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#aerobic bacteria

3 public questions tagged with this topic.

Microbial Physiology

What is the role of superoxide dismutase in aerobic bacteria?

Superoxide radical generated when flavoenzymes and respiratory chain components univalently reduce oxygen, highly toxic inactivating dehydratases bearing exposed iron sulfur clusters like aconitase and fumarase releasing free iron that fuels Fenton chemistry producing hydroxyl radical. Superoxide dismutase constitutes primary defense dismutating two superoxides into dioxygen and hydrogen peroxide reaction two O2 superoxide plus two protons to O2 plus H2O2. Enzymes classified by metal cofactor manganese SodA inducible by SoxRS, iron SodB constitutive, copper zinc SodC periplasmic exported via Sec pathway. Periplasmic SodC crucial for pathogenic survival inside macrophages generating oxidative burst. Product H2O2 subsequently detoxified by catalase KatG KatE and alkyl hydroperoxide reductase AhpCF. Without SOD cells show auxotrophy for branched chain amino acids, elevated mutation frequency, and sensitivity to redox cycling agents paraquat. Therefore enzyme role is conversion of superoxide into oxygen and peroxide, not DNA repair nor ATP enhancement, intermediate step in reactive oxygen species detoxification cascade protecting metalloproteins and genome integrity during aerobic growth.

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Superoxide dismutase - ROS detoxification.

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Microbial Physiology

Which enzyme is crucial for breaking down hydrogen peroxide in aerobic bacteria?

Aerobic respiration inevitably leaks electrons to dioxygen generating superoxide and hydrogen peroxide. H2O2 is particularly hazardous because ferrous iron drives Fenton reaction producing hydroxyl radical that nicks DNA phosphodiester backbone, carbonylates proteins, and peroxidizes lipids. Aerobes counter with catalase, extraordinarily efficient heme tetramer with kcat approaching ten million per second, diffusion limited perfect enzyme. Active site ferriprotoporphyrin IX cycles between ferric resting state and Compound I oxoferryl radical after binding first H2O2, then reduced by second H2O2 releasing water and dioxygen net reaction 2 H2O2 to 2 H2O plus O2 without external reductant. Escherichia coli encodes KatG bifunctional hydroperoxidase I during logarithmic growth and KatE HPII induced by RpoS sigma in stationary phase. Staphylococcus aureus catalase positivity yields vigorous bubbling, diagnostic distinction from Streptococcus. Deletion mutants exhibit hypersensitivity to H2O2, defective colonization, and increased mutation rates, underscoring central role in oxidative stress defense and survival in oxic niches and host tissues.

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 6: Oxidative stress - Catalase mechanism.

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