The strictly anaerobic methanogen Methanosarcina barkeri strain Fusaro (DSM 804) was fermented on a 3-liter scale in a CSTR (continuous stirred tank reactor) to obtain almost 10 g biomass dry weight per day. The generation time of the microorganism with methanol as the sole carbon source was 6.0 h, the maximal growth rate 0.115 h−1 correspondingly.
In cell-free extracts from the fermented organism active hydrogenases were found. They reduced methyl viologen (MV⊕⊕), an artificial electron acceptor, molecular hydrogen being the substrate. This reaction was used to get electrochemical energy in a biochemical fuel cell. The maximum output of this fuel cell was 2.6 mW.
Furthermore, cell-free extracts from M. barkeri showed alcohol dehydrogenase activity under aerobic conditions when N,N′-dimethyl-4-nitrosoaniline (NDMA) was used as an artificial electron acceptor. The NDMA-dependent alcohol dehydrogenase (NDMA-ADH) was purified to homogeneity by column chromatography. It is a homodimeric enzyme consisting of subunits of 45 kDa, the native molecular mass is about 87 kDa. The enzyme is independent of free coenzyme such as NAD, NADP, FMN, FAD and F420, but it possesses a tightly but noncovalently bound NADP(H) cofactor.
The purified enzyme exhibited activity only with primary alcohols including aromatic alcohols, but methanol was not accepted. It also catalyzed the stoichiometric dismutation of aldehydes, especially long-chain aldehydes, to form a half mol of each of the corresponding alcohol and acid without addition of an electron carrier. NDMA-ADH from M. barkeri is a novel type of nicotinoprotein in methanogenic bacteria.