| Abstract | Following long-term labeling with [1-13C]acetate, [2-13C]acetate, 13CO2, H13COOH, or 13CH3OH, NMR spectroscopy was used to determine the labeling patterns of the purified ribonucleosides of Methanospirillum hungatei, Methanococcus voltae, Methanobrevibacter smithii, Methanosphaera stadtmanae, Methanosarcina barkeri and Methanobacterium bryantii. Major differences were observed among the methanogens studied, specifically at carbon positions 2 and 8 of the purines, positions at which one-carbon carriers are involved during synthesis. In Methanospirillum hungatei and Methanosarcina barkeri, the labcl at both positions came from carbon atom C-2 of acetate, as predicted from known eubacterial pathways, whereas in Methanococcus voltae and Methanobacterium bryantii both originated from CO2. In Methanosphaera stadtmanae grown in the presence of formate, the C-2 of purines originated exclusively from formate and the C-8 was labeled by the C-2 of acetate. When grown in media devoid of formate, the C-2 of the purine ring originated mainly from the C-2 of acetate and in part from CH3OH. In Methanobrevibacter smithii grown in the presence of formate, C-2 and C-8 of purines were derived from CO2 and/or formate. The labeling patterns obtained for pyrimidines are consistent with the biosynthetic pathways common to eubacteria and eucaryotes. |
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