Sequence analysis and comparison of 190 K surface antigen gene fragment of a new species of spotted fever group rickettsiae

A 533 bp long PCR product amplified from rickettsial strain HL-93 DNA with the primer pair Rr 190.70p and Pr 190.602n, designed from DNA sequence encoding 190 K protein antigen of R. rickettsii, was cloned into plasmid vector PGEM-T and sequenced. The primer-flanking region of the product, an open reading frame, was 491 bp long. The sequence of the product was compared with those of the corresponding regions of DNAs of R. rickettsii (strain R), R. japonica (strain VR1363) and R. conorii (strain Malish 7) which were reported earlier by other authors. The results showed that 23, 31 and 52 nucleotides in the compared sequence in strain HL-93 differed from those in R. japonica, R. rickettsii and R. conorii, respectively. The homologies of strain HL-93 with R. japonica, R. rickettsii and R. conorii were 95.6%, 94% and 90% in nucleotide, and 89%, 87% and 80% in putative amino acid sequences. We consider strain HL-93 as a new member of spotted fever group (SFG) rickettsiae on the basis of a high degree of homology and genetic divergence in the nuclcotide sequence of a part of the 190 K protein gene.