Construction And Effectiveness Of A High Efficient Microbial System For Rice Straw Degradation

With the rapid development of agriculture,large quantities of straws are produced as agricultural by-products,the number is up to 900 million tons,of which rice straw is about200 million tons.By constructing the microbial community and using microorganisms to degrade straw can not only facilitates the return of straw to the field,but also realizes the utilization of straw as a resource.It is of great significance to environmental protection and the recycling of biomass resources.The microbial community from different sources was combined,then the combination with the best straw degradation effect was selected and named as LCW.Using rice straw as a carbon source to restrict culture of LCW until the microbial community reaches stable state and then conduct a single factor test.On the basis of the single factor experiment,the three factors of temperature,peptone concentration and calcium carbonate concentration were selected to optimize the degradation conditions by response surface method,and a ternary quadratic regression mathematical model was established for the degradation rate of rice straw.The optimal degradation conditions were 56 ℃,peptone concentration 4.8 g/L and calcium carbonate concentration 3.9 g/L.The straw degradation rate reached 64.7±1.1% after10 d of incubation at constant temperature.Metagenomics was used to analyze the difference in degradation of rice straw and corn stalks by the microbial community at different temperatures.The results showed that the species structure of the microbial community had changed at the phylum,genus,and species level,and the symbiotic bacteria and non-cultivable bacteria became the dominant bacteria genus at 56°C degradation conditions.There is not much difference in the functional metabolism of the microbial community.KEGG analysis shows that the abundance of quorum sensing and two-component regulation systems has increased.The changes in the physical and chemical properties of the straw during the degradation process were measured,under the condition of 56℃,the degradation rate of rice straw and corn stalk by the composite flora after 15 days of degradation was 65.1±2.4% and 55.2±2.3%,respectively.FTIR analysis shows that multiple characteristic peaks related to straw degradation have alter.The p H value of the fermented liquid alter from neutral to alkaline during the degradation process.The small molecule acid is mainly acetic acid during the fermentation process,but it is subsequently consumed by microorganisms.With the method of transparent circle and enzyme activity determination,16 strains of cellulose-degrading bacteria were screened from LCW,of which 3 strains had the ability to efficiently degrade cellulose and hemicellulose.Molecular technical identification showed that these 3 strains were A1(Bacillus subtilis),A14(Bacillus velezensis)and A18(Aneurinibacillus thermoaerophilus).Adding A14 to LCW for mixed culture can increase the ability of LCW to degrade rice straw by 9.65±1.2%.