Methanogenic symbionts of anaerobic ciliates are host and habitat specific.

The association between anaerobic ciliates and methanogenic archaea has been recognized for over a century. Nevertheless, knowledge of these associations is limited to a few ciliate species, and so the identification of patterns of host-symbiont specificity has been largely speculative. In this study, we integrated microscopy and genetic identification to survey the methanogenic symbionts of 32 free-living anaerobic ciliate species, mainly from the order Metopida.

Divergent marine anaerobic ciliates harbor closely related Methanocorpusculum endosymbionts.

Ciliates are a diverse group of protists known for their ability to establish various partnerships and thrive in a wide variety of oxygen-depleted environments. Most anaerobic ciliates harbor methanogens, one of the few known archaea living intracellularly. These methanogens increase the metabolic efficiency of host fermentation via syntrophic use of host end-product in methanogenesis.

Single cell transcriptomics reveals UAR codon reassignment in Palmarella salina (Metopida, Armophorea) and confirms Armophorida belongs to APM clade.

Anaerobes have emerged in several major lineages of ciliates, but the number of independent transitions to anaerobiosis among ciliates is unknown. The APM clade (Armophorea, Muranotrichea, Parablepharismea) represents the largest clade of obligate anaerobes among ciliates and contains free-living marine and freshwater representatives as well as gut endobionts of animals. The evolution of APM group has only recently started getting attention, and our knowledge on its phylogeny and genetics is still limited to a fraction of taxa.

Morphology, morphogenesis, and molecular characterization of Castula specialis sp. nov. (Ciliophora, Armophorea, Metopida).

The morphology, morphogenesis, and molecular phylogeny of a new metopid ciliate, Castula specialis sp. nov., comprising three strains from geographically distant (China, Mexico, Czech Republic) anoxic freshwater habitats, were studied based on microscopic observation of live and protargol-stained specimens as well as SSU rRNA gene sequence data.

Morphology and phylogenetic position of three anaerobic ciliates from the classes Odontostomatea and Muranotrichea (Ciliophora).

The diversity of the classes Odontostomatea and Muranotrichea, which contain solely obligate anaerobes, is poorly understood. We studied two populations of Mylestoma sp., one of Saprodinium dentatum (Odontostomatea), two of Muranothrix felix sp.

Diversity and Phylogenetic Position of Bothrostoma Stokes, 1887 (Ciliophora: Metopida), with Description of Four New Species.

Bothrostoma is a genus of anaerobic ciliates in family Metopidae comprising four species, all described based solely on the morphology of living and fixed cells. Unlike other metopids, cells of Bothrostoma are not twisted anteriorly, have a flattened preoral dome, a very prominent sail-like paroral membrane, and an adoral zone of distinctive, very narrow, curved membranelles confined to a wide, non-spiraling peristome on the ventral side. We examined 20 populations of Bothrostoma from hypoxic freshwater sediments.

Anaerobic ciliates as a model group for studying symbioses in oxygen-depleted environments.

Anaerobiosis has independently evolved in multiple lineages of ciliates, allowing them to colonize a variety of anoxic and oxygen-depleted habitats. Anaerobic ciliates commonly form symbiotic relationships with various prokaryotes, including methanogenic archaea and members of several bacterial groups. The hypothesized functions of these ecto- and endosymbionts include the symbiont utilizing the ciliate's fermentative end products to increase the host's anaerobic metabolic efficiency, or the symbiont directly providing the host with energy by denitrification or photosynthesis.

Description of Three New Genera of Metopidae (Metopida, Ciliophora): Pileometopus gen. nov., Castula gen. nov., and Longitaenia gen. nov., with Notes on the Phylogeny and Cryptic Diversity of Metopid Ciliates.

We report the discovery of three new species of freshwater metopid ciliates, Pileometopus lynni gen. et sp. nov.

Genomics of New Ciliate Lineages Provides Insight into the Evolution of Obligate Anaerobiosis.

Oxygen plays a crucial role in energetic metabolism of most eukaryotes. Yet adaptations to low-oxygen concentrations leading to anaerobiosis have independently arisen in many eukaryotic lineages, resulting in a broad spectrum of reduced and modified mitochondrion-related organelles (MROs). In this study, we present the discovery of two new class-level lineages of free-living marine anaerobic ciliates, Muranotrichea, cl.

Morphologic and molecular characterization of Brachonella pulchra (Kahl, 1927) comb. nov. (Armophorea, Ciliophora) with comments on cyst structure and formation.

In this article we provide morphologic and morphometric data based on in vivo observation, protargol impregnation, scanning electron microscopy and an 18S rRNA gene sequence for another member of the genus Brachonella, Brachonella pulchra comb. nov. (basionym: Metopus pulcher Kahl, 1927).

The Little-known Freshwater Metopid Ciliate, Idiometopus turbo (Dragesco and Dragesco-Kernéis, 1986) nov. gen., nov. comb., Originally Discovered in Africa, Found on the Micronesian Island of Guam.

Class Armophorea Lynn, 2004 includes two orders of mainly free-living anaerobic ciliates, Armophorida Jankowski, 1980 and Metopida Jankowski, 1980 and, a third, the exclusively endosymbiotic Clevelandellida. Kahl described the majority of free-living metopid species early in the 20th century. Excepting Jankowski in the 1960's, little further interest was shown in this group.

Tropidoatractidae fam. nov., a Deep Branching Lineage of Metopida (Armophorea, Ciliophora) Found in Diverse Habitats and Possessing Prokaryotic Symbionts.

We report a discovery of a novel family of anaerobic ciliates, Tropidoatractidae fam. nov. Phylogenetic analyses based on the 18S rRNA gene show that the family Tropidoatractidae corresponds to the previously reported clade of environmental sequences closely related to the lineage consisting of orders Metopida and Clevelandellida.

Morphologic and molecular characterization of seven species of the remarkably diverse and widely distributed metopid genus Urostomides Jankowski, 1964 (Armophorea, Ciliophora).

The free-living ciliates of the order Metopida Jankowski, 1980 are pivotal players in the microbial food web of the sulfuretum, acting as hosts to prokaryotic endo- and ectosymbionts. They are also of interest in the study of the function and evolution of their mitochondrion-related organelle, the hydrogenosome. The taxonomy and phylogeny of this group remains confused, due, in large part, to the fact that most of its taxa have not been characterized by modern methods including molecular sequencing.

Redescription and molecular phylogeny of the type species for two main metopid genera, Metopus es (Müller, 1776) Lauterborn, 1916 and Brachonella contorta (Levander, 1894) Jankowski, 1964 (Metopida, Ciliophora), based on broad geographic sampling.

Metopid ciliates occupy terrestrial, freshwater, and marine habitats worldwide, playing important roles as predominant consumers of bacteria, flagellates, algae, and diatoms in hypoxic environments. Metopus and Brachonella are the most species-rich metopid genera, however most of their species have not been studied by modern methods Here, we report the morphologic, morphometric and molecular characterization, and phylogeny of Metopus es and Brachonella contorta, both types of their respective genera, collected in a broad global sampling effort. Five strains of M.