How Escherichia coli Tolerates Profuse Hydrogen Peroxide Formation by a Catabolic Pathway

Abstract

When Escherichia coli grows on conventional substrates, it continuously generates 10 to 15 M/s intracellular H 2 O 2 through the accidental autoxidation of redox enzymes. Dosimetric analyses indicate that scavenging enzymes barely keep this H 2 O 2 below toxic levels. Therefore, it seemed potentially problematic that E. coli can synthesize a catabolic phenylethylamine oxidase that stoichiometrically generates H 2 O 2 . This study was undertaken to understand how E. coli tolerates the oxidative stress that must ensue. Measurements indicated that phenylethylamine-fed cells generate H 2 O 2 at 30 times the rate of glucose-fed cells. Two tolerance mechanisms were identified. First, in enclosed laboratory cultures, growth on phenylethylamine triggered induction of the OxyR H 2 O 2 stress response. Null mutants (⌬oxyR) that could not induce that response were unable to grow. This is the first demonstration that OxyR plays a role in protecting cells against endogenous H 2 O 2 . The critical element of the OxyR response was the induction of H 2 O 2 scavenging enzymes, since mutants that lacked NADH peroxidase (Ahp) grew poorly, and those that additionally lacked catalase did not grow at all. Other OxyR-controlled genes were expendable. Second, phenylethylamine oxidase is an unusual catabolic enzyme in that it is localized in the periplasm. Calculations showed that when cells grow in an open environment, virtually all of the oxidase-generated H 2 O 2 will diffuse across the outer membrane and be lost to the external world, rather than enter the cytoplasm where H 2 O 2 -sensitive enzymes are located. In this respect, the periplasmic compartmentalization of phenylethylamine oxidase serves the same purpose as the peroxisomal compartmentalization of oxidases in eukaryotic cells.

Primary Amine Oxidase of Escherichia coli Is a Metabolic Enzyme that Can Use a Human Leukocyte Molecule as a Substrate

“…To analyze the relationship between ECAO expression and the presence of both lactose and PEA in the medium, we tested the amine oxidase activity of wt and Δ tynA strains in minimal medium M9 supplemented with lactose, with or without 5 mM PEA. We detected a clear dependence of activity on the presence of lactose and PEA for wt, but the Δ tynA strain had no activity in either ( Fig 1B ), which has been shown before with a different medium [ 18 ]. To measure the amount of H 2 O 2 released into the medium by ECAO, we measured the H 2 O 2 concentrations of stationary phase cultures of wt and Δ tynA strains.…”

“…It is a prototypic homodimer that has a catalytic section consisting of the D2–D4 domains and an additional D1 domain that is absent from other solved copper amine oxidase (CAO) structures. Although ECAO (as well as PrAOs from Arthrobacter globiformis and Hansenula polymorpha ) has been used as a model enzyme to elucidate the enzymatic mechanism of amine oxidases [ 10 – 17 ], its known biological functions have so far been limited to enabling the bacteria to grow on different carbon or nitrogen sources [ 5 , 9 , 18 ]. In mammals, the corresponding primary amine oxidase, hAOC3, is involved in processes such as leukocyte trafficking and glucose metabolism [ 19 ].…”

Antimicrobial activity of iron oxide nanoparticle upon modulation of nanoparticle-bacteria interface

“…In case of IONP, ROS production follow the Fenton reaction as mentioned below in equations 2 and 3. From the metabolic activity, hydrogen peroxide (H 2 O 2 ), which is a toxic oxidant causing DNA and protein damage, is produced in cultures of all aerobic organisms 35 36 . E. coli produces H 2 O 2 at the rate 10–15 μM/s during the growth in oxygen rich glucose medium 36 , as also observed in untreated bacterial culture, Fig.…”

“…In our study, we measured ROS production in culture by the fluorescent dye, DCFH-DA (described in result section). Upon IONPs dispersion inside the culture media, different oxido-reduction reactions are followed involving both the species present in magnetite, Fe 3+ and Fe 2+ , resulting into generation of different and more potent reactive oxygen species 36 37 . The reactions are known as Fenton reaction or Haber-Weiss cycle.…”

Unraveling the Mechanism for the Viability Deficiency of Shewanella oneidensis oxyR Null Mutant

“…H 2 O 2 is ubiquitous because of the existence of diverse ways for its generation, both biologically and abiotically (3). H 2 O 2 , in concert with O 2 Ϫ , is a metabolic by-product of cellular oxygen respiration, mostly through the accidental auto-oxidation of nonrespiratory flavoproteins and the turnover of committed oxidases (4,5). Additionally, many organisms synthesize H 2 O 2 and secrete it into their environment to suppress the growth of potentially competing and/or detrimental microbes (3).…”