Isolation and identification of cassava residue substrate fermentation microorganisms and compound bacteria preparation

Cassava residue is a typical byproduct inacassava industry, containing a large amount of lignocellulose.However, if not treated timely, the cassava residuecanseriously pollute the ecological environment, due toits relatively slow degradationunder natural conditions. It is urgent to properly treatthe byproductsof cassava processingin time. At present, the cassava residue is mainly used in the production of animal feed, horticultural substrates, and industrial raw materials. Nevertheless, there are certain drawbacks in the processingof cassava residues underthese pathways. The lignocellulose is akey factor that affects the fermentation process of organic wastes. In recent years, most microbial studies on the fermentation of organic waste matrixes, such as vinasse and twigs, have focused on the cellulose-efficient degrading bacteria. This study aims to isolate, screen and identifythe microbial strains related to the fermentation of cassava residue from the natural fermentation process, thereby to obtain a composite microbial agent.An emphasis is put on the fermentation of composite microbial agent in the cassava residue matrix. The main results are as follows:Microorganisms were isolated during the four key periods of natural fermentation,including the initial stage (25℃), warming stage (25-40℃), high temperature stage (55-60℃), and decaying stage (25℃). A plate coating method was used to isolate microorganisms at different fermentation stages, where the 30 strains of bacteria were isolated in the initial stage, 54 strains in the warming stage, 25 strains in the high temperature stage, and 32 strains in the rotting stage. Further inoculation of isolated microorganisms onto Congo red medium can contribute to the selection of 54 strains with lignocellulose-degrading functions. 37 microorganisms closely related to cassava residue fermentation were identifiedusing the 16S rDNA and ITS sequencing of inner transcribed spacer region. The combination of Bacillus uplandis and Bacillus licheniformiswas the best fermenting bacterium, while the actinomycetes were the best fermenting bacterium. The red streptomyceteswere the most effective, where thefungi were best with Trichoderma viride. The strains were further compounded in proportion to form microbial agents.It was found that the mixture of three types of microorganisms had the best fermentation effect,wherethe residue cellulose content was reduced by 24.4%,while,the weight loss was significantly higher than that of commercial agents. These results demonstratedthat there was a certain synergy between microorganisms, and this synergy can contribute to promote the fermentation process of cassava pomace.The compound microbial agents can be recommendedduring this time to achievethe most efficient fermentation,including the Bacillus uplandis, Bacillus licheniformis, Streptomyces pallidus, and Trichoderma viride.