Effects Of Acetic Acid On The Growth And Fermentation Of Acetobacter Pasteurianus AC2005

Acetic acid is not only the material of medicine production but also the main ingredient of vinegar. Although acetic acid is toxic to microorganisms, acetic acid bacteria are commonly used in the production of vinegar, with a strong ability to oxidize ethanol and to tolerate to acetic acid. Compared to other microorganisms, acetic acid bacteria have special mechanisms of acetic acid tolerance. This paper mainly researches the effects of acetic acid on the growth, metabolism, protein expression and acetate fermentation of Acetobacter pasteurianus AC2005, which indicates the mechanisms of acetic acid tolerance.The effects of acetic acid on the growth of Acetobacter pasteurianus AC2005 reveal that low concentration of acetic acid could firstly promote and later inhibit bacteria growth. Specifically, when the concentration is 0.5%, the growth of bacteria and the comsuption of of glucose accelerate, in the meantime, the final biomass doubled than it without acetic acid. Moreover, by adding 0.5% acetic acid in culture medium, the final concentration of aceti acid increases by 14.9%, which means it improves the density of fermentation.Meanwhile, under the two conditions (with and without acetic acid), the surface morphology, cell viability, ATP content changes and changes in ADH and ALDH activity were discussed to study the effects of acetic acid on bacteria growth. The results suggest, without acetic acid, the cell is 6μm-10μm long and 3μm-5μm wide in average, with smooth surface. When it comes to add 1% acetic acid in the medium, the cell becomes 3μm-6μm long and remains the same width, with rough and small surface. Furthermore, MTT assay shows that after adding 0.5% acetic acid in the medium, the cell relative activity, intracellular ATP levels, alcohol dehydrogenase (ADH) activity and aldehyde dehydrogenase (ALDH) activity sharply increase by 150%,168%,200% and 225%, respectively. As a result, aceti acid bacteria might tolerate acetic acid by changing cell morphology, intracellular metabolism activity, ADH activity and ALDH activity.Moreover, in the state of the fermentation process, the acetic acid tolerance of A. pasteurianus AC2005 significantly improved, according to the sharp decrease of lag phase time, the maintance of cellular surface morphology and the augment of ADH and ALDH activity.Additionally, the protein expression in two different growth conditions (adding 1% acetic acid in growth medium and adding 1% acetic acid and 3.5% ethanol in fermentation medium) is detected by using LC-MS/MS and bioinformatics methods. Regarding the condition for adding 1% acetic acid, the expressions of glucose metabolism-related and TCA cycle-related proteins significantly upregulate, which partly results to the incease of cell concentration. What is more, ADH and ALDH activity increase acoordingly, but proteins associated to redox processes and amino acid synthesis significantly reduced. In contrast, under the circumstance of 1% acetic acid and 3.5% ethanol, ADH and ALDH activity and membrane-associated proteins expressions are significantly upregulated, but proteins related to glucose metabolism and TCA cycle plunge. Therefore, these results susgest that acetic acid affects the process of glucose metabolism and TCA cycle processes, and ethanol inhibits both the two processes, as well as increase the acetic acid tolerance by influencing the ADH and ALDH activity and membrane-associated proteins to oxidize the alcohol.