ABSTRACT
Lactobacillus casei Zhang is a widely recognized probiotic bacterium, which is being commercially used in China. To study the gene expression dynamics of L. casei Zhang during fermentation in soymilk, a whole genome microarray was used to screen for differentially expressed genes when grown to the lag phase, the late logarithmic phase, and the stationary phase. Comparisons of different transcripts next to each other revealed 162 and 63 significantly induced genes in the late logarithmic phase and stationary phase, of which the expression was at least threefold up-regulated and down-regulated, respectively. Approximately 38.4% of the up-regulated genes were associated with amino acid transport and metabolism notably for histidine and lysine biosynthesis, followed by genes/gene clusters involved in carbohydrate transport and metabolism, lipid transport and metabolism, and inorganic ion transport and metabolism. The analysis results suggest a complex stimulatory effect of soymilk-based ecosystem on the L. casei Zhang growth. On the other hand, it provides the very first insight into the molecular mechanism of L. casei strain for how it will adapt to the protein-rich environment.
Subject(s)
Fermentation , Lacticaseibacillus casei/genetics , Probiotics/metabolism , Soy Milk , Amino Acids/metabolism , Animals , Carbon/metabolism , China , Gene Expression Profiling , Gene Expression Regulation, Bacterial , Ion Transport/genetics , Lacticaseibacillus casei/growth & development , Lacticaseibacillus casei/metabolism , Lipid Metabolism/geneticsABSTRACT
A total of 87 yeast strains were isolated from 28 home-made koumiss samples, a traditional fermented mare milk product in Xinjiang of China. The isolates were identified by standard physiological and biochemical tests and analysis of the large-subunit (26S) rDNA gene D1/D2 domain sequences. They are proved to be Saccharomyces unisporus (48.3% of the isolates), Kluyveromyces marxianus (27.6%) and Pichia membranaefaciens (15.0%), Saccharomyces cerevisiae (9.2%). Among them, six isolates and a standard yeast strain were selected for analysis of D1/D2 domain sequences. They are indicated as S. unisporus, K. marxianus, S. cerevisiae, P. membranifaciens, P. fermentans, P. galeiformis and the standard yeast strain is indicated as K. lactis (100%). The results obtained demonstrate the value of using analysis of D1/D2 domain sequences methods, in conjunction with the traditional taxonomic methods based on phenotypic characteristics. This study forms an essential step towards the preservation and exploitation of the hidden oenological potential of the wealth of yeast biodiversity of the koumiss in Xinjiang Province. The result obtained shown that S. unisporus and K. marxianus were the predominant strains of koumiss in Xingjiang of China.