Abstract
The metabolic pathways of one-carbon compounds utilized by colorless sulfur bacterium Beggiatoa leptomitoformis D-402 were revealed based on comprehensive analysis of its genomic organization, together with physiological, biochemical and molecular biological approaches. Strain D-402 was capable of aerobic methylotrophic growth with methanol as a sole source of carbon and energy and was not capable of methanotrophic growth because of the absence of genes of methane monooxygenases. It was established that methanol can be oxidized to CO2 in three consecutive stages. On the first stage methanol was oxidized to formaldehyde by the two PQQ (pyrroloquinolinequinone)-dependent methanol dehydrogenases (MDH): XoxF and Mdh2. Formaldehyde was further oxidized to formate via the tetrahydromethanopterin (H4MPT) pathway. And on the third stage formate was converted to CO2 by NAD+-dependent formate dehydrogenase Fdh2. Finally, it was established that endogenous CO2, formed as a result of methanol oxidation, was subsequently assimilated for anabolism through the Calvin-Benson-Bassham cycle. The similar way of one-carbon compounds utilization also exists in representatives of another freshwater Beggiatoa species-B. alba.