice straw,the ratio of degradation of cellulose,hemicellulose and xylogen reached 38.9%,57.9%and 26.5%. The ratio of straw weightlessness reached over 53%via the fungis action on natural straw for 8 d.The analysis of its enzymatic compositions showed that Gibberella fujikuroi could product a variety of degrading enzymes,the activity of cellulose(CMCase),natural cellulase and FPAase reached 1.723 IU/mL,0.368 IU/mL and 0.344 IU/mL.The optimal conditions for the enzymatic reaction were about 50℃and pH 6;Under 50℃,at pH 5～6,the enzyme showed high activity and good stability;Mg²⁺,Ca²⁺ were the activators and Pb²⁺,Cu²⁺ were the inhibitors of the enzyme.These characterization have not being reported,so it established bases for improving the strain and increasing its enzymatic activity in order to meet application in industrial production.