PURINE AND PYRIMIDINE BIOSYNTHESIS IN METHANOGENIC BACTERIA

Following long-term labeling with [1-C-13]acetate, [2-C-13]acetate, (C O2)-C-13, (HCOOH)-C-13, or (CH3OH)-C-13, NMR spectroscopy was used to determine the labeling patterns of the purified ribonucleosides of Met hanospirillum hungatei, Methanococcus voltae, Methanobrevibacter smith ii, Methanosphaera stadtmanae, Methanosarcina barkeri and Methanobacte rium bryantii. Major differences were observed among the methanogens s tudied, specifically at carbon positions 2 and 8 of the purines, posit ions at which one-carbon carriers are involved during synthesis. In Me thanospirillum hungatei and Methanosarcina barkeri, the label at both positions came from carbon atom C-2 of acetate, as predicted from know n eubacterial pathways, whereas in Methanococcus voltae and Methanobac terium bryantii both originated from CO2. In Methanosphaera stadtmanae grown in the presence of formate, the C-2 of purines originated exclu sively from formate and the C-8 was labeled by the C-2 of acetate. Whe n grown in media devoid of formate, the C-2 of the purine ring origina ted mainly from the C-2 of acetate and in part from CH3OH. In Methnnob revibacter smithii grown in the presence of formate, C-2 and C-8 of pu rines were derived from CO2 and/or formate. The labeling patterns obta ined for pyrimidines are consistent with the biosynthetic pathways com mon to eubacteria and eucaryotes.