Comparative Genomic Analysis and Data About the Metabolism of the Genus Sphaerotilus Provide the First Evidence of Methylotrophic Growth and Reveal Two Strategies of Methanol Oxidation and C1 Compound Assimilation

For the first time in this study, the ability for methylotrophic growth on methanol was demonstrated in representatives of the genus Sphaerotilus. The analysis of 20 genomes and the physiological verification of genomic predictions regarding C1 compound metabolism were carried out using Sphaerotilus montanus HST, Sphaerotilus hippei DSM 566T, and Sphaerotilus sulfidivorans D-501T as model strains. Genes involved in the direct oxidation of methanol to carbon dioxide were identified, including the lanthanide-dependent methanol dehydrogenase XoxF, the NAD-dependent methanol dehydrogenase Mdh2, genes of the tetrahydromethanopterin (H4MPT) and tetrahydrofolate (H4F) pathways, and the NAD-dependent formate dehydrogenase. In addition, a number of genes associated with C1 assimilation were identified, including genes of the Calvin–Benson–Bassham cycle and the incomplete serine cycle. Experimental data suggest that the bacteria are capable of using two strategies of methylotrophic growth: methanol oxidation via the lanthanide-dependent methanol dehydrogenase XoxF and the H4MPT pathway, as well as oxidation via the NAD-dependent methanol dehydrogenase Mdh2 and the H4F pathway. Both strategies provide CO2 assimilation via the Calvin–Benson–Bassham, but additionally the second strategy demonstrates additional involvement of the incomplete serine cycle in the process of the C1 compounds. A hypothetical model of C1 compound assimilation in representatives of the genus Sphaerotilus was constructed.