Hydrogen thresholds and steady-state concentrations associated with microbial arsenate respiration.
H2 thresholds for microbial respiration of arsenate (As(V)) were investigated in a pure culture of Sulfurospirillum arsenophilum. H2 was consumed to threshold concentrations of 0.03-0.09 nmol/L with As(V) as terminal electron acceptor, allowing for a Gibbs free-energy yield of 36-41 kJ per mol of reaction. These thresholds are among the lowest measured for anaerobic respirers and fall into the range of denitrifiers or Fe(III)-reducers. In sediments from an arsenic-contaminated aquifer in the Red River flood plain, Vietnam, H2 levels decreased to 0.4-2 nmol/L when As(V) was added under anoxic conditions. When As-(V) was depleted, H2 concentrations rebounded by a factor of 10, a level similar to that observed in arsenic-free controls. The sediment-associated microbial population completely reduced millimolar levels of As(V) to arsenite (As-(III)) within a few days. The rate of As(V)-reduction was essentially the same in sediments amended with a pure culture of S. arsenophilum. These findings together with a review of observed H2 threshold and steady-state values suggest that microbial As(V)-respirers have a competitive advantage over several other anaerobic respirers through their ability to thrive at low H2 levels.
Heimann
Axel C
AC
Institute of Environment & Resources, Bygningstorvet, Building 115, Technical University of Denmark, DK-2800 Lyngby, Denmark. axh@er.dtu.dk
Blodau
Christian
C
Postma
Dieke
D
Larsen
Flemming
F
Viet
Pham H
PH
Nhan
Pham Q
PQ
Jessen
Søren
S
Duc
Mai T
MT
Hue
Nguyen T M
NT
Jakobsen
Rasmus
R
D001149:Arsenates / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002849:Chromatography, Gas; D004785:Environmental Pollutants / Q000378:metabolism*; D020565:Epsilonproteobacteria / Q000378:metabolism*; D019015:Geologic Sediments / Q000032:analysis*; D006859:Hydrogen / Q000378:metabolism*; D008697:Methane / Q000378:metabolism; D013816:Thermodynamics; D014744:Vietnam
D001149:Arsenates; D004785:Environmental Pollutants; D006859:Hydrogen; C025657:arsenic acid; D008697:Methane