Mechanism Of The Effect Of Temperature On The Growth Characteristics Of Lacticaseibacillus Paracasei During High-density Culture

Research on the preparation of highly active probiotic powder is of great significance for modern food development.High-density fermentation of lactic acid bacteria is the core technology for the preparation of highly active probiotic powder,and the fermentation temperature has an important influence on high-density fermentation.In this experiment,a strain of Lacticaseibacillus paracasei PC-01 with excellent probiotic properties isolated from sour yak milk in Longren Township,Dangxiong County,Lhasa,Tibet,was subjected to high-density fermentation at 32.5°C and 37.0°C.The cell phenotypic and genotypic changes at different times were observed by combining flow cytometry,transcriptome sequencing and genome sequencing techniques,and the results were as follows:(1)Phenotypic analysis showed that Lacticaseibacillus paracasei PC-01 showed a 25.9%increase in viability at the end of fermentation at 32.5°C compared to 37.0°C.The strain also showed higher esterase activity and membrane permeability,better membrane fluidity and more stable intracellular p H,indicating that the strain had better growth characteristics at32.5°C.(2)Transcriptome analysis at 37.0°C as control and 32.5°C as experimental group showed that 124,194,638 and 841 genes were significantly differentially expressed between the two groups of isolates in the late,pre-log,mid-log and end of fermentation periods,respectively.The KEGG enrichment analysis showed that the differentially expressed genes were mainly enriched in the carbohydrate metabolism,oxidative phosphorylation and amino acid metabolism pathways,indicating that the fermentation at 32.5°C resulted in enhanced carbohydrate metabolism,increased sugar consumption,stable intracellular p H and increased membrane fluidity,further elucidating the effect of temperature on the growth characteristics of Lacticaseibacillus paracasei PC-01 during high density culture.The effect of temperature on the growth characteristics of Lacticaseibacillus paracasei PC-01 in high density culture was further elucidated.(3)The results of the genomic analysis based on colony level showed that there were small differences in the average number of genes,size and GC content of the different colonies obtained from fermentation at 32.5°C and 37.0°C.In addition,analysis based on high frequency mutations yielded a higher proportion of mutations in the ppa and hfl X genes during fermentation at 32.5°C and a higher proportion of mutations in the pgd A gene during fermentation at 37.0°C,suggesting that there are also some differences at the genomic level that may have an impact on the growth of the strains.In summary,phenotypic,transcriptomic and genomic analyses revealed that Lacticaseibacillus paracasei PC-01 showed increased viability and enhanced carbohydrate metabolism,oxidative phosphorylation pathways and membrane metabolism during fermentation at 32.5°C compared to 37.0°C,which was more favourable for the growth and metabolism of the strain.The results indicate that temperature has an influence on the growth characteristics of Lacticaseibacillus paracasei PC-01 in high density culture,and this result also provides a theoretical basis and data support for the subsequent study of Lacticaseibacillus paracasei.