Improved ATP supply enhances acid tolerance of Candida glabrata during pyruvic acid production

摘要

Aims:A major problem in industrial fermentation of organic acids with micro-organisms is to ensure a suitable pH in the culture broth. To circumvent this problem, we investigated the effect of citrate, which is a widely used auxiliary energy co-substrate, on cell growth, organic acid production and pH homeostasis among extracellular environment, cytoplasm and vacuole, in the pyruvic acid production by Candida glabrata CCTCC M202019 under different pH conditions.Methods and Results:Analysis of intracellular ATP regeneration, cytoplasmic and vacuolar pH values under different culture conditions points towards a relief of stress when C. glabrata is exposed to lower pH, if citrate is added. When 50 mmol l-1 citrate was added to the culture medium, the intracellular ATP concentrations increased by 20 center dot 5% (pH 5 center dot 5), 20 center dot 4% (pH 5 center dot 0) and 39 center dot 3% (pH 4 center dot 5), and higher pH gradients among the culture broth, cell cytoplasm and vacuoles resulted. As a consequence, the cell growth and pyruvic acid production of C. glabrata CCTCC M202019 were significantly improved under pH 5 center dot 0 and 4 center dot 5.Conclusions:The acid tolerance of yeast can be improved by enhancing the ATP supply, which helps to maintain higher pH gradients in the system.Significance and Impact of the Study:The results presented here expand our understanding of the physiological characteristics in eukaryotic micro-organisms under low pH conditions and provide a potential route for the further improvement of organic acids production process by process optimization or metabolic engineering.