Study On Mechanisms Of Probioitc Lactobacillus Casei Zhang Growing Bovine Milk And Soymilk Based On Transcriptomics And Proteomics

Lactobacillus casei Zhang is a well-recognized probiotic, which was isolated from traditional fermented milk products in Inner Mongolia area, it showed strong tolerance to acid and bile salt in vitro and antibacterial, antioixdantive and immune-regulatory effects in vivo, suggesting that it was an ideal strain for probiotic research.Milk material is a kind of favorable carrier for probiotic, which has generally recognized by researchers and the market in the world. Results revealed that growing speed of L. casei Zhang was significantly higher in soy milk than bovine milk under the same inoculum (1×107CFU/mL). What is more, the fermentation time (to pH4.5) required was respectively14.5h and18h. At the end of fermentation, the living number of L. casei Zhang in soy milk (109.10±0.08CFU/mL) was Significantly higher than bovine milk (108.24±0.09CFU/mL), suggesting that growing of L. casei Zhang was better in soy milk than bovine milk. Perhaps, it is more suitable for soy milk to product probiotic fermented products than bovine milk.According to complete genomic sequences of L. casei Zhang, growing mechanisms of L. casei Zhang in soy milk and bovine milk were analyzed from transcriptomics and proteomics through microarray biochip,2-dimensional gel electrophoresis and mass spectrum technique.Result from transcriptomic analysis showed that the expressions of84genes in stationary phase (pH4.5) were significantly higher than these in exponential phase (pH5.2) during bovine milk fermentation. Among these, the expressions of59genes were significantly upregulated (P＜0.05) and40.5%of upregulated genes was associated with carbohydrate and energy metabolism.During soy milk fermentation, in comparison with exponential phase (pH5.2),162genes in lag phase (pH6.4) and63genes in stationary phase (pH4.5) were significantly expressed (P＜0.05). Furthermore,48.6%of upregulated genes (93genes) in exponential phase was associated with amino acid transport and metabolism while48.8%significantly regulated genes (46genes) in stationary phase was associated with amino acid transport and metabolism.Result from proteomic analysis showed that a total of144protein spots were differently expressed including34spots in lag phase (pH6.4),64spots in exponential phase (pH5.2) and46spots in stationary phase (pH4.5) during growing of L. casei Zhang in soy milk compared to bovine milk. Furthermore,2-fold upregulated expression spots in three phases were respectively24,34and33. Most upregulated proteins related genes were associated with nucleotide and amino acids transport and metabolism.Further analysis revealed that when L. casei Zhang is growing in bovine milk, the key upregulated genes were associated with PTC system and Pentose Phosphate Pathway; while in soy milk, associated with protein hydrolysis enzyme system (PrtP, Opp and Pep), amino acids (gln, lys and met) and nucleotide (Pur and Pyr), especilly the active expression of protein hydrolysis enzyme system. It makes that L. casei Zhang can decompose soybean protein and provide adequate amino acids and nucleotide for itself, which is the main explanation for well-growing L. casei Zhang in soy milk.This study revealed the mechanisms of growing and metabolism of L. casei Zhang in bovine milk and soy milk at genetic level, and pointed out that growing differences were main due to different protein hydrolysis and amino acids metabolism within bovine and soy milk system.