Reclassification of the polyphyletic genus Prosthecomicrobium to form two novel genera, Vasilyevaea gen. nov. and Bauldia gen. nov. with four new combinations: Vasilyevaea enhydra comb. nov., Vasilyevaea mishustinii comb. nov., Bauldia consociata comb. nov. and Bauldia litoralis comb. nov

Abstract

Species of the genus Prosthecomicrobium are noted for their numerous cellular appendages or prosthecae that extend from the cells. This investigation confirms that the genus is polyphyletic based on an extensive analysis of the 16S rRNA gene sequences of several named species of the genus. The analyses indicate that some Prosthecomicrobium species are more closely related to non-prosthecate genera, including Devosia, Labrenzia, Blastochloris, Methylosinus, Mesorhizobium and Kaistia, than they are to other species of the genus Prosthecomicrobium. For this reason, two of the Prosthecomicrobium clades which are polyphyletic with the type species, Prosthecomicrobium pneumaticum, are renamed as new genera. The currently named species Prosthecomicrobium enhydrum, Prosthecomicrobium mishustinii, Prosthecomicrobium consociatum and Prosthecomicrobium litoralum are reclassified in two new genera, Vasilyevaea gen. nov. and Bauldia gen. nov. with four new combinations: Vasilyevaea enhydra comb. nov. (the type species) and Vasilyevaea mishustinii comb. nov., and Bauldia consociata comb. nov. and Bauldia litoralis comb. nov. (the type species). The type strain of Vasilyevaea enhydra is strain 9b(T) (=ATCC 23634(T) =VKM B-1376(T)). The type strain of the other species in this genus is Vasilyevaea mishustinii strain 17(T) (=VKM B-2499(T) =CCM 7569(T)). The type strain of Bauldia litoralis is strain 524-16(T) (= NCIB 2233(T) =ATCC 35022(T)). The type strain of the other species in this genus is Bauldia consociata strain 11(T) (=VKM B-2498(T) =CCM 7594(T)).

Fig. 1.

Maximum-likelihood tree based on 16S rRNA gene sequences showing the relationship of the Prosthecomicrobium strains (in bold) and the new genera within the class Alphaproteobacteria. The Escherichia coli 16S rRNA gene sequence was used as an outgroup to root the tree. Circles indicate consensus bootstrap values from maximum-likelihood, distance and maximum-parsimony analyses. Nodes supported at ≥75 % in the majority of analyses are indicated by filled circles. Nodes supported at 50–74 % in most analyses are indicated by open circles. Unsupported nodes (≤50 %) have no circle. Bar, 0.1 substitutions per site.