Isolation And Identification Of Rice Straw-Biodegrading Actinomycetes And Its Degradation Mechanism

The rice straw resources are very abundant in China. Its degradation and transformation into feed, energy and chemical raw materials by microorganisms has great realistic meaning of the solution to environmental pollution and energy crisis.A streptomycete strain C-5 which producing high cellulase activities was selected by screening plate stained with congo red, determination of cellulase activities in liquid culture, determination of rice straw weight loss rate, detection of xylanase and ligninase activity from 27 soil samples which collected from three major rice-producing areas in Hei longjiang province. And it has great potential on the degradation of rice straw. This strain has multi-lignocellulase activities simultaneously. By studying the morphology, cultural characteristics, physiological and biochemical propertices, 16S rDNA and phylogenetic tree, strain C-5 was identified as Streptomyces griseorubens.Degradation rates of the main components of rice straw and the continuous variation of cellulase activities and xylanase activities were determined during the rice straw fermentation by S. griseorubens C-5. The cell wall composition of rice straw was degradated effectively and the content of crude fiber was obviously reduced after cultivation. The results showed that the cellulase and xylanase activities could still maintain relative higher level in most of the fermentation time.Fourier transform infrared spectroscopy (FTIR) was used to study the biodegradation process of rice straw. The analysis on the FTIR of rice straw showed that the carbohydrates, lignin and silica were degraded effectively after fermentation. Some of carbonate, silicate and polysaccharide were generated. Carboxyl group in the form of carboxylate in the process of degradation. Some inorganic cations were formed carbonate.The biodegradation process of rice straw lignin by S. griseorubens C-5 was investigated by FTIR. The results demonstrated that the main function in rice straw lignin biodegradation by S. griseorubens C-5 was oxidation which occurred on side-chain Cαoxidation of lignin monomer and the oxidative cleavage of Cα-Cβbond. Aliphatic ether bond was breaking and some short chain aliphatic hydrocarbons were degraded. The methoxyl content was significantly increased and some hydroquinone substances was formed. The degradation degree of the guaiacyl type lignin was higher than the syringic type lignin by S. riseorubens C-5.Histological changes of rice straw were observed by scanning electron microscope during fermentation by S. griseorubens C-5. The results showed that in the initial stage of biodegradation, hypha invaded in the rice straw through the end of the rice straw and were already fixed on the parenchyma of rice stem. The parenchyma of rice stem began to degrade and the wax-silicide layer was thinner significantly at the early stage of degradation. The vascular bundles and sclerenchyma began to degrade after the numerous actinomycetes colonized. The rice fragments had lost their intact structures and the parenchyma had completely disappeared and the cuticle wax and silica layer was destroyed partially after fermentation. The remaining tissues in rice stem was the part epidermal tissue which was lignified in high degree.Different culture conditions on production of cellulase of S. griseorubens C-5 were investigated. The results showed that the carbon concentration, nitrogen concentration, pH and incubation temperature were significant on the activity of CMCase. Carbon concentration was the key factor which affecting CMCase activity. The higher concentrations of carbon sources was more favorable to the synthesis of cellulose. Organic nitrogen soybean could promote the synthesis of cellulase production. The lower concentrations of nitrogen could enhance the cellulose synthesis than the higher concentrations of nitrogen. 31℃and pH 7.5 was the optimal temperature and pH of cellulose synthesis. The optimal time of the cellulase production of S. griseorubens C-5 was between 4~14 fermentation days in the optimal cellulase production condition.