Cellulose accounts for about 1/2 of the total dry weight of plants. It is the oldest and most abundant natural polymer material on earth, and it is the inexhaustible and most precious natural renewable resource for mankind. However, due to the high degree of polymerization of plant fiber and the high crystallinity of its molecular structure, the resource of cellulose has not been fully utilized. Among higher animals, ruminants can use cellulose with the help of rumen microorganisms, but other animals can hardly digest and use cellulose directly.
1. Source of cellulasernMicroorganisms that can secrete cellulase are the main source of cellulase, mainly fungi, bacteria, actinomycetes and some protozoa. Fungi of the genus Trichoderma, Aspergillus, Penicillium, and Acremonium can produce three types of cellulase and have a strong ability to degrade cellulose.
2. Molecular structure of cellulasernAs early as 1986, H. Van Tilbeurgh et al. used papain to restrict the CBH I molecule of Trichoderma reesei (Trichoderma reesei, also translated as Trichoderma reesei), and obtained 2 domains with independent activity: Catalytic domain (CD) with catalytic function and cellulose binding domain (CBD) with cellulose binding function. As the catalytic activity center of cellulase, CD specifically recognizes the substrates of endonuclease and exonuclease; CBD performs the role of regulating the specific activity of the enzyme on soluble and insoluble substrates, and is not necessary for the catalytic activity of the enzyme. CBD and CD are connected by a highly glycosylated link bridge. The link bridge can keep the distance between CD and CBD, which helps to form relatively stable aggregates between different enzyme molecules.
3. The nutritional mechanism of cellulasernCellulase has the following effects in improving animal nutrition:rn1) Destroy plant cell walls, so that nutrients can be fully absorbed. The cellulase, hemicellulase and pectinase are made into a composite enzyme agent, which synergistically destroys the plant cell wall, so that the nutrients in the cell are dissolved, and then further degraded by amylase and protease, which can improve the absorption rate of nutrients.
2) Supplement the deficiency of animal endogenous enzymes. Although there are some microorganisms that can secrete cellulase in the rumen of ruminants, the amount of cellulase produced is limited, which makes the digestion and utilization of cellulose not high. Monogastric animals lack endogenous
cellulase in their stomachs and cannot digest and utilize cellulose. The addition of cellulase can not only help animals digest and utilize cellulose, but also improve the intestinal environment.
3) Reduce or eliminate feed anti-nutritional factors. Macromolecular substances such as cellulose, hemicellulose, and pectin are partially dissolved in water to produce viscosity. This viscosity is a barrier to endogenous enzymes, which prevents the degradation of cellulase and reduces the amount of nutrients. Absorption, after supplementing cellulase, the viscosity decreases, the diffusion of endogenous enzymes and the contact with nutrients increase, so that the feed can be fully digested and absorbed.
4. Application of cellulase in animal husbandry production
4. 1 Application of cellulase in ruminant productionrnAs a new type of feed additive, cellulase has become a research hotspot in animal feed production. The addition of exogenous cellulase to ruminant feed can synergize with the endogenous enzymes produced by rumen microorganisms such as hemicellulase, pectinase and glucanase to improve the internal environment of the rumen.
4. 2 Application of cellulase in pig and poultry productionrnIn the production of pigs, poultry and other animals, cellulase preparations have been widely used. The gastric juice of pigs, poultry and other animals lacks enzymes for digesting crude fiber. However, in recent years, it has been proved that feeding a certain amount of crude fiber can improve the digestion, physiology, reproduction, and carcass quality of animals. Adding a small amount of crude fiber to the diet can promote gastrointestinal peristalsis, stimulate the secretion of gastrointestinal digestive enzymes, and improve the digestibility of animals. However, animals such as pigs and poultry cannot digest and absorb crude fiber well. Therefore, if cellulase is added to the diet to help them digest crude fiber feed, the feed conversion rate can be improved.
ãrn4. 3 Application of cellulase in the production of Chinese veterinary drugsrnMore than 90% of Chinese veterinary medicines are botanicals. The main component of botanical cell walls is cellulose. Cellulase can destroy the cell walls of botanicals and promote the dissolution of active ingredients in botanicals, thereby enhancing the efficacy of botanicals.
At present, the production of
enzymes generally has problems such as small scale, backward technology, low enzyme activity of bacterial strains, and high production costs. With the rapid development of various interdisciplinary subjects such as biochemistry, molecular biology, bioinformatics and genetic engineering, people's basic research work on cellulase has gradually deepened. It is hoped that through the screening of high-efficiency cellulose-degrading bacteria from nature, genetic engineering methods are used to construct "engineered bacteria" with high activity and large enzyme production.