Effect Of PH On The Growth Of Lactobacillus Plantarum KDFR27

Lactobacillus plantarum were widely used in the production of fermented food as a leavening agent and potential probiotics. This aroused people’s extensive interests in researching probiotic properties, high-density culture, metabolic regulation and other aspects of Lactobacillus plantarum. Now, there still existed some prominent inadequacies in metabolic regulation of Lactobacillus plantarum, especially in amino acid metabolism. Although there were some synthetic mediums designed for Lactobacillus plantarum, the amino acid content of these media was very unbalanced, the concentrations of individual amino acids were higher than others, which made the consumption and utilization of the intracellular amino acids was very small when compared with the overall amino acid content, leading to the inaccurate results. Lacking of researches on amino acids consumption patterns and amino acid metabolism obstructed the more inexpensive media design and optimization of complex biological processes.Preliminary researches for this paper showed that Lactobacillus plantarum KDFR27 had strong fermentation activity under the uncontrolled pH fermentation conditions compared to the controlled pH(6.0) fermentation conditions. In order to clarify this phenomenon, we used Lactobacillus plantarum KDFR27 as the target strains which proliferated in the CDM medium. We analyzed the effect of the controlled(pH6.0) and uncontrolled fermentation pH conditions to growth kinetics, the main intracellular metabolic characteristics(intracellular pH, ATP, H~+-ATPase activity, NADH and NADPH content), acid consumption patterns and demand patterns of Lactobacillus plantarum KDFR27.As to the growth kinetics and intracellular metabolic characteristics, the final biomass under the controlled and uncontrolled pH fermentation conditions were respectively 7.65×107CFU/ml and 9.16×108CFU/ml. During the whole growth period, the intracellular pH under the uncontrolled pH condition was significantly higher than controlled pH condition, and the pH gradient was 1.35 higher than controlled pH condition. During the stationary phase the ATP concentration under the uncontrolled pH condition was higher than controlled pH condition at 36.66μmol/gdwprot, and during the lag phase and stationary phase the activity of the H~+-ATPase under the uncontrolled pH condition was respectively higher than controlled pH condition at 2.71 and 2.05μmol Pi/mgprot/hour. During stationary phase, the concentration of NADH under uncontrolled pH condition was higher than controlled pH condition at 1.77×10-3nmol/104 cells, and during the lag phase and logarithmic phase, the concentration of NADPH under uncontrolled pH condition was respectively higher at 0.57 and 1.56 ×10-3nmol/104 cells. The results above stated that uncontrolled pH condition contributed to increase the final biomass of Lactobacillus plantarum KDFR27, intracellular pH, pH gradient, the concentration of intracellular ATP during stationary phase and the activity of the H~+-ATPase during lag phase and stationary phase, as well as the concentration of intracellular NADH during stationary phase and the concentration of intracellular NADPH during lag phase and logarithmic phase.The total consumption of most amino acid under the controlled pH condition was higher than uncontrolled condition. During the four growth phases, the most consumed amino acids, under controlled pH condition, were Gly, Asp, Ala and Thr, whose consumption were more than 950μmol/gdw; while Tyr, Met, Met and Tyr were less consumed, whose consumption were ranging from 350 to 500μmol/gdw. Under uncontrolled pH condition, Glu, Gly, Glu and Ser whose consumption were all more than 1300μmol/gdw were most consumed; while Leu, Met, Lys and His were less consumed respectively whose consumption were ranging from 300 to 400μmol/gdw. This result indicated that different pH condition may significantly affect the selective consumption of Lactobacillus plantarum KDFR27 to most amino acid.When Lactobacillus plantarum KDFR27 grew under controlled and uncontrolled incubation conditions, except for Pro, the aggregate demand of amino acids under uncontrolled pH condition was higher than controlled pH condition. Especially Ala, whose aggregate de mand under uncontrolled pH condition was 8.82 times higher than controlled pH condition. This result demonstrated that Lactobacillus plantarum KDFR27 had greater aggregate demand for amino acids under uncontrolled pH incubation condition and Ala was signif icantly influenced by this condition. Except for Ala, Lactobacillus plantarum KDFR27 had greater aggregate demand for Glu, Asp and Gly which were all higher than 150μmol/gdw, under these two different incubation condition, and had less aggregate demand for Pro, Tyr and His which were ranging from 25 to 65μmol/gdw. Under controlled and uncontrolled pH conditions, the aggregate consumption of amino acids was over the aggregate demand 8 times and 4 times respectively, which showed that Lactobacillus plantarum KDFR27 had higher effective utilization ratio of amino acids under uncontrolled pH condition.