Energy Generation and Utilization in Hydrogen Bacteria

Abstract

Studies on the relationship between cell synthesis and energy utilization in Hydrogenomonas eutropha have shown that the amount of oxidative energy required for synthetic reactions depends on the conditions of growth. The energy of hydrogen oxidation was most efficiently used when growth conditions were optimal (continuous culture, cells in exponential growth phase) and when the rate of growth was limited by H2 or 02 supply. Under these conditions, 2 to 2.5 atoms of oxygen were consumed by the oxyhydrogen reaction for the concomitant conversion of 1 mole of CO2 to cell matter. This conversion efficiency, expressed as the O/C energyyield value, was observed with continuous cultures. A less efficient conversion was found with batch cultures. With limiting concentrations of CO2 the rate of hydrogen oxidation was relatively high, and the O/C value was dependent on the growth rate. With nonlimiting concentrations of CO2, the rate of hydrogen oxidation was strictly proportional to the rate of CO2 fixation, and the O/C value was independent of growth rate. This proportionality between the rate of H2 oxidation and the rate of CO2 fixation suggested that energy supply regulates the (maximum) rate of growth. From the energy-yield measurements, we concluded that the oxidation of 1 mole of H2 yields the equivalent of 2 moles of adenosine triphosphate for H. eutropha, and that at least 5 moles of this high-energy phosphate is required for the conversion of 1 mole of CO2 into cellular constituents.

Linking geology, fluid chemistry, and microbial activity of basalt‐ and ultramafic‐hosted deep‐sea hydrothermal vent environments

“…Despite similar temperature and chemical compositions of Clueless and Desperate hydrothermal fluids, also different energy sources appeared to fuel autotrophic CO 2 fixation. Estimated ratios of hydrogen oxidation to CO 2 fixation rates in the oxic hydrogen-spiked Clueless incubations (Table S1) were close to ratios common for hydrogen-oxidizing autotrophs (Ruhland, 1924;Bongers, 1970;Perner et al, 2010). In contrast, sulfide removal to CO 2 fixation rate ratios in most sulfide-spiked Desperate incubations (Table S1) were close to the ratio expected for energy dissipation (Tr€ uper, 1964;Sorokin, 1972) arguing for sulfide oxidation providing the energy for autotrophic biomass synthesis (Perner et al, 2011).…”

“…Consequently, hydrogen concentrations in the Wideawake and Foggy Corner environment may be so low because hydrogen has been consumed along the fluid flow pathway. The ratios of hydrogen oxidation to CO 2 fixation rates (Table S1) estimated from the Wideawake and Foggy Corner incubation experiments exceeded those that would be expected if hydrogen oxidation was providing the energy for CO 2 fixation (Ruhland, 1924;Bongers, 1970) and is thus indicative of heterotrophic hydrogen oxidizers in the hydrogen-spiked incubations. While in the Wideawake incubations hydrogen concentrations were accompanied by considerable cell growth, cell numbers in the hydrogenspiked Foggy Corner incubations remained mostly unchanged and resembled those of the environment (Fig.…”

Geochemical constraints on the diversity and activity of H2-oxidizing microorganisms in diffuse hydrothermal fluids from a basalt- and an ultramafic-hosted vent

“…3c and d). Estimated ratios for autotrophically growing H 2 -oxidizing bacteria (Ruhland, 1924;Bongers, 1970) suggest that more H 2 is being consumed in the Clueless H 2 -spiked oxic incubations (Table S1) than would be required when coupling H 2 oxidation to CO 2 fixation. In the Clueless incubations, H 2 availability alone is likely not the prime determinant for stimulating CO 2 fixation as (1) no CO 2 was fixed in the anoxic incubations despite H 2 addition and (2) CO 2 fixation was also stimulated in some unamended incubations ( Fig.…”

Metabolic engineering in chemolithoautotrophic hosts for the production of fuels and chemicals

“…Furthermore, transfer of R. eutropha SH 540 genes into Pseudomonas facilis (containing MBH) reduced its doubling time from 12 to 9 h 541 (Friedrich & Schwartz, 1993). This is likely also reflected in apparent H 2 yield of R. eutropha of 542 6.4 gDW/mol-H 2 (Bongers, 1970) versus only 2.7 for R. capsulatus (Siegel & Ollis, 1984). 543…”