Cofactor F420 Tail Length Diversity in Specific Representatives of the Class Methanosarcinia During Acetoclastic and Methylotrophic Methanogenesis: Deciphering Structural Variations.

OBJECTIVES: Methanogens possess a variety of coenzymes and cofactors that are involved in redox reactions that occur during methanogenesis. One essential cofactor is F420, a deazaflavin derivate with an oligoglutamate side chain which acts as a low redox potential electron carrier and participates in electron transport coupled with energy conservation. This work aimed at characterizing cofactor F420 analogues in eight distinct acetoclastic and methylotrophic pure cultures of the class Methanosarcinia. METHODS: Pure cultures of Methanothrix soehngenii, Methanothrix thermoacetophila, Methanomethylovorans thermophila, Methanosarcina acetivorans, Methanosarcina flavescens, Methanosarcina lacustris, Methanosarcina spelaei, and Methanosarcina thermophila were cultivated under strict anaerobic conditions and analysed regarding various physiological parameters. Cofactor F420 was extracted via solid phase extraction and analysed via ion-pair reversed-phase HPLC. RESULTS: The study showed that methylotrophic organisms tended to exhibit a greater variety of distinct cofactor F420 glutamyl chain lengths than the obligately acetoclastic ones. The shortest average glutamyl chain length and the highest F420 yields were detected in Methanomethylovorans thermophila and Methanosarcina acetivorans - both incapable of internal H2 cycling which is present in the other investigated methanogens, whereas the longest chains were observed in Methanosarcina thermophila. Additionally, the total cofactor F420 concentration increased during the cultivation period of methanogens capable of methylotrophic methanogenesis, whereas no notable increase was detected in exclusively acetoclastic ones. CONCLUSIONS: These phenotypic comparisons further expand our understanding of how F420 tail length correlates with taxonomy and physiology, providing another puzzle piece toward a comprehensive picture of fundamental biochemical mechanisms in methanogens while establishing a baseline for biotechnological strategies on a yet distant horizon.