Abstract
BackgroundAcetic acid bacteria (AAB) are widely applied in food, bioengineering and medicine fields. However, the acid stress at low pH conditions limits acetic acid fermentation efficiency and high concentration of vinegar production with AAB. Therefore, how to enhance resistance ability of the AAB remains as the major challenge. Amino acids play an important role in cell growth and cell survival under severe environment. However, until now the effects of amino acids on acetic fermentation and acid stress resistance of AAB have not been fully studied.ResultsIn the present work the effects of amino acids on metabolism and acid stress resistance of Acetobacter pasteurianus were investigated. Cell growth, culturable cell counts, acetic acid production, acetic acid production rate and specific production rate of acetic acid of A. pasteurianus revealed an increase of 1.04, 5.43, 1.45, 3.30 and 0.79-folds by adding aspartic acid (Asp), and cell growth, culturable cell counts, acetic acid production and acetic acid production rate revealed an increase of 0.51, 0.72, 0.60 and 0.94-folds by adding glutamate (Glu), respectively. For a fully understanding of the biological mechanism, proteomic technology was carried out. The results showed that the strengthening mechanism mainly came from the following four aspects: (1) Enhancing the generation of pentose phosphates and NADPH for the synthesis of nucleic acid, fatty acids and glutathione (GSH) throughout pentose phosphate pathway. And GSH could protect bacteria from low pH, halide, oxidative stress and osmotic stress by maintaining the viability of cells through intracellular redox equilibrium; (2) Reinforcing deamination of amino acids to increase intracellular ammonia concentration to maintain stability of intracellular pH; (3) Enhancing nucleic acid synthesis and reparation of impaired DNA caused by acid stress damage; (4) Promoting unsaturated fatty acids synthesis and lipid transport, which resulted in the improvement of cytomembrane fluidity, stability and integrity.ConclusionsThe present work is the study to show the effectiveness of Asp and Glu on metabolism and acid stress resistance of A. pasteurianus as well as their working mechanism. The research results will be helpful for development of nutrient salts, the optimization and regulation of high concentration of cider vinegar production process.
Highlights
Acetic acid bacteria (AAB) are widely applied in food, bioengineering and medicine fields
The research results will be helpful for development of nutrient salts, the optimization and regulation of high concentration of cider vinegar production process
Determination of key growth factor Among 16 types of amino acids, it was found that only aspartic acid (Asp), Glu and Pro could enhance the cell growth significantly
Summary
Acetic acid bacteria (AAB) are widely applied in food, bioengineering and medicine fields. The setoxic effects are related to the weak lipophilic nature of the undissociated acid that enables the molecule to cross the cytoplasmic membrane This diffusion is generally thought to dissipate ion gradients, increase the internal acetic acid concentration, and/or disrupt membrane processes, thereby poisoning the cell [5, 8, 9]. The cytotoxicity of acetic acid on its microbial producer has become a rate-limiting issue in efforts to further improve the fermentation efficiency of this important natural product and has been the subject of much study. There is an urgent need for a new method which is simple and easy to implement in industry to improve the acid resistance of AAB, promoting acetic acid fermentation efficiency and high concentration of vinegar production
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