“CandidatusAnadelfobacter veles” and “CandidatusCyrtobacter comes,” Two NewRickettsialesSpecies Hosted by the Protist CiliateEuplotes harpa(Ciliophora, Spirotrichea)

Abstract

The order Rickettsiales (Alphaproteobacteria) is a well-known group containing obligate endocellular prokaryotes. The order encompasses three families (Rickettsiaceae, Anaplasmataceae, and Holosporaceae) and a fourth, family-level cluster, which includes only one candidate species, "Candidatus Midichloria mitochondrii," as well as several unnamed bacterial symbionts. The broad host range exhibited by the members of the "Candidatus Midichloria" clade suggests their eventual relevance for a better understanding of the evolution of symbiosis and host specificity of Rickettsiales. In this paper, two new bacteria belonging to the "Candidatus Midichloria" clade, hosted by two different strains of the ciliate protist Euplotes harpa, are described on the basis of ultrastructural observations, comparative 16S rRNA gene sequence analysis, and an estimation of the percentage of infection. Ultrastructure of these bacteria shows some unusual features: one has an electrondense cytoplasm, and the other one lacks a symbiosomal membrane. The latter was up to now considered an exclusive feature of bacteria belonging to the family Rickettsiaceae. 16S rRNA gene phylogenetic analysis unambiguously places the new bacteria in the "Candidatus Midichloria" clade, although their phylogenetic relationships with other members of the clade are not clearly resolved. This is the first report of a ciliate-borne bacterium belonging to the "Candidatus Midichloria" clade. On the basis of the data obtained, the two bacteria are proposed as two new candidate genera and species, "Candidatus Anadelfobacter veles" and "Candidatus Cyrtobacter comes."

“Candidatus Sonnebornia yantaiensis”, a member of candidate division OD1, as intracellular bacteria of the ciliated protist Paramecium bursaria (Ciliophora, Oligohymenophorea)

“…However, the bacterial symbiont's lack of an equivalent of the perialgal vacuole membrane suggests that it is digestion-resistant, much like some other bacteria in free-living amoebae [29] and ciliates [e.g. 10,18,19,64,67].…”

“…More recently, our knowledge of the diversity of bacteria associated with ciliates has increased significantly, primarily as a result of extensive molecular investigations of some commonly occurring species of the genera Paramecium and Euplotes. These studies have demonstrated that most bacterial symbionts belong to one of four classes of the phylum Proteobacteria, namely Alphaproteobacteria (including pathogenic Rickettsia) [2,8,9,18,19,21,22,51,59,60,62,64,67,69], Betaproteobacteria [58,63,66,68], Gammaproteobacteria [4,10,48,53] and Deltaproteobacteria [15]. Associations between ciliates and bacteria of other phyla seem to be infrequent, for example, Verrucomicrobia [42] and Firmicutes [54].…”

“Candidatus Hepatobacter penaei,” an Intracellular Pathogenic Enteric Bacterium in the Hepatopancreas of the Marine Shrimp Penaeus vannamei (Crustacea: Decapoda)

“…Recent nucleotide sequence additions from this order of bacteria to public databases refines the placement of the 16S rRNA sequence in the genera classified as "incertae sedis," with low support branching probability (64.76%) in the family Holosporaceae (Fig. 1A) (15)(16)(17)(18)(19). Both Holospora spp.…”

«candidatus Midichloria Mitochondrii»: A New Member of Order Rickettsiales, Endosymbiont of Ixodes Ricinus Tick

“…Бактерии группы MALOs (midichloria and like organisms), филогенетически близкие с «Candidatus M. mitochondrii», продемонстриро-вали связь с широким кругом хозяев: от члени-стоногих (клещи, блохи, клопы и жуки) до ин-фузорий, амеб, губок, рыб и различных живот-ных, включая человека [1,6,10,17,19,21,23,44]. При изучении последовательностей гена 16S рРНК группа MALOs образовала монофилети-ческую группу, структурированную на отдель-ные подгруппы (клады), которые могут пред-ставлять новые рода, и заняла позицию на уров-не описанных семейств из порядка Rickettsiales, что привело к предложению выделить новое семейство -«Candidatus Midichloriaceae» [23].…”

“…Применение молекулярно-биологических методов в последние десятилетия привело к описанию новых видов риккетсий, включая патогенные для человека виды [27], а также некультивируемых в лабораторных условиях микроорганизмов из порядка Rickettsiales [6,14,15,22,39,44], которые в соответствии с ре-комендациями ICSB (International Committee of Systematic Bacteriology) были классифици-рованы как «Candidatus sp.» [24]. Эндосимби-онт иксодовых клещей Ixodes ricinus «Candidatus Midichloria mitochondrii» требует особого вни-мания со стороны исследователей, так как яв-ляется единственной из известных в настоя-щее время бактерий, которая была обнаружена внутри митохондрий животных [4,34,36].…”