Genomic Evidence for Two Pathways of Formaldehyde Oxidation and Denitrification Capabilities of the Species Paracoccus Methylovorus Sp. Nov.

Three strains (H4--D09T, S2--D11 and S9--F39) of a member of the genus Paracoccus attributed to a novel species were isolated from topsoil of temperate grasslands. The genome sequence of the type strain H4--D09T exhibited a complete set of genes required for denitrification as well as methylotrophy. The genome of H4--D09T included genes for two alternative pathways of formaldehyde oxidation. Besides the genes for the canonical glutathione (GSH)--dependent formaldehyde oxidation pathway, all genes for the tetrahydrofolate-formaldehyde oxidation pathway were identified. The strain has the potential to utilize methanol and/or methylamine as a single carbon source as evidenced by the presence of methanol dehydrogenase (mxaFI) and methylamine dehydrogenase (mau) genes. Apart from dissimilatory denitrification genes (narA, nirS, norBC and nosZ), genes for assimilatory nitrate (nasA) and nitrite reductases (nirBD) were also identified. The results of phylogenetic analysis based on 16S rRNA genes coupled with riboprinting revealed that all three strains represented the same species of genus Paracoccus. Core genome phylogeny of the type strain H4--D09T indicated that Paracoccus thiocyanatus and Paracoccus denitrificans are the closest phylogenetic neighbours. The average nucleotide index (ANI) and digital DNA-DNA hybridization (dDDH) with the closest phylogenetic neighbours revealed genetic differences at the species level, which were further substantiated by differences in several physiological characteristics. The major respiratory quinone is Q--10, and the predominant cellular fatty acids are C 18: 1.7c, C 19: 0cyclo.7c, and C 16:0, which correspond to those detected in other members of the genus. The polar lipid profile consists of a diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylcholine (PC), aminolipid (AL), glycolipid (GL) and an unidentified lipid (L). On the basis of our results, we concluded that the investigated isolates represent a novel species of the genus Paracoccus, for which the name Paracoccus methylovorus sp. nov. (type strain H4--D09T=LMG 31941T= DSM 111585T) is proposed.