Publications

4367

Here we report the detection of Candidatus Rickettsia tarasevichiae from tick collected from human patient through DNA amplification. The tick was identified to be Haemaphysalis longicornis. We amplified and sequenced rickettsial citrate synthase gene (gltA), 190_kDa outer protein gene (ompA), and 120_ kDa outer protein gene (ompB). Sequencing results showed that gltA gene and ompA (GenBank accession No. KT899085, KT899079, respectively) shared 100% nucleotide sequence similarities with Candidatus R. tarasevichiae. In addition, ompB gene shared 96% nucleotide sequence similarity with R. canadensis. However, DNA extracted from patient serum showed 98% sequence similarity with R. japonica (AF123713.1). This result implies that H. longicornis ticks harbor both Candidatus R. tarasevichiae and R. japonica.

AbstractMembers of the order Rickettsiales are often found in association with ciliated protists. An interesting case is the bacterial endosymbiont “Candidatus Megaira”, which is phylogenetically closely related to the pathogen Rickettsia. “Candidatus Megaira” was first described as an intracellular bacterium in several ciliate species. Since then it has been found in association with diverse evolutionary distantly-related hosts, among them other unicellular eukaryotes, and also algae, and metazoa, such as cnidarians. We provide the characterization of several new strains of the type species “Candidatus Megaira polyxenophila”, and the multidisciplinary description of a novel species, “Candidatus Megaira venefica”, presenting peculiar features, which highlight the diversity and variability of these widespread bacterial endosymbionts. Screening of the 16S rRNA gene short amplicon database and phylogenetic analysis of 16S rRNA gene hypervariable regions revealed the presence of further hidden lineages, and provided hints on the possibility that these bacteria may be horizontally transmitted among aquatic protists and metazoa. The phylogenetic reconstruction supports the existence of at least five different separate species-level clades of “Candidatus Megaira”, and we designed a set of specific probes allowing easy recognition of the four major clades of the genus.

‘Candidatus Ornithobacterium hominis’ represents a new member of the Flavobacteriaceae detected in 16S rRNA gene surveys of people from South-East Asia, Africa and Australia. It frequently colonizes the infant nasopharynx at high proportional abundance, and we demonstrate its presence in 42 % of nasopharyngeal swabs from 12-month-old children in the Maela refugee camp in Thailand. The species, a Gram-negative bacillus, has not yet been cultured, but the cells can be identified in mixed samples by fluorescent hybridization. Here, we report seven genomes assembled from metagenomic data, two to improved draft standard. The genomes are approximately 1.9 Mb, sharing 62 % average amino acid identity with the only other member of the genus, the bird pathogen Ornithobacterium rhinotracheale . The draft genomes encode multiple antibiotic-resistance genes, competition factors, Flavobacterium johnsoniae -like gliding motility genes and a homologue of the Pasteurella multocida mitogenic toxin. Intra- and inter-host genome comparison suggests that colonization with this bacterium is both persistent and strain exclusive.