| Probiotics have many probiotic effects,such as against intestinal infections,improving lactose metabolism,lowering serum cholesterol,improving the immune function,and relieving intestinal inflammation,while the health benefits conferred by probiotics are strain-specific.Lactobacillus is the most commonly used probiotic,and Lactobacillus rhamnosus is a nationally recognized probiotic that can be used in foods and it has a wide range of applications in food health and medicine.In this paper,the classification of 12 strains of L.rhamnosus was studied from three aspects:growth characteristics,metabolic characteristics and MLST analysis,providing a basis for the strain specificity study of L.rhamnosus and its application in the food fermentation industry.(1)Based on the growth curve data,the growth characteristics of 12 strains of L.rhamnosus were studied,with glucose,lactose and sucrose as the main carbon sources respectively.Using the difference analysis at specific time points,there was no significant difference in growth between the strains with glucose as the main carbon source(,P>0.05).With lactose as the main carbon source,12 strains of L.rhamnosus could be classified into 4 growth types:CRL1505;SP1;LV108;the remaining 9 strains belonged to the same growth type.With sucrose as the main carbon source,12 strains of L.rhamnosus could be classified into 5 growth types:CRL1505;grx19;LV108;LYO;the remaining 8 strains belonged to the same growth type.Using classification PCA analysis based on OD600 nm values of each strain at all 193 time points,with glucose as the main carbon source,12 strains of L.rhamnosus could be classified into 7 growth types:151m and hsryfm1301;Bm01,CRL1505,F,grx19 and LV1;the remaining 5 strains were 5 independent growth types.With lactose as the main carbon source,12 strains of L.rhamnosus could be classified into 8 growth types:Bm01,F,grx10,grx19 and LV1;the remaining 7 strains were 7 independent growth types.With sucrose as the main carbon source,12 strains of L.rhamnosus could be classified into 10 growth types:151m and hsryfm1301;BG and grx10;the remaining 8 strains were 8 independent growth types.(2)Using NMR-based metabolomics and principal component analysis,the characteristics of extracellular metabolites of 12 strains of L.rhamnosus were studied,with lactose and sucrose as the main carbon sources respectively.Overall,with lactose as the main carbon source,the extracellular metabolites of the 12 strains of L.rhamnosus strains showed typical clustering differentiation based on fermentation time 10 h and 30 h.With sucrose as the main carbon source,the extracellular metabolites of the 12 strains of L.rhamnosus strains did not show significant clustering differentiation based on fermentation time 10 h and 30 h.At 10 h and 30 h during the fermentation,the extracellular metabolites of the 12 strains of L.rhamnosus strains showed clustering differentiation based on the main carbon sources lactose and sucrose.According to the clustering analysis of the extracellular metabolites of the strains,12 strains of L rhamnosus were classified into up to 2 metabolic types.(3)Using the MLST technique to study the genetic distance between 12 strains of L.rhamnosus,and deducing the evolutionary relationship between the strains.According to the results of MLST analysis,12 strains of L.rhamnosus were classified into 7 STs.ST3 contains 4 strains:BmOl,F,grx19 and LV1;ST1 contains 2 strains:151m and hsryfm1301;ST2 contains 2 strains:BG and grx10;ST4,ST5,ST6 and ST7 contain only one strain:CRL1505,LV108,LYO and SP1,respectively.In summary,the growth characteristics analysis based on the classification PCA and the MLST based on the base difference of the housekeeping genes have strong consistency and some difference in the identification of the strain level.Meanwhile,there were some differences in making use of different carbon sources of different L.rhamnosus strains,indicating that these strains have strain specificity in carbon sources utilization. |
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