Variation of microorganisms means that the phenotypic characteristics of microbial offspring are very different from their parents. This difference is caused by the gene mutation of the offspring, that is, the nucleotide sequence of the genetic material DNA or RNA virus and phage has undergone stable and heritable changes.

Mutations include gene mutation or point mutation and chromosome aberration. Gene mutation is a type of mutation that changes because one or more base pairs on the DNA (RNA of RNA virus and phage) chain are replaced by another base pair. Chromosome aberration is a mutation caused by the change or damage of large segments of DNA chain. This includes insertion, deletion, replication, translocation, inversion, etc.

Mutations in microbial genes can be spontaneous or induced by artificial environment. The frequency of the former is extremely low, and the latter can greatly increase the frequency of mutation, and the genetic traits that meet the research objectives can be accelerated through directional screening.