Diverse marine Vibrio species convert methylphosphonate to methane

Microbial degradation of methylphosphonate (MPn) is an important pathway contributing to the 'methane paradox' in the oxic ocean. Vibrio spp. are suggested to participate in this process. However, little is known about the molecular basis, phylogenetic breadth and catabolic efficiency of methane production in Vibrio species. Here, 18 Vibrionales strains known to be effective in MPn demethylation were obtained. The most effective strains, i.e., Vibrio gallaecicus HW2-07 and HW2-08, can convert 70%–80% of amended MPn into methane in 5 days. Estimations based on quantitative PCR determination indicated that Vibrio spp. were influential contributors to marine methane production. Genes flanking the common phn genes suggested a divergent gene arrangement and grouped the phn operons into nine types. This was consistent with the phylogeny of phnJ and phnL. The phn operons of cluster Ⅰ and Ⅱ were identified frequently in Vibrio isolates and were common in coastal seas and the open ocean. Addition of MPn increased expression of the phn genes, as well as an unexpected gene that encodes an acyltransferase (act), which frequently occurred in cluster Ⅰ–Ⅳ operons. This study provided experimental evidence and theoretical support for a further understanding that Vibrio spp. may play important roles in aerobic marine methane production.