Methanol dehydrogenase is a key enzyme in methylotrophic bacteria, catalysing the oxidation of methanol to formaldehyde. In many methylotrophs, this is a well-characterised pyrroloquinoline quinone dependent enzyme consisting of two subunits, encoded by the genes mxaFI. A homolog of the large subunit MxaF is also present in most known methylotrophs, encoded by the gene xoxF. In several methylotrophs, this gene was found to be the only putative methanol dehydrogenase, but it is also present in several non-methylotrophs. This has led to a discussion over its potential role in methylotrophy and C1 cycling. This study aims to investigate the presence and diversity of the xoxF gene in the marine environment.