Journal of Eukaryotic Microbiology最新文献

Mitochondria of eukaryotic cells are direct descendants of an endosymbiotic bacterium related to Alphaproteobacteria. These organelles retain their own genomes, which are highly reduced and divergent when compared to those of their bacterial relatives. To better understand the trajectory of mitochondrial genome evolution from the last eukaryotic common ancestor (LECA) to extant species, mitochondrial genome sequences from phylogenetically diverse lineages of eukaryotes—particularly protists—are essential. For this reason, we focused on the mitochondrial genomes of Ancyromonadida, an independent and understudied protist lineage in the eukaryote tree of life. Here we report the mitochondrial genomes from three Ancyromonadida: Ancyromonas sigmoides, Nutomonas longa, and Fabomonas tropica. Our analyses reveal that these mitochondrial genomes are circularly mapping molecules with inverted repeats that carry genes. This inverted repeat structure has been observed in other mitochondrial genomes but is patchily distributed over the tree of eukaryotes. Ancyromonad mitochondrial genomes possess several protein-coding genes, which have not been detected from any other mitochondrial genomes of eukaryotes sequenced to date, thereby extending the known mitochondrial gene repertoire of ancestral eukaryotes, including LECA. These findings significantly expand our understanding of mitochondrial genome diversity across eukaryotes, shedding light on the early phases of mitochondrial genome evolution.

The genera Paramoeba and Neoparamoeba, within the family Paramoebidae (order Dactylopodida), are distinguished by their dactylopodial pseudopodia and the presence of an intracellular eukaryotic symbiont, the Perkinsela-like organism (PLO). Taxonomic classification within these genera has been challenging due to overlapping morphological traits and close phylogenetic relationships. They are marine, with some playing significant roles as parasites. Notably, they have been implicated in sea urchin mass mortality events and are known causative agents of Amoebic Gill Disease (AGD) in fish. Despite their ecological and economic importance, many aspects of their diversity, biology, evolution, and host interactions remain poorly understood. In this study, we describe a novel amoeba species, Paramoeba daytoni n. sp., isolated from Daytona Beach, Florida. Morphological and molecular analyses confirm its placement within the Paramoeba clade, closely related to P. eilhardi, P. karteshi, and P. aparasomata. Phylogenetic assessments using 18S rDNA (18S) and Cytochrome c Oxidase I (COI) markers demonstrate the limitations of the 18S gene for species delineation, highlighting COI as a more reliable genetic marker for this group. Additionally, observations on PLO morphology, movement, and microtubule association provide insights into the endosymbiotic relationship, reinforcing the need for further research into this unique eukaryote-eukaryote symbiosis.

Photosymbioses, the symbiotic relationships between microalgae and non-photosynthetic eukaryotes, are sporadically found in many eukaryotic lineages. Only a few taxa, such as cnidarians and ciliates hosting algal endosymbionts, have been actively studied, which has hindered understanding the universal mechanisms of photosymbiosis establishment. In Amoebozoa, few species are reported as photosymbiotic, and how the photosymbioses are established is still unclear. To investigate the extent to which one of the photosymbiotic amoebae, Mayorella viridis, depends on their symbionts, the amoebae were treated with reagents known to induce the collapsing of photosymbioses in other species. We succeeded in removing algal symbionts from the hosts with 2-amino-3-chloro-1,4-naphthoquinone. While the apo-symbiotic amoebae grew to the same extent as the symbiotic state when they fed on prey, their survival rates were lower than those of the symbiotic ones during starvation, suggesting that the impact of the photosymbiosis on fitness is condition-dependent. Furthermore, we showed that the photosymbiotic state was reversible by feeding two strains of the green alga Chlorella to the apo-symbiotic amoebae. The efficiencies of ingesting algal cells significantly differed between algal strains. These results suggest that the photosymbiotic relationship in the amoeba is facultative and that different algal strains have discrete symbiotic abilities to the amoeba.

Most excavates, a paraphyletic assemblage of flagellates, typically present an active vaned flagellum that drives a feeding current through a ventral groove for predation. However, some have “atypical” morphologies. Here, we describe the foraging mechanisms in heteroloboseid flagellates (Discoba) that have a groove but lack the seemingly crucial vane. The percolomonads barbeliid AE-1 and Percolomonas doradorae form a functional vane with four adjacent flagella undulating with lateral asymmetry, creating an erratic flow that rapidly “sucks” water into the groove and expels it on the other side. This flow attenuates rapidly away from the cell, consistent with the flagellar pump acting as an instantaneous point sink. Conversely, Pharyngomonas kirbyi generates a continuous flow through the groove with two asynchronously moving posterior flagella. Despite the unexplained fluid dynamics, this flow has a further reach, consistent with describing the flagellar pump as a point force (stokeslet). While the volumetric flow rate through the groove—a measure of the maximum potential clearance rate—of the two percolomonads is similar to clearance rates estimated for other phagotrophic flagellates, it is an order of magnitude lower for Ph. kirbyi, which may afford lower rates due to high prey concentration in its hypersaline environment.

An autotrophic unarmored dinoflagellate species with haptophyte-derived plastids, Kapelodiniopsis flava n. g., n. sp., was described as a sister taxon of Kapelodinium vestifici, which was formerly well characterized by its low-positioned cingulum and heterotrophic nature. The isolates from several Japanese coastal locations were observed using light microscopy, scanning and transmission electron microscopy, and their phylogeny was inferred from nuclear-encoded rRNA genes and multiple plastid-encoded genes. To date of this publication, a representative culture of Ks. flava has grown autotrophically for 98 months in the absence of prey or organic matter. This dinoflagellate lacked nonplastid haptophyte cell components (e.g. nucleus or mitochondria). In the host dinoflagellate phylogeny, Ks. flava was distantly related to the other two dinoflagellate lineages known to be associated with haptophyte-derived plastids, thus representing the third of such lineage. Plastid origins differed among Ks. flava strains (>99.8% 18S rRNA gene identity), with plastids being derived from at least three haptophytes and an especially strong genetic similarity to two distantly related extant haptophytes (>99.9% 16S rRNA gene identity). This indicates that Ks. flava recently integrated plastids from multiple haptophyte lineages to an extent that allows the host to replicate the plastids without other haptophyte components.

Newly discovered hypotrich ciliates with evolutionary innovations are challenging to the established systematics and greater interest. Based on living morphology, infraciliature, and SSU rDNA, two bakuellid taxa—including a new species and a new subspecies—collected from subtropical soil environments in eastern China were investigated in the present study. Holostichides (Extraholostichides) eastensis ningboensis n. subsp. is characterized as follows: size in vivo 150–230 × 45–60 μm; cortical granules green and spherical; 3–5 small cirri arranged longitudinally posteriorly to middle frontal cirrus; row of 19–24 frontoterminal cirri exceeding half of the body length; 4–6 caudal cirri. Holostichides (Extraholostichides) muscus n. sp. is defined as follows: size in vivo 140–175 × 40–65 μm; cortical granules green and spherical; one or two small cirri posteriorly to the middle frontal cirrus; row of 3–6 frontoterminal cirri right of the midventral complex; three or four caudal cirri. Phylogenetic analyses based on SSU rDNA sequences revealed the systematic positions of these two new taxa and supported their validity as distinct subspecies and species, respectively.

Ancyromonadida is a taxon of small heterotrophic flagellates occupying an unresolved but deep-branching position in the eukaryotic tree of life, thus suspected to be important to studies of early eukaryotic evolutionary relationships and the characteristics of the last eukaryotic common ancestor. Sampling and cultivation of the full diversity of ancyromonad species are therefore areas of considerable interest. Ancyromonas melba is a species originally described from hypersaline material for which no monoprotistan culture or molecular data have been available, but whose distinct morphology suggests it may represent a new major lineage within Ancyromonadida. We report the first cultivation of this morphospecies in hypersaline media, with characterization including scanning electron microscopy and small subunit rRNA gene sequencing. Distinguishing morphological features include the predominantly ventral placement of the ventral groove, the approximately equal thickness of the anterior and posterior flagella, and the relatively long anterior flagellum. Phylogenetic analysis shows that the isolate does not branch within Ancyromonas or any other currently described genus of Ancyromonadida, but represents a novel genus-level lineage, the position of which within ancyromonads could not be robustly inferred. We therefore propose a new genus for this species and rename it Divimonas melba n. gen., n. comb.