Identification of a Ribosomal Protein RpsB as a Surface-Exposed Protein and Adhesin of Rickettsia heilongjiangensis

Rickettsia heilongjiangensis is an obligate intracellular bacterium that is responsible for far-eastern spotted fever. Surface-exposed proteins (SEPs) play important roles in its pathogenesis. Previous work identified a ribosomal protein RpsB as an SEP by biotin-avidin affinity, a seroreactive antigen, and a diagnostic candidate protein, indicating that it might play an important role in the pathogenesis of rickettsiae. However, in the absence of other evidence, its subcellular location of being surface-exposed was puzzling because ribosomal proteins are located in the cytoplasm. In the present study, the subcellular location of RpsB was analyzed with bioinformatics tools coupled with immunoelectron microscopy. The adhesion ability of RpsB was evaluated by protein microarray and cellular ELISA. Consequently, different bioinformatics tools gave different location predication results. Thus, RpsB was found in the cytoplasma and inner and outer membranes of R. heilongjiangensis by transmission electron microscopy. Protein microarray and cellular ELISA showed that RpsB binds to the host cell surface and its adhesion ability was even stronger than the known adhesin Adr1. In conclusion, RpsB was visually and directly shown for the time to be an SEP of rickettsiae and might be an important ligand and adhesin of rickettsiae. Its roles in pathogenesis warrant further study.

Genome Sequence of “Candidatus Rickettsia colombianensi,” a Novel Tick-Associated Bacterium Distributed in Colombia

This is the first report of the genome sequence of “Candidatus Rickettsia colombianensi” strain Adcor 2, deposited in DDBJ/ENA/GenBank under the accession number RAQN00000000. The draft genome showed 36.01% similarity with that of Rickettsia monacensis strain IrR/Munich (NCBI accession number LN794217), 37.81% similarity with that of Rickettsia heilongjiangensis 054 (NCBI accession number CP002912), and 43.88% similarity with that of Rickettsia tamurae AT-1 (NCBI accession number CCMG01000001).

IXODES TICKS AS VECTORS OF TICK-BORNE INFECTIONS IN THE SOUTH OF PRIMORSKY KRAI (KHASANSKY DISTRICT)

The Khasan district, located in the south of the Primorsky Krai, borders with the Democratic People’s Republic of Korea (DPRK) and the People’s Republic of China (PRC). This determines the special importance in terms of epizootological observations of the causative agents of vector-borne tick infections. To date, such studies have not been carried out in the Khasan district.Aims: to show infections of ixodid ticks in the south of Primorsky Krai (in the Khasansky District), causative agents of viral and bacterial tick-borne infections.Materials and methods. During the period of 2017, 387 specimens of ixodid ticks were collected from the vegetation. The study of collected ticks was carried out using the real-time polymerase chain reaction method.Results. RNA of the TBE virus was detected in 1.1 %, Borrelia burgdorferi sensu lato DNA in 12.5 %, Borrelia miyamotoi DNA in 0.6 %, Anaplasma phagocytophillum DNA in 4 %, Ehrlichia chaffeensis / Ehrlichia muris DNA in 1.7 %. In 8 %, rickettsia DNA was detected, of which Rickettsia heilongjiangensis in 12 cases. Seven cases of mixed infection of various species of ticks with two pathogens were detected.Conclusions. The data obtained suggest that the pathogens of infections transmitted by ixodid ticks can circulate not only throughout the border area of the south of the Primorsky Krai (Khasansky District) but also in the adjacent territories of the PRC and DPRK.