Disruption of the operon encoding Ehb hydrogenase limits anabolic CO2 assimilation in the archaeon Methanococcus maripaludis.
Methanococcus maripaludis is a mesophilic archaeon that reduces CO2 to methane with H2 or formate as an energy source. It contains two membrane-bound energy-conserving hydrogenases, Eha and Ehb. To determine the role of Ehb, a deletion in the ehb operon was constructed to yield the mutant, strain S40. Growth of S40 was severely impaired in minimal medium. Both acetate and yeast extract were necessary to restore growth to nearly wild-type levels, suggesting that Ehb was involved in multiple steps in carbon assimilation. However, no differences in the total hydrogenase specific activities were found between the wild type and mutant in either cell extracts or membrane-purified fractions. Methanogenesis by resting cells with pyruvate as the electron donor was also reduced by 30% in S40, suggesting a defect in pyruvate oxidation. CO dehydrogenase/acetyl coenzyme A (CoA) synthase and pyruvate oxidoreductase had higher specific activities in the mutant, and genes encoding these enzymes, as well as AMP-forming acetyl-CoA synthetase, were expressed at increased levels. These observations support a role for Ehb in anabolic CO2 assimilation in methanococci.
Porat
Iris
I
Department of Microbiology, University of Georgia, Athens, Georgia 30602-2605, USA.
Kim
Wonduck
W
Hendrickson
Erik L
EL
Xia
Qiangwei
Q
Zhang
Yi
Y
Wang
Tiansong
T
Taub
Fred
F
Moore
Brian C
BC
Anderson
Iain J
IJ
Hackett
Murray
M
Leigh
John A
JA
Whitman
William B
WB
D000106:Acetate-CoA Ligase / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D017353:Gene Deletion; D019766:Genes, Archaeal / Q000235:genetics; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D008697:Methane / Q000378:metabolism; D017017:Methanococcus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D009876:Operon; D020543:Proteome / Q000378:metabolism; D050743:Pyruvate Synthase / Q000378:metabolism
D009097:Multienzyme Complexes; D020543:Proteome; D002245:Carbon Dioxide; D006864:Hydrogenase; D000445:Aldehyde Oxidoreductases; D050743:Pyruvate Synthase; C019823:carbon monoxide dehydrogenase; D000106:Acetate-CoA Ligase; D008697:Methane