Distribution of Lysine Pathways Among Fungi: Evolutionary Implications

With the aid of diagnostic radiocarbon tracers, lysine synthesis was studied in representatives of 21 orders of basidiomycetes, ascomycetes, and phycomycetes. The labeling pattern corresponding to the α-aminoadipic acid-lysine path was given by all basidiomycetes and ascomycetes and by those phycomycetes which produce non-flagellate or posteriorly uniflagellate spores. The pattern characteristic of the α,ε-diaminopimelic acid-lysine path was shown by those phycomycetes which produce anteriorly uniflagellate or biflagellate spores. The remarkable consistency of the distribution of the two lysine paths suggests that (a) they did not arise sporadically; (b) their distribution pattern was not disturbed by genetic exchange; and (c) there is a substantial evolutionary gap in organisms differing in path of lysine synthesis. Neither lysine path is thought to have emerged in an organism possessing the other. The α,ε-diaminopimelic acid path may be the more ancient. A common evolutionary precursor of organisms having the α-aminoadipic acid path is postulated; these organisms include euglenids as the only non-fungal forms known to have this path. The inferred common precursor is viewed as a lysine-non-producing, animal-like organism in an evolutionary line that had branched off the main stream of evolution of the plant kingdom