Purpose of strain selection and breeding 

1.Prevent strain degradation.

2.Solve practical production problems.

3.Improve production capacity.

4.Improve product quality.

5.Develop new products.

Selection of strains 

1.Newly isolated wild-type strains in nature are more sensitive to mutagenesis treatment and can easily achieve good results.

2. The strain obtained by production selection in production is more similar to the wild type and is also a good starting strain.

3.Each mutagenesis treatment has a certain improvement of the strain, often multiple mutagenesis can accumulate more improvement.

4.the starting strain can be selected at the same time 2 to 3 strains, after the treatment comparison, the more suitable starting strain will be left for continued mutagenesis.

5. To try to choose haploid cells, single nucleus or multicellular body with few nuclei to make the starting mutagenic cells, this is due to the fact that most of the variant traits are recessive, especially the high yield genes.

Methods for breeding industrial strains 

1.Gene mutation: natural selection, mutagenic breeding.

2.Genetic recombination: hybridization, protoplast fusion, genetic engineering.

3.Direct gene evolution: point mutation, error-prone PCR, homozygous DNA Shuffling, etc.

Factors to be considered in the selection of breeding methods

(1) The nature of the trait to be improved and the relationship to the fermentation process (e.g., batch or continuous fermentation tests).

(2) The degree of clarity of knowledge of the genetic and biochemical aspects of this particular strain.

(3) Economic cost.

If little is known about the basic traits of a particular strain and its processes, techniques such as random mutagenesis, screening and selection are mostly used.

If the genetic and biochemical aspects of the traits have been better known, then the means such as genetic recombination can be chosen for targeted breeding.