Bacterial Respiration and E. coli Bioenergetics

Vocabulary flashcards related to bacterial respiration, E. coli bioenergetics, and nitric oxide resistance mechanisms.

Electron Transport Chain

The respiratory chain where NADH & FADH2 feed electrons, leading to ATP production.

Aerobic Respiration

Energetically downhill electron transfer from a donor molecule (e.g., NADH) to oxygen, reduced to water, coupled to ion translocation and electrochemical gradient generation.

Fermentation

Reduction of endogenous organic compounds to produce fermentation products (e.g., lactate, acetate), maintaining redox balance.

Anaerobic Respiration

Transfer from a donor molecule (e.g., NADH) or ion to a molecule other than oxygen or to an ionic species, coupled to ion translocation.

NADH dehydrogenases

Enzymes, such as CydABXH AppCBX and CyoABCD in E. coli, that transfer electrons from NADH.

Terminal Oxidases

Enzymes that transfer electrons to the final electron acceptor in the electron transport chain (e.g., oxygen in aerobic respiration).

Nitrate/Nitrite Reductases

Enzymes that reduce nitrate or nitrite during anaerobic respiration.

UQ-pool

Ubiquinone pool; generally used aerobically in E. coli's respiratory chain.

MQ-pool

Menaquinone pool; generally used anaerobically in E. coli's respiratory chain.

Nuo (NDH-I)

NADH dehydrogenase I; an electrogenic complex in E. coli that conserves energy through proton gradient formation. Expressed maximally in aerobic conditions.

Cytochrome bo′

A terminal oxidase; expressed under aerobic conditions with a Km (O2) of 6mM and oxidizes ubiquinol. Proton pump with H+/e- = 2.

Cytochrome bd-I

A terminal oxidase; expressed under microaerobic conditions (low O2), with Km (O2) = 270 nM and oxidizes ubiquinol. Only vectorial proton translocation: H+/e- = 1

NarGHI Nitrate Reductase

Transmembrane nitrate reductase that does not pump protons; contributes to PMF via vectorial translocation: H+/e- = 1. Expressed maximally under anaerobic conditions in the presence of nitrate.

NrfABCD Nitrite Reductases

Nitrite reductase that contributes to PMF via vectorial translocation and catalyzes the six-electron reduction of nitrite to ammonia. Expressed under anaerobic/microaerobic conditions in the presence of nitrate and nitrite.

Dissimilative Metabolism

Under anaerobic conditions where there is an excess of reduced electron carriers, E. coli can perform nitrate/nitrite dissimilation (no PMF generated)

Nitric Oxide (NO)

A respiratory inhibitor produced by the host immune system that is a toxic radical with bactericidal properties. Destroys Fe-S clusters, inhibits respiratory cytochromes, and modifies proteins.

NrfABCD's Role in NO Detoxification

Complex detoxifies NO in E. coli; NO is an intermediate during the conversion of nitrite to ammonia, acts as a protective mechanism during infection

Cytochrome bd-I's Role in NO Resistance

Confers resistance to NO in E. coli and enables respiration in the presence of NO. Expressed in high abundance in UPEC cells isolated from bladder infections, where [O2] is low and NO is present.