The Wide Application of Escherichia coli Fermentation in Microbiological Research

The microbial fermentation process has been manipulated by humans and is widely used in the production of various foods and other commercial products, including pharmaceuticals. Microbial fermentation can also be used to identify microorganisms for diagnostic purposes.

Several Gram-positive bacteria, including Lactobacillus, Leuconostoc, and Streptococcus, are collectively referred to as Lactic Acid Bacteria (LAB). Various strains are important in food production. In the production of yogurt and cheese, the highly acidic environment produced by lactic acid fermentation will denature the protein in milk and make it solidify. When lactic acid is the only fermentation product, the process is called homolactic fermentation; this is the case with Lactobacillus delbrueckii and Streptococcus thermophilus used in the production of yogurt. However, many bacteria exhibit isolactic fermentation, resulting in the production of lactic acid, ethanol and/or a mixture of acetic acid and CO 2 because they use the branched pentose phosphate pathway instead of the EMP pathway for glycolysis. An important isolactic acid fermentation tank is Leuconostoc mesenteroides, which is used for vegetables such as pickles and cabbage to produce kimchi and sauerkraut, respectively.

Lactic acid bacteria are also important in medicine. The low pH environment in the body inhibits the establishment and growth of pathogens in these areas. For example, the vaginal microbiota is mainly composed of lactic acid bacteria, but when these bacteria are reduced, the yeast will proliferate and cause yeast infections. In addition, lactic acid bacteria are important for maintaining the health of the gastrointestinal tract, so they are the main components of probiotics.

Another familiar fermentation process is alcohol fermentation, which produces ethanol. In the first reaction, pyruvate decarboxylase removes a carboxyl group from pyruvate, releasing CO 2 gas, and at the same time producing two-carbon molecule acetaldehyde. The second reaction is catalyzed by alcohol dehydrogenase, which transfers electrons from NADH to acetaldehyde to produce ethanol and NAD. The pyruvate ethanol fermentation of Saccharomyces cerevisiae is used to produce alcoholic beverages, which also increases the production of bread products due to CO 2. Outside the food industry, ethanol fermentation of plant products is important in biofuel production.

In addition to lactic acid fermentation and alcohol fermentation, there are many other fermentation methods in prokaryotes, all of which are to ensure sufficient supply of NAD + for glycolysis. Without these pathways, glycolysis would not occur, and ATP would not be obtained from the breakdown of glucose. It should be noted that, with the exception of homolactic fermentation, most forms of fermentation will produce gas, usually CO 2 and/or hydrogen. Many of these different types of fermentation pathways are also used in food production, each of which produces a different organic acid, thereby forming the unique flavor of a particular fermented food. The propionic acid produced during the fermentation of propionic acid, for example, contributes to the unique flavor of Swiss cheese.

Several fermented products have important commercial value outside the food industry. For example, chemical solvents such as acetone and butanol are produced during the acetone-butanol-ethanol fermentation process. Complex organic pharmaceutical compounds used in antibiotics (such as penicillin), vaccines, and vitamins are produced by mixed acid fermentation. Fermented products are used in laboratories to distinguish various bacteria for diagnosis. For example, intestinal bacteria are known for their ability to perform mixed acid fermentation and lower pH, which can be detected using pH indicators. Similarly, acetoin produced by bacteria during butanediol fermentation can also be detected. The gas produced by the fermentation can also be seen in the inverted Durham tube, which captures the gas produced in the broth culture.

Microorganisms can also be distinguished based on the substrates they can ferment. For example, E. coli,/a> can ferment lactose to form gas, while some of its gram-negative relatives cannot. The ability to ferment the sugar alcohol sorbitol is used to identify the pathogenic enterohaemorrhagic O157:H7 strain of E. coli, because it cannot ferment sorbitol, unlike other E. coli strains. Finally, mannitol fermentation distinguishes mannitol-fermented Staphylococcus aureus from other non-mannitol-fermented Staphylococcus.