Determination of the systematic position of the genus Asticcacaulis Poindexter by a polyphasic analysis

The genus Asticcacaulis, to date, comprises two species of unicellular, sta lked bacteria, developing a stalk at a site which is not coincidental with the centre bacteria, developing a stalk at a site which is not coincidental with the cent of the pole of the cell. Multiplication is similar to that d emonstrated by the prosthecate species of the genera Caulobacter, Brevundim onas and Maricaulis. A polyphasic approach, comprising 16S rRNA gene sequen cing, lipid analysis and NaCl tolerance characterizations, was used to clar ify the taxonomy of the two Asticcacaulis species. From the analysis of the 16S rRNA gene sequences, a close phylogenetic relationship between the spe cies that comprise the genera Asticcacaulis, Caulobacter and Brevundimonas could be deduced wherein the three genera form three distinct branches. The individual genera could also be discerned by different characteristic pola r lipids. The species of Asticcacaulis differed from species of Caulobacter and Brevundimonas by the lack of 1,2-diacyl-3-O-[6'-phosphatidyl-alpha -D- glucopyranosyl]glycerol. They also did not contain 1,2-di-O-acyl-3-O-[D-glu copyranosyl-(1 --> 4)-alpha -D-glucuronopyranosyl]-glycerol, which is found in most Brevundimonas species hut not in strains of the genus Caulobacter. The morphological differences seen between the two species Asticcacaulis e xcentricus and Asticcacaulis biprosthecium are mirrored by the observed 16S rDNA sequence similarity value of 95.3%, which is relatively low compared to the interspecies similarity values observed within the genera Brevundimo nas or Caulobacter.