An examination of the methanofurans isolated from a wide range of methanogenic bacteria and from Archaeoglobus fulgidus has revealed at least five chromatographically distinct methanofurans. Bacteria from each major genus of methanogenic bacteria have been found to contain a chemically different methanofuran. The nature of the differences in the methanofurans appears to lie in the modification of the side chain attached to the basic core structure of 4-[N-(-y-L-glutamyl--y-L-glutamyl)-p-(,-aminoethyl)phenoxymethyl]-2-(aminomethyl)furan. This was supported by the structural elucidation of the methanofuran isolated from Methanobrevibacter smithii, designated methanofuran-c, which was the same as the originally characterized methanofuran except for a hydroxy group at the 2 position of the 4,5-dicarboxyoctanedioic acid moiety of the molecule.Methanofuran (Fig. 1) is a recently characterized cofactor in the conversion of CO2 to methane by methanogenic bacteria (9-11). It is involved in the first step of CO2 reduction, where it serves as a C1 carrier at the formyl level of carbon oxidation (7,10 aminomethyl)furan with different attached side chain molecules. This is supported by the structural analysis of the methanofuran from Methanobrevibacter smithii, which shows it to consist of this basic core structure, peptide bonded, via the terminal glutamyl residue, to the C-1 of 2-hydroxy-4,5-dicarboxyoctanedioic acid (2-hydroxyDCO) (Fig. 1).
MATERIALS AND METHODSBacterial strains and growth. Methanobacterium formicicum JF-1, Methanobacterium bryantii MOH, and Methanospirillum hungatei JF were grown in 10-liter batches on a medium modified from Schauer and Ferry (15), consisting of 1.44 g of NH4C1, 1.14 g of K2HPO4, 1.14 g of KH2PO4, 0.5 g of yeast extract (Difco Laboratories, Detroit, Mich.), 0.5 g of tryptone (Difco), 6.0 g of sodium formate, 2.0 g of sodium acetate, 0.01 g of Fe(NH4)SO4, 5.0 g of Na2HCO3, 0.001 g of resazurin, 0.46 g of NaCl, 0.092 g of MgCl2 6H20, 0.26 g of CaCl2 .2H20, 0.25 g of cysteine hydrochloride, and 0.25 g of Na2S 9H20 per liter of water. In addition, vitamin and trace mineral solutions (2) were each added to a final 2% (vol/vol) concentration. Methanobrevibacter smithii PS was grown in 3-liter batches on a medium modified from that of Lovley et al. (13), consisting of 0.45 g of K2HPO4, 0.15 g of KH2PO4, 0.12 g of NH4C1, 0.3 g of NaCl, 0.04 g of CaCl2 2H20, 2.5 g of NaHCO3, 0.14 g of MgCl2 6H20, 2.5 g of sodium acetate, 5.0 g of sodium formate, 2.0 g of yeast extract, 2.0 g of tryptone, 0.0001 g of resazurin, 0.5 g of cysteine hydrochloride, and 0.5 g of Na2S 9H20 per liter of water. Also added were antifoam C, 0.0005% (vol/vol); vitamin and trace mineral solutions (2), 1% each (vol/vol); iosbutyric, 2-methylbutyric, isovaleric, and valeric acids, each to a final concentration of 0.0005% (vol/vol); and Tween 80, 0.002% (vol/vol).Methanococcus maripaludis JJ was provided by William B. Whitman, Department of Microbiology, University of Georgia, Athens. The organism was grown by Whitman on a comple...