Study On Laboratory Evolution Of The Probiotic Lactobacillus Casei Zhang Of 3000 Generation

This study aimed to investigate the evolution of the probiotic Lactobacillus casei Zhang of three pedigrees of 3000 generation in identical environment. The changes of morphological characteristics and basic characteristics were measured. Besides, whole genome re-sequencing technique was used to investgate its genetic stability.Comparing to the reference strain, there was no change in the bacterial cell morphology of L. casei Zhang. The viable counts, total biomass and carbohydrate metabolism also remained stable. But the bacterial activity was changed. The tolerance of L. casei Zhang for pH 2.5 simulated gastric fluid rised slightly, pH 8.0 simulated intestinal fluid and bile salt remains unchanged. The auto-aggregating rate was higher than the reference strain. The analysis of genomes for 3000 generations revealed that there were 41 non-synonymous mutations of three pedigrees. And there were four mutations associated with metabolic. The information indicated that there were many mutations, but the morphological characteristics and basic characteristics were stable of Lactobacillus casei Zhang of three pedigrees of 3000 generation.This research played a positive role in establishing a rational method of subculturing and strains rejuvenation strategy; In addition, Laboratory evolution may further reveal the molecular mechanisms of evolutionary adaptation.