Why do bacteria use so many enzymes to scavenge hydrogen peroxide?

Abstract

Hydrogen peroxide (H2O2) is continuously formed by the autoxidation of redox enzymes in aerobic cells, and it also enters from the environment, where it can be generated both by chemical processes and by the deliberate actions of competing organisms. Because H2O2 is acutely toxic, bacteria elaborate scavenging enzymes to keep its intracellular concentration at nanomolar levels. Mutants that lack such enzymes grow poorly, suffer from high rates of mutagenesis, or even die. In order to understand how bacteria cope with oxidative stress, it is important to identify the key enzymes involved in H2O2 degradation. Catalases and NADH peroxidase (Ahp) are primary scavengers in many bacteria, and their activities and physiological impacts have been unambiguously demonstrated through phenotypic analysis and through direct measurements of H2O2 clearance in vivo. Yet a wide variety of additional enzymes have been proposed to serve similar roles: thiol peroxidase, bacterioferritin comigratory protein, glutathione peroxidase, cytochrome c peroxidase, and rubrerythrins. Each of these enzymes can degrade H2O2 in vitro, but their contributions in vivo remain unclear. In this review we examine the genetic, genomic, regulatory, and biochemical evidence that each of these is a bona fide scavenger of H2O2 in the cell. We also consider possible reasons that bacteria might require multiple enzymes to catalyze this process, including differences in substrate specificity, compartmentalization, cofactor requirements, kinetic optima, and enzyme stability. It is hoped that the resolution of these issues will lead to an understanding of stress resistance that is more accurate and perceptive.

Antibiotics induce redox-related physiological alterations as part of their lethality

“…2D). We quantified GFP expression induction over a range of H 2 O 2 concentrations spanning six orders of magnitude (1 mM-1 nM), which encompasses the minimum levels of H 2 O 2 reported to fully oxidize OxyR both in vivo (5 μM) and in vitro (50 nM, in the presence of antioxidants) (61,65). Significant changes in pOxySgfp expression were detected at a threshold near 1 μM H 2 O 2 as compared with untreated cells; this finding is consistent with reports of OxyR activation by submicromolar H 2 O 2 (66,67).…”

The antagonistic and synergistic effects of temperature during solar disinfection of synthetic secondary effluent

“…(Chiang and Schellhorn, 2012) and others, all related by the ROS production inside and outside the cell. ROS are normal by-products of bacterial respiratory chain, and bacteria possess a big number of suppressive mechanisms (Mishra and Imlay, 2012) [56,57]. Hence, UVA damage is an internal/external oxidative damage, plus the internal/external photo-Fenton contribution, with measurable effects; an increase in dose can inflict greater damage [10].…”

Insights into the Function of a Second, Nonclassical Ahp Peroxidase, AhpA, in Oxidative Stress Resistance in Bacillus subtilis

“…To combat the damage generated by ROS, bacteria produce numerous enzymes to scavenge toxic oxygen molecules (4)(5)(6). For peroxides specifically, bacteria produce numerous catalases and peroxidases to scavenge H 2 O 2 and organic peroxide molecules.…”

“…While it is clear that bacteria must protect themselves against the damaging effects of peroxides, it is not understood why bacteria, lacking the multiple organelle-derived compartments present in eukaryotes, have so many enzymes that appear to be designed to scavenge peroxides (5). In B. subtilis, for example, there are potentially nine enzymes with peroxide-scavenging activity.…”