Identification of oxygen-independent pathways for pyridine-nucleotide and Coenzyme-A synthesis in anaerobic fungi by expression of candidate genes in yeast

Neocallimastigomycetes are rare examples of strictly anaerobic eukaryotes. This study investigates how these anaerobic fungi bypass reactions involved in synthesis of pyridine nucleotide cofactors and coenzyme A that, in canonical fungal pathways, require molecular oxygen. Analysis of Neocallimastigomycete proteomes identified a candidate L-aspartate-decarboxylase (AdcA), and L-aspartate oxidase (NadB) and quinolinate synthase (NadA), constituting putative oxygen-independent bypasses for coenzyme A synthesis and pyridine nucleotide cofactor synthesis, respectively. The corresponding gene sequences indicated acquisition by ancient horizontal gene transfer event involving bacterial donors. To test whether these enzymes suffice to bypass corresponding oxygen-requiring reactions, they were introduced into fms1Δ and bna2Δ Sacharomyces cerevisiae strains. Expression of nadA and nadB , and adcA from the Neocallimastigomycetes Piromyces finnis and Neocallimastix californiae , respectively, conferred cofactor prototrophy under aerobic and anaerobic conditions. This study simulates how horizontal gene transfer can drive eukaryotic adaptation to anaerobiosis, and provides a basis for elimination of auxotrophic requirements in anaerobic industrial applications of yeasts and fungi. ### Competing Interest Statement The authors have declared no competing interest.