TY - JOUR
T1 - Hydrogen is a preferred intermediate in the energy-conserving electron transport chain of Methanosarcina barkeri
AU - Kulkarni, Gargi
AU - Kridelbaugh, Donna M.
AU - Guss, Adam M.
AU - Metcalf, William W.
PY - 2009/9/15
Y1 - 2009/9/15
N2 - Methanogens use an unusual energy-conserving electron transport chain that involves reduction of a limited number of electron acceptors to methane gas. Previous biochemical studies suggested that the proton-pumping F 420H2 dehydrogenase (Fpo) plays a crucial role in this process during growth on methanol. However, Methanosarcina barkeri Δfpo mutants constructed in this study display no measurable phenotype on this substrate, indicating that Fpo plays a minor role, if any. In contrast, Δfrh mutants lacking the cytoplasmic F420-reducing hydrogenase (Frh) are severely affected in their ability to grow and make methane from methanol, and double Δfpo/Δfrh mutants are completely unable to use this substrate. These data suggest that the preferred electron transport chain involves production of hydrogen gas in the cytoplasm, which then diffuses out of the cell, where it is reoxidized with transfer of electrons into the energy-conserving electron transport chain. This hydrogen-cycling metabolism leads directly to production of a proton motive force that can be used by the cell for ATP synthesis. Nevertheless, M. barkeri does have the flexibility to use the Fpo-dependent electron transport chain when needed, as shown by the poor growth of the Δfrh mutant. Our data suggest that the rapid enzymatic turnover of hydrogenases may allow a competitive advantage via faster growth rates in this freshwater organism. The mutant analysis also confirms the proposed role of Frh in growth on hydrogen/carbon dioxide and suggests that either Frh or Fpo is needed for aceticlastic growth of M. barkeri.
AB - Methanogens use an unusual energy-conserving electron transport chain that involves reduction of a limited number of electron acceptors to methane gas. Previous biochemical studies suggested that the proton-pumping F 420H2 dehydrogenase (Fpo) plays a crucial role in this process during growth on methanol. However, Methanosarcina barkeri Δfpo mutants constructed in this study display no measurable phenotype on this substrate, indicating that Fpo plays a minor role, if any. In contrast, Δfrh mutants lacking the cytoplasmic F420-reducing hydrogenase (Frh) are severely affected in their ability to grow and make methane from methanol, and double Δfpo/Δfrh mutants are completely unable to use this substrate. These data suggest that the preferred electron transport chain involves production of hydrogen gas in the cytoplasm, which then diffuses out of the cell, where it is reoxidized with transfer of electrons into the energy-conserving electron transport chain. This hydrogen-cycling metabolism leads directly to production of a proton motive force that can be used by the cell for ATP synthesis. Nevertheless, M. barkeri does have the flexibility to use the Fpo-dependent electron transport chain when needed, as shown by the poor growth of the Δfrh mutant. Our data suggest that the rapid enzymatic turnover of hydrogenases may allow a competitive advantage via faster growth rates in this freshwater organism. The mutant analysis also confirms the proposed role of Frh in growth on hydrogen/carbon dioxide and suggests that either Frh or Fpo is needed for aceticlastic growth of M. barkeri.
KW - F
KW - H cycling
KW - Hydrogen electron transport
KW - Methanogenesis
UR - http://www.scopus.com/inward/record.url?scp=70349468045&partnerID=8YFLogxK
U2 - 10.1073/pnas.0905914106
DO - 10.1073/pnas.0905914106
M3 - Article
C2 - 19805232
AN - SCOPUS:70349468045
SN - 0027-8424
VL - 106
SP - 15915
EP - 15920
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 37
ER -