Dissection of the genus Methylibium: reclassification of Methylibium fulvum as Rhizobacter fulvus comb. nov., Methylibium aquaticum as Piscinibacter aquaticus gen. nov., comb. nov. and Methylibium subsaxonicum as Rivibacter subsaxonicus gen. nov., comb. nov. and emended descriptions of the genera Rhizobacter and Methylibium.

16S rRNA gene sequenced-based phylogeny indicates that Rhizobacter dauci ATCC 43778(T) branches within the radiation of Methylibium type strains. A comparative chemotaxonomic study including fatty acid methyl esters, polar lipids and polyamines reveals significant differences that, in combination with the topology of phylogenetic trees, support a dissection of the genus Methylibium. The proposals of this study include the transfer of Methylibium fulvum to the genus Rhizobacter as Rhizobacter fulvus comb. nov. (type strain Gsoil 322(T) =KCTC 12591(T) =DSM 19916(T)) and the reclassification of Methylibium aquaticum as Piscinibacter aquaticus gen. nov., comb. nov. (the type strain of Piscinibacter aquaticus is IMCC1728(T) =KCCM 42364(T) =NBRC 102349(T) =DSM 19915(T)) and of Methylibium subsaxonicum as Rivibacter subsaxonicus gen. nov., comb. nov. (the type strain of Rivibacter subsaxonicus is BF49(T) =DSM 19570(T) =CIP 109700(T)). As a consequence of these reclassifications, emended descriptions of the genera Methylibium and Rhizobacter are provided.