Manganese import is a key element of the OxyR response to hydrogen peroxide in Escherichia coli

Abstract

SummaryVery little manganese is imported into Escherichia coli under routine growth conditions: the import system is weakly expressed, the manganese content is low, and a manganese-dependent enzyme is not correctly metallated. Mutants that lack MntH, the importer, grow at wild-type rates, indicating that manganese plays no critical role. However, MntH supports the growth of iron-deficient cells, suggesting that manganese can substitute for iron in activating at least some metalloenzymes. MntH is also strongly induced when cells are stressed by hydrogen peroxide. This adaptation is essential, as E. coli cannot tolerate peroxide stress if mntH is deleted. Other workers have observed that manganese improves the ability of a variety of microbes to tolerate oxidative stress, and the prevailing hypothesis is that manganese does so by chemically scavenging hydrogen peroxide and/or superoxide. We found that manganese does not protect peroxide-stressed cells by scavenging peroxide. Instead, the beneficial effects of manganese correlate with its ability to metallate mononuclear enzymes. Because ironloaded enzymes are vulnerable to the Fenton reaction, the substitution of manganese may prevent protein damage. Accordingly, during H 2O2 stress, mutants that cannot import manganese and/or are unable to sequester iron suffer high rates of protein oxidation.

Protein damage and death by radiation in Escherichia coli and Deinococcus radiodurans

“…Hence, the active component apparently is a low molecular weight entity that does not discriminate between the proteome of E. coli and D. radiodurans. The radioresistance of several bacteria has been shown to correlate with intracellular Mn ++ /Fe ++ concentration ratios (10,(13)(14)(15). Hence, the protective components in extracts of D. radiodurans may include manganese complexes that attenuate the iron-catalyzed Fenton reaction, a major source of *OH radicals (13,14).…”

Control of bacterial iron homeostasis by manganese

“…The Mn 2+ transporter MntH is required for growth of irondeficient cells in E. coli, which has been interpreted to mean that manganese can substitute for iron in activating mononuclear enzymes (6). In that case, iron deficiency creates a need for manganese import to compensate for the lack of iron.…”

“…PerR is much less sensitive to H 2 O 2 under low-iron conditions, when Mn 2+ occupies the regulatory metal site (11). Divalent iron and manganese share similar sizes and coordination geometries, but the total cellular iron content is in excess of manganese in E. coli cells (6,12). A regulatory role for manganese must accommodate this discrepancy, otherwise it would be out-competed by iron.…”

“…Growth of an Escherichia coli iron-transport mutant is inhibited in an mntH background, suggesting that manganese may substitute for iron in cells (6). The mntH and sitABCD genes are transcriptionally regulated by iron as well as by manganese in the model organisms E. coli, Salmonella enterica, and Bacillus subtilis (7)(8)(9).…”

“…Ferrous iron can react with H 2 O 2 to form the very reactive hydroxyl radical. It has been proposed that manganese may substitute for iron in mononuclear enzymes to prevent iron-catalyzed oxidative damage at those sites (6). The peroxide sensor PerR from B. subtilis senses H 2 O 2 through a bound Fe 2+ moiety that catalyzes the oxidation of a histidine residue to inactivate the protein and derepress the expression of genes needed to manage oxidative stress (10).…”