Research On The Nutrients Consumption Patterns Of Streptococcus Thermophilus TF96

At present,the research on the nutritional requirements of Streptococcus thermophilus mainly focuses on the determination of the amino acid requirement of a few strains,while the information about the requirements of vitamins,purine,pyrimidine and metal ions is rarely reported.Therefore,the aim of this study is to explore the demand and consumption patterns of Streptococcus thermophilus for each nutrient,and to provide a theoretical basis for the quantitative analysis of high density medium.In this study,Streptococcus thermophilus was cultured by chemically defined medium(CDM)under the control of fermentation pH.On the basis of studying the growth kinetics,nutrients such as Lactose,amino acid,vitamins,purine,pyrimidine,inosine and minerals in the culture medium were analyzed by high performance liquid chromatography(HPLC)with the increase of the fermentation time and the consumption of the nutrient components with the biomass at different growth rates,which aims to elucidate the nutrient consumption patterns of Streptococcus thermophilus and provide theoretical support for the design of the high density medium.During the whole growth of Streptococcus thermophiles,the concentration of lactose decreased with the increase of fermentation time,by the result that the concentration of lactose increased with the increase of fermentation time and growth rate.Furthermore,the total consumption of lactose was 26.81 mmol/L,accounting for the initial amount of 91.78%.When the average growth rate μ1 was 0.04 h-1,the daily consumption of lactose was the highest in unit dry weight,but the effective utilization rate of lactose was the lowest when the average growth rate was μ1 because of the slight increase of biomass at this time.When the average growth rate of Streptococcus thermophilus increased from μ2(0.17 h-1)to μ3(0.21 h-1),the consumption of lactose decreased with the increase of growth rate,which indicated that the effective utilization rate of lactose was also higher at higher growth rate.During the whole fermentation period,the most consumed amino acids were leucine,aspartic acid,proline and valine and the consumption of these amino acids accounted for 8.89%,8.73%,8.39%and 7.77%of the total amino acid consumption.In terms of the consumption rate of amino acids,the consumption rate of arginine,histidine and methionine was the highest among these 20 kinds of amino acids and the consumption rate of these three amino acids were more than 95%,while the consumption rate of proline,serine and alanine was less than 50%in the cell growth process,which indicated that they are amino acids of low consumption amount..In addition,according to the result of the change in the consumption rate of amino acids with the bacteria growth rate,the bioavailability of 20 amino acids was the highest at μ2(0.17 h-1)or μ3(0.21h-1).Moreover,the consumption of the remaining amino acids except threonine in the unit cell dry weight was the highest at the average growth rate of μ1(0.04 h-1),which may be due to the fact that Streptococcus thermophilus had just entered the hysteresis,which was the stage of adapting to the new environment,thus Streptococcus thermophilus consumed large amounts of amino acids to prepare for entering the logarithmic growth phase.During the entire growth period of Streptococcus thermophilus,the most consumed vitamin was ascorbic acid,which accounts for 93.33%of the total consumption of all vitamins.The least consumed vitamin was cyanocobalamin(0.66 μmol/L),accounting for only 0.03%of the total consumption of vitamins.Biotin,niacin,p-aminobenzoic acid and riboflavin accounts for a larger consumption rate in all vitamins,and the consumption rate of these vitamins were greater than 75%.When the average growth rate increased from μ1(0.04 h-1)to μ3(0.21 h’1),the effective utilization of all vitamins except riboflavin and niacin increased with the increase of biomass,and when μ3 was 0.21 h-1,they had the highest bioavail ability.When μ4 was 0.05 h-1,the consumption of the other vitamins at this time was greater than that of μ3 except cyanobenzamid and p-aminobenzoic acid.It indicated that the utilization of these vitamins is also low in the lower average growth rate.This may be due to the fact that Streptococcus thermophilus cells accumulated a large number of metabolites at a stable period,thereby inhibiting the bacteria on the absorption of these vitamins.The results of studies on the consumption of purine,pyrimidine base,inosine and metal ions with the fermentation time and biomass showed that the most abundantly consumed alkaloids in the added base were uracil,the consumption rate of guanine was the highest and the consumption amount and consumption rate of adenine and xanthine were relatively low in the whole fermentation of Streptococcus thermophiles.The consumption amount of inosine is 10.10 μmol/L,accounting for 54.16%of the initial addition of inosine in the process of bacterial growth.The consumption amount of K+ in metal ions was the highest(9.30 mmol/L),the consumption rate of Ca2+ was the highest(29.53%),and the consumption amount and consumption rate of Mg2+ and PO4-3 were lower.In addition,the unit biomass consumption rate of purine,pyrimidine and metal ions was the highest at the average growth rate of μ1 and μ4,but since the biomass did not increase significantly at these two growth rates,Purine,pyrimidine and metal ions had the lowest effective utilization rate in the process.When the growth rate was μ2 or μ3,the effective utilization rate of these nutrients was the highest.Through the study of Streptococcus thermophilus on the consumption patterns of various nutrients,Streptococcus thermophilus has different needs of various nutrients in the growth process,some of the consumption of nutrients and utilization rate is high,and some of the consumption of nutrients and utilization is very low.Therefore,in order to achieve high-density culture Streptococcus thermophiles economically,we can reduce the consumption and utilization of nutrient in the design of Streptococcus thermophilus medium,and increase the consumption and utilization rate of the amount of nutrients added.