The purpose of microbial breeding is to artificially accumulate some metabolites of microorganisms, guide the metabolic pathway of biosynthesis to develop in the required direction, or promote intracellular gene mutation or optimize genetic traits through recombination, so as to artificially control microorganisms and obtain the high-yield, high-quality and low-consumption strains we need.

In order to achieve this goal, the following methods can be adopted:

1. Mutation breeding: This refers to treating microbial cells with various mutagens, increasing the random mutation frequency of genes, and then obtaining the required high-yield and high-quality strains through certain screening methods (or specific screening).

2. Metabolic engineering breeding: This is a kind of breeding technology that uses genetic engineering technology to precisely manipulate specific metabolic pathways in microbial metabolic network, change the original regulatory system of microorganisms, and greatly improve the activity or yield of target metabolites. According to the different metabolic characteristics of microorganisms, methods such as changing metabolic pathway, expanding metabolic pathway and constructing new metabolic pathway are generally adopted to achieve the goal.

3. In vivo gene recombination: It means that the recombination process takes place in cells, which is relative to in vitro DNA recombination technology (or genetic engineering technology). In vivo gene recombination breeding refers to the breeding method of using genetic methods and technologies such as conjugation, transformation, transduction and protoplast fusion to recombine genes in microbial cells to increase the combination of excellent characters or lead to polyploidy, so as to obtain excellent strains.