Abstract
Holospora-like bacteria (HLB) are obligate intracellular Alphaproteobacteria, inhabiting nuclei of Paramecium and other ciliates such as “Candidatus Hafkinia” is in Frontonia. The HLB clade is comprised of four genera, Holospora, Preeria, “Candidatus Gortzia”, and “Candidatus Hafkinia”. These bacteria have a peculiar life cycle with two morphological forms and some degree of specificity to the host species and the type of nucleus they inhabit. Here we describe a novel species of HLB—“Candidatus Gortzia yakutica” sp. nov.—a symbiont from the macronucleus of Paramecium putrinum, the first described HLB for this Paramecium species. The new endosymbiont shows morphological similarities with other HLB. The phylogenetic analysis of the SSU rRNA gene places it into the “Candidatus Gortzia” clade.
Highlights
Paramecium ciliates (Oligohymenophorea, Ciliophora, Alveolata) host diverse intracellular symbionts, among which the best studied are Holospora-like bacteria (HLB), obligate intranuclear bacteria of family Holosporaceae, order Holosporales, class Alphaproteobacteria [1,2,3,4]
HLB have a set of interesting features, such as a complex life cycle involving two morphological stages, infectious and reproductive, and infectious forms (IFs) which are unusually large for bacterial cells
A small number of IFs could be found in the cytoplasm of the host cell (Figure 2), suggesting that there might be an intermediate state before the symbiont release into the environment
Summary
Paramecium ciliates (Oligohymenophorea, Ciliophora, Alveolata) host diverse intracellular symbionts, among which the best studied are Holospora-like bacteria (HLB), obligate intranuclear bacteria of family Holosporaceae, order Holosporales, class Alphaproteobacteria [1,2,3,4]. HLB have a set of interesting features, such as a complex life cycle involving two morphological stages, infectious and reproductive, and infectious forms (IFs) which are unusually large for bacterial cells (up to 20 μm long). HLB species can distinguish between two types of host nuclei, macronucleus (Ma) and micronucleus (Mi) [2]. These features were traditionally used to assign bacteria to genus Holospora before any molecular information was available. Until the emergence of sequencing methods, all bacteria with the described morphological and physiological features were considered Holospora species and classified by their host specificity, localization in the host cell, size and shape of IFs and RFs, and the ability to trigger
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