Breeding Of A Lactic Acid-producing Enterococcus And Optimization Of Its Culture Conditions

lactic acid bacteria(LAB)is a kind of facultative anaerobic microorganism that is rich in species and exists in human and animal intestine as probiotics.Lactobacillus are widely used in feed fermentation,food,medicine,experimental carrier bacteria have a wide range of applications.In daily production and application,if we want to make full use of lactic acid bacteria to exert its value in industrial production,it is particularly important to understand its biological characteristics in a comprehensive way.Therefore,It is s essential in the researth of food schtnle.At the same time,it is great value to optimize the culture conditions.This article is mainly for biological identification of lactic acid bacteria and its culture conditions are optimized,the main findings are as follows:After primary screening and secondary screening,the strain ZY807 was obtained and its physiological and biochemical characteristics such as its morphology,lactic acid qualitative and quantitative analysis,Gram staining were studied.After observing its morphological characteristics,it can be seen that the single colony of ZY807 strain is small with the diameter of 0.2?0.8mm,the colony is nearly circular,the edge is neat,the surface is smooth,moist and transparent.Staining results showed that the target strain possessed Gram staining positive features.These characteristics are in line with the biological morphology of lactic acid bacteria,the initial determination of strains isolated lactic acid bacteria.The analysis of 16S rRNA sequence of lactic acid bacteria and phylogenetic tree analysis turned out that the strain was enterococcus faecium.With single factor experiments,the effect of different PH,inoculum size,carbon source type and concentration,culture temperature,shaking speed and incubation time on the viable count of ZY807 were studied.According to Plackett-Burman experiment,three significant influencing factors of PH,carbon source concentration and inoculum size were selected from single factor.Finally,According to response surface optimization,the optimal culture condition were:beef extract 10 g/L,yeast extract 5 g/L,peptone 10 g/L,anhydrous sodium acetate 5 g/L and glucose 20.26 g/Diammonium citrate 2g/L,MgS04 0.58g/L,K2HP04 0.4g/L,MnS04 0.29g/L,Tween 80,pH 6.87,temperature 37 ?,inoculum size 3.8%,culture time 48 h,153 rmp.In this condition,shake flask fermentation was carried out.The viable count of ZY807 reached 4.21 × 109 cfu/mL,which was 3.34 times higher than that of 1.26 × 109 cfu/mL before optimization,which was close to the predicted value.