Whole genome sequence and comparative genomic analysis of novel Rickettsia koreansis strain CNH17-7 isolated from...

To determine the genomic feature of novel spotted fever-causing Rickettsia koreansis strain CNH17-7, which is different from R. japonica that is a causative agent for Japanese spotted fever (JSF), and to perform its comparative genomic analysis.

Whole genome sequencing (WGS) was performed on R. koreansis strain CNH17-7 by using the Illumina Miseq system. After WGS, assembly and annotation were done by SPAdes. Then, its genomic features were compared with 19 different Rickettsia species. Based on the average nucleotide identity (ANI) value, an unweighted pair group method with an arithmetic mean (UPGMA) dendrogram was generated. Following the dendrogram analysis, pan-and core-genome analysis was performed. Then additional comparative analyses with two genetically closest Rickettsia species were conducted based on gene repertoire.

R. koreansis strain CNH17-7 has a chromosome consisting of 1,392,633 bp with GC content of 32.4%. The ANI-derived UPGMA showed that R. koreansis strain CNH17-7 is genetically close to R. japonica YH and R. heilongjiangensis 054 but is distinctively differentiated. The ANI value of R. koreansis strain CNH17-7 to R. japonica YH and R. heilongjiangensis 054 are 98.14% and 98.04% respectively, indicating R. koreansis strain CNH17-7 is sufficient to be classified as a new species. Other than ANI, R. koreansis strain CNH17-7 also contains novel CDS and its COG functional category proportion which is distinct compared to R. japonica YH and R. heilongjiangensis 054.

We have revealed genomic features of the novel R. koreansis strain CNH17-7. Hence, we propose R. koreansis strain CNH17-7 as new Rickettsia species.