Analysis of diverse eukaryotes suggests the existence of an ancestral mitochondrial apparatus derived from the bacterial type II secretion system

The type 2 secretion system (T2SS) is present in some Gram-negative eubacteria and used to secrete proteins across the outer membrane. Here we report that certain representative heteroloboseans, jakobids, malawimonads and hemimastigotes unexpectedly possess homologues of core T2SS components. We show that at least some of them are present in mitochondria, and their behaviour in biochemical assays is consistent with the presence of a mitochondrial T2SS-derived system (miT2SS). We additionally identified 23 protein families co-occurring with miT2SS in eukaryotes. Seven of these proteins could be directly linked to the core miT2SS by functional data and/or sequence features, whereas others may represent different parts of a broader functional pathway, possibly also involving the peroxisome. Its distribution in eukaryotes and phylogenetic evidence together indicate that the miT2SS-centred pathway is an ancestral eukaryotic trait. Our findings thus have direct implications for the functional properties of the early mitochondrion

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. The family comprises two genera, Tropidoatractus and Palmarella, and five species, two of which are newly described herein. Tropidoatractidae are cosmopolitan Metopida with sparse somatic and oral ciliature, deep, cup-like buccal cavity, and hyaline cortex with interkinetal ridges. Moreover, all species occur in two morphotypes, slender and stout. They inhabit microoxic or anoxic freshwater, brackish, and marine sediments and possess anaerobic mitochondrion-related organelles and various prokaryotic symbionts. The discovery of Tropidoatractidae provides valuable information about the evolution of Armophorea and gives us insights to the diversity and ecological preferences of anaerobic ciliates in general

Morphologic and Molecular Characterization of Seven Species of the Remarkably Diverse and Widely Distributed Metopid Genus \u3cem\u3eUrostomides\u3c/em\u3e Jankowski, 1964 (Armophorea, Ciliophora)

The free-living ciliates of the order Metopida Jankowski, 1980 are pivotal playersin 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. In this report we provide morphologic and molecular characterization of seven taxa from the poorly-known resurrected genus Urostomides obtained in the course of broad geographic sampling. Foissner (2016) established the family Apometopidae to include Apometopus (a junior synonym of Urostomides) and Cirranter Jankowski, 1964. These two genera differ from all other metopid genera in having a four-rowed perizonal ciliary stripe, the only currently recognizable morphologic synapomorphy for the family. The members of Urostomides show remarkable morphologic diversity. The genus has a broad geographic distribution, occurring on six continents. Urostomides speciesform a strongly supported clade in phylogenetic analyses. Relationships within the genus itself are less clearly resolved. The diagnoses of Apometopidae and Urostomides are emended

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., Castula flexibilis sp. nov., and Longitaenia australis sp. nov. Based on morphologic features and the 18S rRNA gene phylogeny, we transfer two known species of Metopus to the new genus Castula, as C. fusca (Kahl, 1927) comb. nov. and C. setosa (Kahl, 1927) comb. nov.. and another known species is herein transferred to the new genus Longitaenia, as L. gibba (Kahl, 1927) comb. nov. Pileometopus is characterized by a turbinate body shape, a dorsal field of densely spaced dikinetids, a bipartite paroral membrane, and long caudal cilia. A distinctive morphologic feature of Castula species is long setae arising over the posterior third of the body (as opposed to a terminal tuft). Longitaenia spp. are characterized by an equatorial cytostome and long perizonal ciliary stripe relative to the cell length. Based on phylogenetic analyses of 18S rRNA gene sequences we identify and briefly discuss strongly supported clades and intraspecific genetic polymorphism within the order Metopida

Redescription and Molecular Phylogeny of the Type Species for Two Main Metopid Genera, \u3cem\u3eMetopus es\u3c/em\u3e (Müller, 1776) Lauterborn, 1916 and \u3cem\u3eBrachonella contorta\u3c/em\u3e (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. es and three strains of B. contorta were studied in detail, providing the first correlation of morphology, morphometrics, and 18S rRNA gene sequencing for both. We submitted 29 new 18S rRNA gene sequences to GenBank. Phylogenetic analyses yielded trees of similar topology. A strongly supported Metopus es clade is sister to the Brachonella contorta clade. Our analysis shows genus Metopus is not monophyletic. The monophyly of Brachonella cannot yet be determined due to lack of sequences for other species of this genus in molecular databases. Both species appear to have a global distribution. Metopus es was not found in Africa, probably reflecting low sampling effort. Strains of both species showed low 18S rRNA gene sequence divergence despite wide geographic separation

The Little-Known Freshwater Metopid Ciliate, \u3cem\u3eIdiometopus turbo\u3c/em\u3e (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. Metopus turbo Dragesco and Dragesco-Kernéis, 1986, from a West African pond, was more recently described. Although not explicitly described as endemic, Dragesco believed in some degree of endemism of sub-Saharan ciliates. Our discovery of M. turbo on Guam, Micronesia was unexpected. Metopus turbo was identified by live observation, protargol impregnation, and scanning electron microscopy, providing reasonable evidence of conspecificity when compared with the original description. Outstanding morphologic features include the stout shape and transversely situated bandform macronucleus. The morphology of Metopus turbo differs markedly from that of the Metopus/Brachonella cladeand is distant from Metopus es in phylogenetic analyses. The 18S rDNA sequence of the Guam M. turbo differs from that of M. es, type species of Metopus, by \u3e8% and shows distinct morphologic differences from the genus Atopospira to which it is sister. These facts suggest that transfer to a new genus, Idiometopus gen. nov. is indicated