Structural characteristics of methanogenic cofactors in the non-methanogenic archaebacterium Archaeoglobus fulgidus

Archaeoglobus fulgidus is an extremely thermophilic, sulphate reducing archaebacterium thought to represent a biochemical missing-link between sulphur-metabolizing bacteria and methanogenic bacteria. Whereas the phylogenetic position of A.fulgidus is closer to the sulphur-metabolizing bacteria, there is a partial overlap in the biochemical machinery of A.fulgidus with both groups of bacteria. In particular, the presence of a number of aberrant cofactors up to now thought to be involved exclusively in the process of methanogenesis in methanogenic archaebacteria, i.e. coenzyme F420, methanofuran and methanopterin, has been indicated by previous studies. Here we present evidence for the structural identity of the methanopterin cofactor of A.fulgidus with the methanopterin isolated from Methanobacterium thermoautotrophicum and show that this non-methanogenic bacterium contains two as yet unknown analogues of coenzyme F420. The levels of the various cofactors were determined in cultures grown either on formate or lactate as the carbon source and sulphate or thiosulphate as the sulphur source.