OXIDATION-REDUCTION OF METHANOL, FORMALDEHYDE, SERINE, AND FORMATE INMETHANOSPHAERA-STADTMANAE USING C-14 SHORT-TERM AND LONG-TERM LABELING

Methanosphaera stadtmanae derives its energy from the reduction by H-2 of CH3OH, but not CO2, indicating there is a block in the CO2 methano genesis pathway. Both (CH4)-C-14 and (CO2)-C-14 production were detect ed in whole cells using [C-14]formaldehyde or [C-14]serine as substrat e. (CO2)-C-14 was also observed from [C-14]formate in both whole cells and cofactor-depleted cell-free extracts, and NADP-dependent formate dehydrogenase activity was detected. Both formate and serine blocked t he formation of (CO2)-C-14 from formaldehyde in whole cells. The resul ts confirmed that enzymes involved in the reduction of carbon from the level of methylene-tetrahydromethanopterin in a common methanogenic p athway and a tetrahydromethanopterin-dependent serine hydroxymethyltra nsferase were present in this organism. However, the production of (CH 4)-C-14 could not be observed from [C-14]formate or (CO2)-C-14 plus H- 2. [C-14]Formate was incorporated specifically into histidine and RNA. [C-14]Methanol was also found to label rRNA and cytoplasmic proteins, especially corrinoid proteins.