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Bacteria
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
During aerobic respiration (electron transport), some highly toxic by-products of oxygen are produced which inhibit any organisms that are not equipped to detoxify them. Two of these by-products of metabolism, superoxide and hydrogen peroxide, can be produced when oxygen reacts with flavoprotein during oxygen respiration. Aerobic organisms contain the enzymes superoxide dismutase, which converts water and superoxide to hydrogen peroxide, and catalase, which converts hydrogen peroxide to water and oxygen; thereby detoxifying the superoxide and hydrogen peroxide. Strict (obligate) anaerobes, i.e., those that are killed or inhibited by traces of oxygen, contain neither superoxide dismutase nor catalase. Some obligate anaerobes, e.g., several species of Clostridium, produce superoxide dismutase but not catalase and can tolerate a small amount of oxygen, usually less than one percent partial pressure. Still others, e.g., Lactobacillus species, that must derive their energy from fermentation reactions are relatively insensitive to oxygen and are called aerotolerant anaerobes. Oxygen tolerant anaerobes are usually fermenters that possess superoxide dismutase but not catalase. Facultative anaerobes such as the enteric bacteria, e.g., Escherichia, Salmonella, and Shigella species, have the facility to derive energy from either aerobic respiration if oxygen is present or from fermentation in the absence of oxygen.
Biology of microbes
Published in Philip A. Geis, Cosmetic Microbiology, 2006
Some organisms are facultative anaerobes; they do not require oxygen but fare better when they have it. Aerotolerant anaerobes grow whether or not oxygen is present because they are not affected by it. Occasionally encountered, but relatively rarely in a manufacturing environment are obligate anaerobes, organisms that grow in the absence of oxygen. Although strict anaerobes are killed by any exposure to oxygen, they can be recovered from habitats that appear to be aerobic. This is especially true for organisms that associate with facultative anaerobes in communities where the facultative anaerobes serve as oxygen scavenging guilds to deplete any available O2. Table 2.5 summarizes oxygen status of certain bacteria.
Oxidative stress tolerance and antioxidant capacity of lactic acid bacteria as probiotic: a systematic review
Published in Gut Microbes, 2020
Among the above stressors, oxidative stress is of critical importance as it greatly influences viability and product quality.3 The oxygen sensitivity of probiotic LAB is a major factor limiting their viability, although LAB are regarded aerotolerant anaerobes. Anaerobic bacteria lack the capability to synthesize an active electron transport chain,4 which affects their survival in aerobic environments. High oxygen levels will lead the formation of reactive oxygen species (ROS), including the superoxide anion (O2–), hydrogen peroxide (H2O2), and the highly reactive hydroxyl radical (HO·). When accumulated, ROS cause oxidative stress, which results in damage to proteins, DNA, and lipids, and even cell death.5 Therefore, preventing oxidative stress in LAB cells by using O2-tolerant LAB strains and applying adequate production and storage techniques are important to ensure high bacterial viability during storage and in the gastrointestinal tract.2,6