Proposal of Sphingomonadaceae fam. nov., consisting of Sphingomonas Yabuuchi et al. 1990, Erythrobacter Shiba and Shimidu 1982, Erythromicrobium Yurkov et al. 1994, Porphyrobacter Fuerst et al. 1993, Zymomonas Kluyver and van Niel 1936, and Sandaracinobacter Yurkov et al. 1997, with the type genus Sphingomonas Yabuuchi et al. 1990.

Based on the results of phylogenetic analysis of the 16S rDNA sequences and the presence of N-2'-hydroxymyristoyl dihydrosphingosine 1-glucuronic acid (SGL-1) and 2-hydroxymyristic acid (non-hydroxymyristic acid in Zymomonas) in cellular lipids, a new family, Sphingomonadaceae, for Group 4 of the alpha-subclass of the class Proteobacteria is herein proposed and a description of the family is given. The family consists of six genera, Sphingomonas, Erythrobacter, Erythromicrobium, Porphyrobacter, Sandaracinobacter and Zymomonas. Thus, all the validly published and currently known genera in Group 4 of the alpha-subclass of Proteobacteria belong to Sphingomonadaceae fam. nov. Among them, type strains of two species, Porphyrobacter and Erythrobacter, Sandaracinobacter sibiricus and Sphingomonas ursincola, respectively, are facultatively photosynthetic due to bacteriochlorophyll (Bchl)-a. The type strains of two subspecies of Zymomonas mobilis are facultative anaerobes. The presence of SGL-1 together with the results of a phylogenetic analysis of the 16S rDNA sequences recommends a new criteria by which to define the new family Sphingomonadaceae. The type genus is Sphingomonas Yabuuchi et al. 1990.