Affiliation:
1. Department of Microbiology, University of Washington, Seattle, Washington
Abstract
ABSTRACT
Reduced coenzyme F
420
(F
420
H
2
) is an essential intermediate in methanogenesis from CO
2
. During methanogenesis from H
2
and CO
2
, F
420
H
2
is provided by the action of F
420
-reducing hydrogenases. However, an alternative pathway has been proposed, where H
2
-dependent methylenetetrahydromethanopterin dehydrogenase (Hmd) and F
420
H
2
-dependent methylenetetrahydromethanopterin dehydrogenase (Mtd) together reduce F
420
with H
2
. Here we report the construction of mutants of
Methanococcus maripaludis
that are defective in each putative pathway. Their analysis demonstrates that either pathway supports growth on H
2
and CO
2
. Furthermore, we show that during growth on formate instead of H
2
, where F
420
H
2
is a direct product of formate oxidation, H
2
production occurs. H
2
presumably arises from the oxidation of F
420
H
2
, and the analysis of the mutants during growth on formate suggests that this too can occur by either pathway. We designate the alternative pathway for the interconversion of H
2
and F
420
H
2
the Hmd-Mtd cycle.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology