Phylogenetic analysis of mycoplasmas based on Hsp70 sequences: cloning of the dnaK (hsp70) gene region of Mycoplasma capricolum.

A 5.0-kb region containing the hsp70 (dnaK) gene was cloned from Mycoplasma capricolum and sequenced. In addition to the hsp70 gene, this sequence region also contained the complete sequences for the grpE and orfA genes and partial sequences for the clpB and dnaJ genes. The order of the above gene sequences in the cloned fragment was found to be clpB-orfA-grpE-hsp70-dnaJ, which is similar to the order seen in various other gram-positive groups of bacteria. The Hsp70 homologs from two mycoplasma species, Mycoplasma capricolum and Mycoplasma genitalium, contain a number of sequence signatures, including the absence of a large insert in the N-terminal quadrant, that are characteristics of the homologs from gram-positive bacteria and archaebacteria. A detailed phylogenetic analysis based on Hsp70 sequences was also performed. In neighbor-joining and parsimony trees based on Hsp70 sequences, both mycoplasma species branched with the low-G + C-content gram-positive group of bacteria (e.g., Lactobacillus and Erysipelothrix species) in 87% and 96% of the bootstrap replicates, respectively, indicating their close evolutionary relationship to this group. The phylogenetic trees based on Hsp70 sequences show a polyphyletic branching of archaebacteria with the gram-postive species, which is statistically strongly favored.