The Characteristic Of An Efficient Microbial System With Lignocellulosic Degradation Bacteria

Lignocellulosic is main substrate in the stage of hydrolysis during process of agricultural waste's two-phase anaerobic digestion. It is difficult to be degraded due to its complex structure, which is the rate-limiting step during the whole fermentation. The research about microbial system using degradation products of lignocellulosic as direct substrate of the methane producing fermentation, has important application value on the use of lignocellulosic wastes, and lays the foundations for the realization of biogas production to industrialization.Habituated culture of existing lignocellulose degradation microbial system were conducted in this study, as a result, we obtained a group of fast degradation strains, which had significantly high degradation effect for cellulose and hemicellulose, and good degradation ability for lignin. The best dissolved oxygen amount of the microbial system during degradation process of cellulose was 0.05-0.09 mg/L, and the optimized range of pH was 6-8. During process of fermentation in batch culture, the microbial system could degrade 42.5% of medium straw after static culture at 50°C for 3 d, the overall degradation rate of rice straw after 15 d could reach 89%. The main liquid end products during fermentation was acetic acid, whose mass concentration achieved the maximum value of 2.58 g/L in the 3rd day, the end product of liquid phase at this time also reached the maximum total amount of 2.98 g/L. During the process of fed-batch fermentation culture, this microbial system showed stronger ability of lignocellulose degradation. At the end of experiment, degradation rate of straw in each medium group was 80%-85%. In addition to A₁ group, the other four groups' acetic acid contents were changing nearly in law with addition of rice straw, that is to say, the content of acetic acid achieve peak value after 24 h of straw addition, and then gradually reduced until the next addition. The acetic acid content of A₁ group was constantly stable at the level of 2 g/L in the whole fed-batch fermentation process. Therefore, A₁ group had more actual application value compared to the other four groups. The acetic acid contents in 5 groups were all less affected by extraction and addition of medium.Through analysis of structural changes of the microbial system in each group's fermentation broth during intermediate and final stage of fed-batch fermentation process using denaturing gradient gel electrophoresis (DGGE), it was found that flora structure of microbial system were quite different between the two periods. There were 19 bands of 16sRNA in DGGE patterns, their searching results in BLAST database were: Uncultured bacterium, Uncultured bacterium tbr1-10, Ureibacillus sp. A3.03, Ureibacillus sp. A3.03, Clostridium islandicum strain AK1, Ureibacillus sp. A3.03, Ureibacillus sp. A3.03, Uncultured Bacilli bacterium clone SHBZ1189, Brevibacillus borstelensis strain U404, Clostridium straminisolvens, Uncultured Bacilli bacterium clone SHBZ1189, Uncultured Bacillus sp. clone 124, Uncultured Bacillus sp. clone 26, Clostridium sp. PML14, Clostridium straminisolvens, Uncultured bacterium clone TBM.19OCT-28, Uncultured Bacilli bacterium clone SHBZ1189. Among the total, Ureibacillus sp. A3.03 was the dominant flora during the intermediate stage of fermentation, however, its amount was very low during the end stage. This case was just oppositing to that of Brevibacillus borstelensis strain U404, Uncultured bacterium gene Band10, Clostridium straminisolvens, Uncultured Bacilli bacterium clone SHBZ1189. Clostridium islandicum strain AK1 was constantly the dominant flora during the whole fed-batch fermentation process.