Function of Periplasmic Hydrogenases in the Sulfate-Reducing Bacterium Desulfovibrio vulgaris Hildenborough

Abstract

The sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough possesses four periplasmic hydrogenases to facilitate the oxidation of molecular hydrogen. These include an [Fe] hydrogenase, an [NiFeSe] hydrogenase, and two [NiFe] hydrogenases encoded by the hyd, hys, hyn1, and hyn2 genes, respectively. In order to understand their cellular functions, we have compared the growth rates of existing (hyd and hyn1) and newly constructed (hys and hyn-1 hyd) mutants to those of the wild type in defined media in which lactate or hydrogen at either 5 or 50% (vol/vol) was used as the sole electron donor for sulfate reduction. Only strains missing the [Fe] hydrogenase were significantly affected during growth with lactate or with 50% (vol/vol) hydrogen as the sole electron donor. When the cells were grown at low (5% [vol/vol]) hydrogen concentrations, those missing the [NiFeSe] hydrogenase suffered the greatest impairment. The growth rate data correlated strongly with gene expression results obtained from microarray hybridizations and real-time PCR using mRNA extracted from cells grown under the three conditions. Expression of the hys genes followed the order 5% hydrogen > 50% hydrogen > lactate, whereas expression of the hyd genes followed the reverse order. These results suggest that growth with lactate and 50% hydrogen is associated with high intracellular hydrogen concentrations, which are best captured by the higher activity, lower affinity [Fe] hydrogenase. In contrast, growth with 5% hydrogen is associated with a low intracellular hydrogen concentration, requiring the lower activity, higher affinity [NiFeSe] hydrogenase.Hydrogen is intimately involved in the metabolism of sulfate-reducing bacteria (SRB) of the genus Desulfovibrio (17). In addition to utilizing molecular hydrogen directly as an electron donor for sulfate reduction, hydrogen may play a central role as an intermediate in the generation of a chemiosmotic gradient from the oxidation of organic molecules. This process has become known as hydrogen cycling (18). The current emphasis on developing more efficient energy production strategies has made understanding SRB metabolism a critical endeavor, especially with respect to the SRB connection with hydrogen and the impact of SRB on the petroleum industry through oil reservoir souring and pipeline corrosion.Hydrogenases catalyze the heterolytic cleavage of molecular hydrogen into protons and electrons (H 2 7 2H ϩ ϩ 2e) (9). These enzymes are present ubiquitously in both Archaea and Bacteria, including many SRB. The fully sequenced Desulfovibrio vulgaris Hildenborough has a total of six hydrogenases (14). Four of them are periplasmic and therefore presumably are involved in hydrogen oxidation, including a soluble iron-only [Fe] hydrogenase (Hyd) (16), two membrane-associated nickel-iron [NiFe] hydrogenase isozymes (Hyn1 and Hyn2) (14, 23), and a membrane-associated nickel-iron-selenium [NiFeSe] hydrogenase (Hys) (31). The [NiFe] hydrogenases are widely distributed in SRB (35), but many Desulfovibri...

H2metabolism is widespread and diverse among human colonic microbes

“…These ubiquitous enzymes are found in Archaea, Bacteria, and some Eukarya, and include both anaerobically-and aerobically-adapted variants. 7,19 In anoxic environments such as the human colon, hydrogenases can potentially conserve energy through 3 major processes: 1) hydrogenotrophic respiration by coupling oxidation of the high-energy fuel H 2 to the reduction of exogenous oxidants such as sulfate; 20,21 2) hydrogenogenic fermentation by coupling oxidation of ferredoxin or formate to the production of the dissipatable H 2 ; 22,23 or 3) hydrogenogenic respiration by coupling ferredoxin oxidation to proton reduction in cationtranslocating complexes. 24,25 More recently, a fourth mechanism of H 2 -dependent energy conservation has been described in acetogens and methanogens: flavinbased electron bifurcation.…”

Roles of HynAB and Ech, the Only Two Hydrogenases Found in the Model Sulfate Reducer Desulfovibrio gigas

“…Thus, as suggested before, the mechanism of hydrogen cycling does not seem to be strictly essential for the Desulfovibrio genus (9) and may make different contributions to the overall electron flow in different organisms. This is not entirely surprising since it was previously shown that some SRB do not have any hydrogenases at all (e.g., Desulfococcus oleovorans) or have no cytoplasmic hydrogenases (like Desulfomicrobium baculatum, which is closely related to Desulfovibrionaceae) (6).…”

“…Furthermore, the function of each hydrogenase in terms of hydrogen production or oxidation may vary depending on the conditions presented to the cell. Numerous studies have reported hydrogenase mutant strains of Desulfovibrio fructosovorans and in D. vulgaris Hildenborough (9,(14)(15)(16)(17). However, in most cases, because of the multiplicity of enzymes present, these studies were not conclusive.…”

“…In addition, the expression patterns of different hydrogenases were shown to be different and to depend on the substrate, fermentative or respiratory growth, or metal availability (5,(7)(8)(9)(10)(11)(12)(13). Furthermore, the function of each hydrogenase in terms of hydrogen production or oxidation may vary depending on the conditions presented to the cell.…”

Nickel–Iron–Selenium Hydrogenases – An Overview

“…However, when selenium is available there is a strong downregulation of both Hyn and Hyd Hases and a strong increase in the level of the Hys Hase [46] . [47] .…”