Vinegar Fermentation
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Cited by 3 publications
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Acetic acid bacteria (AAB) have, for centuries, been important microorganisms in the production of fermented foods and beverages such as vinegar, kombucha, (water) kefir, and lambic beer. Their unique form of metabolism, known as “oxidative” fermentation, mediates the transformation of a variety of substrates into products, which are of importance in the food and beverage industry and beyond; the most well‐known of which is the oxidation of ethanol into acetic acid. Here, a comprehensive review of the physiology of AAB is presented, with particular emphasis on their importance in the production of vinegar and fermented beverages. In addition, particular reference is addressed toward Gluconobacter oxydans due to its biotechnological applications, such as its role in vitamin C production. The production of vinegar and fermented beverages in which AAB play an important role is discussed, followed by an examination of the literature relating to the health benefits associated with consumption of these products. AAB hold great promise for future exploitation, both due to increased consumer demand for traditional fermented beverages such as kombucha, and for the development of new types of products. Further studies on the health benefits related to the consumption of these fermented products and guidelines on assessing the safety of AAB for use as microbial food cultures (starter cultures) are, however, necessary in order to take full advantage of this important group of microorganisms.
Acetic acid bacteria (AAB) have, for centuries, been important microorganisms in the production of fermented foods and beverages such as vinegar, kombucha, (water) kefir, and lambic beer. Their unique form of metabolism, known as “oxidative” fermentation, mediates the transformation of a variety of substrates into products, which are of importance in the food and beverage industry and beyond; the most well‐known of which is the oxidation of ethanol into acetic acid. Here, a comprehensive review of the physiology of AAB is presented, with particular emphasis on their importance in the production of vinegar and fermented beverages. In addition, particular reference is addressed toward Gluconobacter oxydans due to its biotechnological applications, such as its role in vitamin C production. The production of vinegar and fermented beverages in which AAB play an important role is discussed, followed by an examination of the literature relating to the health benefits associated with consumption of these products. AAB hold great promise for future exploitation, both due to increased consumer demand for traditional fermented beverages such as kombucha, and for the development of new types of products. Further studies on the health benefits related to the consumption of these fermented products and guidelines on assessing the safety of AAB for use as microbial food cultures (starter cultures) are, however, necessary in order to take full advantage of this important group of microorganisms.
Mycofactocin (MFT) belongs to the class of ribosomally synthesized and posttranslationally modified peptides conserved in many Actinobacteria. Mycobacterium tuberculosis assimilates cholesterol during chronic infection, and its in vitro growth in the presence of cholesterol requires most of the MFT biosynthesis genes (mftA, mftB, mftC, mftD, mftE, and mftF), although the reasons for this requirement remain unclear. To identify the function of MFT, we characterized MFT biosynthesis mutants constructed in Mycobacterium smegmatis, M. marinum, and M. tuberculosis. We found that the growth deficit of mft deletion mutants in medium containing cholesterol—a phenotypic basis for gene essentiality prediction—depends on ethanol, a solvent used to solubilize cholesterol. Furthermore, functionality of MFT was strictly required for growth of free-living mycobacteria in ethanol and other primary alcohols. Among other genes encoding predicted MFT-associated dehydrogenases, MSMEG_6242 was indispensable for M. smegmatis ethanol assimilation, suggesting that it is a candidate catalytic interactor with MFT. Despite being a poor growth substrate, ethanol treatment resulted in a reductive cellular state with NADH accumulation in M. tuberculosis. During ethanol treatment, mftC mutant expressed the transcriptional signatures that are characteristic of respirational dysfunction and a redox-imbalanced cellular state. Counterintuitively, there were no differences in cellular bioenergetics and redox parameters in mftC mutant cells treated with ethanol. Therefore, further understanding of the function of MFT in ethanol metabolism is required to identify the cause of growth retardation of MFT mutants in cholesterol. Nevertheless, our results establish the physiological role of MFT and also provide new insights into the specific functions of MFT homologs in other actinobacterial systems. IMPORTANCE Tuberculosis is caused by Mycobacterium tuberculosis, and the increasing emergence of multidrug-resistant strains renders current treatment options ineffective. Although new antimycobacterial drugs are urgently required, their successful development often relies on complete understanding of the metabolic pathways—e.g., cholesterol assimilation—that are critical for persistence and for pathogenesis of M. tuberculosis. In this regard, mycofactocin (MFT) function appears to be important because its biosynthesis genes are predicted to be essential for M. tuberculosis in vitro growth in cholesterol. In determining the metabolic basis of this genetic requirement, our results unexpectedly revealed the essential function of MFT in ethanol metabolism. The metabolic dysfunction thereof was found to affect the mycobacterial growth in cholesterol which is solubilized by ethanol. This knowledge is fundamental in recognizing the bona fide function of MFT, which likely resembles the pyrroloquinoline quinone-dependent ethanol oxidation in acetic acid bacteria exploited for industrial production of vinegar.
Acetate production from corn stover hydrolysate using recombinant Escherichia coli BL21 (DE3) with an EP-bifido pathway
Background Acetate is an important chemical feedstock widely applied in the food, chemical and textile industries. It is now mainly produced from petrochemical materials through chemical processes. Conversion of lignocellulose biomass to acetate by biotechnological pathways is both environmentally beneficial and cost-effective. However, acetate production from carbohydrate in lignocellulose hydrolysate via glycolytic pathways involving pyruvate decarboxylation often suffers from the carbon loss and results in low acetate yield. Results Escherichia coli BL21 (DE3) was confirmed to have high tolerance to acetate in this work. Thus, it was selected from seven laboratory E. coli strains for acetate production from lignocellulose hydrolysate. The byproduct-producing genes frdA , ldhA , and adhE in E. coli BL21 (DE3) were firstly knocked out to decrease the generation of succinate, lactate, and ethanol. Then, the genes pfkA and edd were also deleted and bifunctional phosphoketolase and fructose-1,6-bisphosphatase were overexpressed to construct an EP-bifido pathway in E. coli BL21 (DE3) to increase the generation of acetate from glucose. The obtained strain E. coli 5K/pFF can produce 22.89 g/L acetate from 37.5 g/L glucose with a yield of 0.61 g/g glucose. Finally, the ptsG gene in E. coli 5K/pFF was also deleted to make the engineered strain E. coli 6K/pFF to simultaneously utilize glucose and xylose in lignocellulosic hydrolysates. E. coli 6K/pFF can produce 20.09 g/L acetate from corn stover hydrolysate with a yield of 0.52 g/g sugar. Conclusion The results presented here provide a promising alternative for acetate production with low cost substrate. Besides acetate production, other biotechnological processes might also be developed for other acetyl-CoA derivatives production with lignocellulose hydrolysate through further metabolic engineering of E. coli 6K/pFF. Supplementary Information The online version contains supplementary material available at 10.1186/s12934-024-02575-y.
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