Determination of Coxiella burnetii rpoB sequence and its use for phylogenetic analysis

The nucleotide sequence of the rpoB, encoding the beta-subunit of RNA polymerase of the obligate intracellular bacterium Coxiella burnetii, was determined using a polymerase chain reaction amplification and direct sequencing methodology. Comparison between C. burnetii and other eubacterial rpoB sequences indicated sequence similarity ranging from 53.6% to 67.6%. Coxiella burnetii rpoB consists of 4128 base pairs with a 45.3% GC content encoding 1375 amino acids with a calculated molecular mass of 153.67 kDa. Comparison of 512 bases of the rpoB variable region I, from eight C. burnetii strains isolated from various sources, revealed fewer than four base differences, although the distribution of these did not correlate with previously determined genotypic groupings with the species. Phylogenetic analysis of C. burnetii based on comparison of its rpoB sequence with sequences available for other bacteria is consistent with those previously derived from 16S rRNA gene sequence, and indicate that C. burnetii belongs to the gamma-group of Proteobacteria. Furthermore, phylogeny inferred from comparison of RpoB, or homologous sequences including Archae, Bacteria and Eukarya, concurred with these results.