Contractile Vacuole Research Articles

Establishing the role of the mitochondrial voltage-dependent anion channel (VDAC) in Trypanosoma cruzi.

The protozoan Trypanosoma cruzi is the causative agent of Chagas Disease, a neglected tropical disease that affects millions globally. As it transitions from insect vector to human host, T. cruzi faces homeostatic challenges, including oxidative stress, fluctuations in osmolarity, and nutrient availability. Ion channels regulate the parasite's ability to respond to environmental stressors. Our group has previously identified a mechanosensitive channel located in the contractile vacuole that, when knocked out, leads to reduced infectivity, abnormal morphology, and impaired motility. Transcriptomic analysis showed that Voltage-Dependent Anion Channel (VDAC) was significantly downregulated in the knockouts, suggesting a functional link between the two proteins. VDAC is a highly expressed outer mitochondrial membrane protein that, in other eukaryotes, regulates cell death, mitochondrial dynamics and metabolism. In protozoans, VDAC has been shown to share similar functions, with additional roles in tRNA and protein import. However, the function of VDAC in T. cruzi remains uncharacterized. The genome of T. cruzi contains five copies of VDAC sharing 99% homology. Four of them are organized in tandem, suggesting a gene expansion event as their most probable origin. To elucidate the function of this channel in the parasites, we targeted a conserved region using CRISPR/Cas9 strategies to generate a VDAC-deficient cell line. The mutant strain exhibited abnormal morphology and significant growth defects relative to the wild type, suggesting that VDAC is critical for parasite replication. Fluorometric analysis indicates that VDAC downregulation results in mitochondrial depolarization and reduced calcium uptake supporting its role in maintenance of mitochondrial functions.

Re-discovery and novel contributions to morphology and multigene phylogeny of Protospirella mazurica (Raabe, 1968) Aescht, 2001 (Ciliophora: Pleuronematida), an obligate symbiont of the river nerite Theodoxus fluviatilis Linnaeus, 1758 (Mollusca: Gastropoda)

Although the river nerite Theodoxus fluviatilis (Gastropoda: Neritimorpha) has an exceptionally broad geographical and ecological distribution, it carries only four ciliate species: Hypocomella quatuor, Protospirella mazurica, Scyphidia sp., and Trichodina baltica. After more than a half-century gap, we re-discovered P. mazurica in a Danubian population of T. fluviatilis (haplotypes F31 and F34) and characterized it using an integrative morpho-molecular approach. Protospirella mazurica is distinguished by (i) a small, elongate-ellipsoidal to ovoidal body, (ii) a broadly ellipsoidal macronucleus accompanied by a single globular micronucleus, (iii) a subterminal contractile vacuole, (iv) about 24 somatic kineties, (v) thigmotactic ciliature composed of about 10 kineties shortened posteriorly to form a parenthetical system, and (vi) a long inverted J-shaped paroral membrane associated with three unequally long membranelles. According to the present phylogenetic analyses of two mitochondrial and three nuclear markers, P. mazurica robustly clusters within the order Pleuronematida (Oligohymenophorea: Scuticociliatia) along with other symbiotic members of the families Hemispeiridae and Thigmophryidae as well as free-living representatives of the paraphyletic family Cyclidiidae. In light of the present phylogenetic analyses, we consider the family Ancistridae to be a junior synonym of the family Hemispeiridae, which collates 14 genera in our classification framework.

Endosomal vesicle fusion machinery is involved with the contractile vacuole in Dictyostelium discoideum.

Contractile vacuoles (CVs) share common characteristics, such as a requirement for RAB11 and high levels of V-ATPase. These commonalities suggest a conserved evolutionary origin for the CVs with implications for understanding of the last common ancestor of eukaryotes and eukaryotic diversification more broadly. A taxonomically broader sampling of CV associated machinery is required to address this question further. We used a transcriptomics-based approach to identify CV associated gene products in Dictyostelium discoideum. This approach was first validated by assessing a set of known CV associated gene products, which were significantly upregulated following hypo-osmotic exposure. Moreover, endosomal and vacuolar gene products were enriched in the upregulated gene set. An upregulated SNARE protein (NPSN) was predominantly plasma membrane localised and enriched in the vicinity of contractile vacuoles, supporting its transcriptomic association with this organelle. We therefore confirm that transcriptomic approaches can identify known and novel players in CV function, in our case emphasizing the role of endosomal vesicle fusion machinery in the D. discoideum CV and facilitating future work to address questions regarding the deep evolution of eukaryotic organelles.

Taxonomy and phylogeny of Pseudovorticella ciliates (Ciliophora, Peritrichia): Two new and one rare species from the coastal waters of China

Peritrich ciliates are a species-rich group of sessile unicellular eukaryotes, which can be found in various aquatic habitats from all over the world. It is well accepted that there are still many ciliates to be uncovered. During a survey on ciliate biodiversity in the coastal waters of China, three solitary peritrich species were identified as members of the genus Pseudovorticella Foissner & Schiffmann, 1975, including two new species and a rare one. Pseudovorticella zhejiangensis sp. n. differs from its congeners mainly by having a conical-shaped zooid, conspicuous pellicular blisters, one ventral and one dorsal contractile vacuoles, and an infundibular polykinety 3 with three rows of nearly equal length but different beginning positions. Pseudovorticella dalianensis sp. n. can be defined mainly by an obovoid-shaped zooid, one ventral contractile vacuole, and a three-rowed infundibular polykinety 3 with the middle row being the longest. The rare species, Pseudovorticella verrucosa (Dons, 1915) Sun et al., 2009, was redescribed. The small subunit (SSU) rDNA sequences of these three species were sequenced for the first time, the phylogeny of Pseudovorticella species was analyzed, and the results verified the non-monophyly of this genus. This study demonstrates that the morphologic and gene barcoding data are the optimum combination to disclose the biodiversity of ciliates.

Integrative Studies on Three Epibiotic Epistylis Species (Protozoa, Ciliophora, Peritrichia) in Lake Weishan Wetland, Northern China, Including the Establishment of a New Species

Three epibiotic Epistylis species, i.e., Epistylis weishanensis sp. nov., Epistylis daphniae Fauré-Fremiet, 1905, and Epistylis pygmaeum (Ehrenberg, 1838) Foissner et al., 1999, were investigated based on their living morphology, infraciliature, and small subunit (SSU) rDNA sequence data. Epistylis weishanensis sp. nov. is characterized by its double-layered peristomial lip, contractile vacuole located on the dorsal wall of the infundibulum, infundibular polykinety 3 (P3) composed of three equal-length rows that terminate above infundibular polykinety 1 (P1), 50-62 silverlines between the peristome and the trochal band, and about 30 silverlines between the trochal band and the scopula. Based on previous and newly obtained data for E. daphniae and E. pygmaeum, improved diagnoses and redescriptions are provided including, for the first time, data on their infraciliature. Phylogenetic analyses reveal that all three species do not group within the major clade of Epistylis, supporting the assertion that the genus Epistylis should be an assemblage of morphospecies and therefore needs to be revised.

The old and the new about the contractile vacuole of Trypanosoma cruzi.

Osmoregulation is a conserved cellular process required for the survival of all organisms. In protists, the need for robust compensatory mechanisms that can maintain cell volume and tonicity within physiological range is even more relevant, as their life cycles are often completed in different environments. Trypanosoma cruzi, the protozoan pathogen responsible for Chagas disease, is transmitted by an insect vector to multiple types of mammalian hosts. The contractile vacuole complex (CVC) is an organelle that senses and compensates osmotic changes in the parasites, ensuring their survival upon ionic and osmotic challenges. Recent work shows that the contractile vacuole is also a key component of the secretory and endocytic pathways, regulating the selective targeting of surface proteins during differentiation. Here we summarize our current knowledge of the mechanisms involved in the osmoregulatory processes that take place in the vacuole, and we explore the new and exciting functions of this organelle in cell trafficking and signaling.

New contributions to the Cyrtophoria ciliates (Protista, Ciliophora): Establishment of new taxa and phylogenetic analyses using two ribosomal genes.

Periphytic ciliates play a vital role in the material cycle and energy flow of microbial food web, however, their taxonomy and biodiversity are inadequately studied given their high species richness. Two new and one little known species, viz. Derouxella lembodes gen. et sp. nov., Cyrtophoron multivacuolatum sp. nov., and Cyrtophoron apsheronica Aliev, 1991, collected from coastal waters of China, were investigated using modern methods. Derouxella gen. nov. can be recognized by having dorsoventrally flattened body, a podite, one fragmented preoral kinety, two parallel circumoral kineties, and somatic kineties progressively shortened from right to left. Morphological classification and phylogenetic analyses based on nuclear small subunit ribosomal RNA (nSSU rRNA) and mitochondrial small subunit ribosomal RNA (mtSSU rRNA) gene sequence data inferred that Derouxella gen. nov. occupies an intermediate position between Hartmannulidae and Dysteriidae. Cyrtophoron multivacuolatum sp. nov. is characterized by large body size, the numbers of somatic kineties and nematodesmal rods, and having numerous contractile vacuoles. The genus Cyrtophoron and the poorly known species C. apsheronica were redefined. Even with the addition of newly obtained nSSU rRNA and mtSSU rRNA gene sequencesof Cyrtophoron, the family Chlamydodontidae was still recovered as a monophyletic group, the monophyly of Cyrtophoron was supported too.

Morphology and SSU rRNA gene-based phylogeny of three peniculid ciliates (Ciliophora, Oligohymenophorea) from China, including a new Frontonia species

In the present study, a new freshwater peniculid species, Frontonia apoelegans sp. nov., and two other peniculid species, Frontonia atra (Ehrenberg, 1833) Bütschli, 1889 and Stokesia vernalis Wenrich, 1929, were isolated from Lake Weishan wetland, northern China. Their morphology and infraciliature are described based on live observations and silver staining methods. The SSU rRNA gene sequences are also provided. Frontonia apoelegans sp. nov. is recognized by the following combination of characteristics: two contractile vacuoles located right-dorsally, without collecting canals; peniculi 1 and 2 four-rowed, peniculus 3 three-rowed with leftmost row containing only one kinetosome; 62–76 somatic kineties; three ophryokineties; and four or five postoral kineties. We also provide improved diagnoses for Frontonia atra and Stokesia vernalis based on current and previous reports. Comparisons with sequences of morphologically similar species clearly support the validity of the new species. Phylogenetic analyses based on SSU rRNA gene sequence data reveal that Frontonia species with two contractile vacuoles cluster in a single clade, indicating these species may have a common origin. The family Frontoniidae is non-monophyletic whereas the family Stokesiidae remains monophyletic according to our analyses.

The Polarized Redistribution of the Contractile Vacuole to the Rear of the Cell is Critical for Streaming and is Regulated by PI(4,5)P2-Mediated Exocytosis

Dictyostelium discoideum amoebae align in a head to tail manner during the process of streaming during fruiting body formation. The chemoattractant cAMP is the chemoattractant regulating cell migration during this process and is released from the rear of cells. The process by which this cAMP release occurs has eluded investigators for many decades, but new findings suggest that this release can occur through expulsion during contractile vacuole (CV) ejection. The CV is an organelle that performs several functions inside the cell including the regulation of osmolarity, and discharges its content via exocytosis. The CV localizes to the rear of the cell and appears to be part of the polarity network, with the localization under the influence of the plasma membrane (PM) lipids, including the phosphoinositides (PIs), among those is PI(4,5)P2, the most abundant PI on the PM. Research on D. discoideum and neutrophils have shown that PI(4,5)P2 is enriched at the rear of migrating cells. In several systems, it has been shown that the essential regulator of exocytosis is through the exocyst complex, mediated in part by PI(4,5)P2-binding. This review features the role of the CV complex in D. discoideum signaling with a focus on the role of PI(4,5)P2 in regulating CV exocytosis and localization. Many of the regulators of these processes are conserved during evolution, so the mechanisms controlling exocytosis and membrane trafficking in D. discoideum and mammalian cells will be discussed, highlighting their important functions in membrane trafficking and signaling in health and disease.

Molecular evolutionary analysis of the SM and SNARE vesicle fusion machinery in ciliates shows concurrent expansions in late secretory machinery.

Protists in the phylum Ciliophora possess a complex membrane-trafficking system, including osmoregulatory Contractile Vacuoles and specialized secretory organelles. Molecular cell biological investigations in Tetrahymena thermophila have identified components of the protein machinery associated with the secretory organelles, mucocysts. The Qa-SNARE Syn7lp plays a role in mucocyst biogenesis as do subunits of the CORVET tethering complex (specifically Vps8). Indeed, Tetrahymena thermophila possesses expanded gene complements of several CORVET components, including Vps33 which is also a Sec1/Munc18 (SM) protein that binds Qa-SNAREs. Moreover, the Qa-SNAREs in Paramecium tetraurelia have been localized to various endomembrane organelles. Here, we use comparative genomics and phylogenetics to determine the evolutionary history of the SM and Qa-SNARE proteins across the Ciliophora. We identify that the last ciliate common ancestor possessed the four SM proteins and six Qa-SNAREs common to eukaryotes, including the uncommonly retained Syntaxin 17. We furthermore identify independent expansion of these protein families in several ciliate classes, including concurrent expansions of the SM protein-Qa SNARE partners Sec1:SynPM in the oligohymenophorean ciliates lineage, consistent with novel Contractile Vacuole specific innovations. Overall, these data are consistent with SM proteins and Qa-SNAREs being a common set of components for endomembrane modulation in the ciliates.

Targeting the Contractile Vacuole of Parasites

The contractile vacuole (CV) is a poorly studied organelle involved in osmotic regulation. In every contraction cycle, the CV expels excess liquid to maintain osmoregulation. CVs are found in single‐celled eukaryotes including parasitic and free‐living ciliates. Parasitic examples include Trypanosoma cruzi, amoebas, and Leishmaniaparasites. We use the free‐living ciliate Vorticella convallaria as a model for CV cycling, which can be observed directly under a microscope. The CV contraction rate in Vorticella convallaria,increases with temperature within physiologically relevant non‐lethal temperature ranges. We performed a historical literature review of CV cycling rates and temperature across ciliates and amoeba. The Arrhenius equation was used to calculate the activation energy barrier for CV contraction. The slope of the Arrhenius graph was similar across all organisms ranging from 6000 to 17000 calories (per mol CV cycle), suggesting that conserved chemical or physical processes control CV cycling across biology. Future research will investigate whether using drugs to inhibit the CV will change the slope of the Arrhenius graph in Vorticella convallaria,and whether those same drugs will exacerbate osmotic cell death in the parasite Crithidia fasciculata. Ultimately, our results may contribute to the development of anti‐parasitic drugs targeting parasites’ unique CV organelle.

Osmotic stress and regulatory volume decrease in Crithidia fasciculataparasites

Regulatory volume decrease (RVD) describes the response to hypoosmotic stress in many cells including the parasitic flagellate Crithidia fasciculata. Hypoosmotic stress causes initial swelling, the cell expels excess liquid and returns to a normal volume. This process is not able to withstand excessive osmotic stress. We use the MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide) Assay is used to assess cell viability, while microscopy images and spectroscopic light scatter used to follow changes in cell shape and size. It was found that after being placed in 70% hypotonic (30% isotonic) solution, cells did not recover from hypoosmotic stress. We are currently developing protocols for this little‐studied parasite and investigating the mechanisms of RVD in Crithidia fasciculata including the role of the osmoregulatory contractile vacuole.

Iron metabolism in the social amoeba Dictyostelium discoideum: A role for ferric chelate reductases

Iron is the most abundant transition metal in all living organisms and is essential for several cellular activities, including respiration, oxygen transport, energy production and regulation of gene expression. Iron starvation is used by professional phagocytes, from Dictyostelium to macrophages, as a form of defense mechanism against intracellular pathogens. Previously, we showed that Dictyostelium cells express the proton-driven iron transporter Nramp1 (Natural Resistance-Associated Macrophage Protein 1) and the homolog NrampB (Nramp2) in membranes of macropinosomes and phagosomes or of the contractile vacuole network, respectively. The Nramp-driven transport of iron across membranes is selective for ferrous ions. Since iron is mostly present as ferric ions in growth media and in engulfed bacteria, we have looked for proteins with ferric reductase activity. The Dictyostelium genome does not encode for classical STEAP (Six-Transmembrane Epithelial Antigen of Prostate) ferric reductases, but harbors three genes encoding putative ferric chelate reductase belonging to the Cytochrome b561 family containing a N terminus DOMON domain (DOpamine β-MONooxygenase N-terminal domain). We have cloned the three genes, naming them fr1A, fr1B and fr1C. fr1A and fr1B are mainly expressed in the vegetative stage while fr1C is highly expressed in the post aggregative stage. All three reductases are localized in the endoplasmic reticulum, but Fr1A is also found in endolysosomal vesicles, in the Golgi and, to a much lower degree, in the plasma membrane, whereas Fr1C is homogeneously distributed in the plasma membrane and in macropinosomal and phagosomal membranes. To gain insight in the function of the three genes we generated KO mutants, but gene disruption was successful only for two of them (fr1A and fr1C), being very likely lethal for fr1B. fr1A- shows a slight delay in the aggregation stage of development, while fr1C- gives rise to large multi-tipped streams during aggregation and displays a strong delay in fruiting body formation. The two single mutants display altered cell growth under conditions of ferric ions overloading and, in the ability to reduce Fe3+, confirming a role of these putative ferric reductases in iron reduction and transport from endo-lysosomal vesicles to the cytosol.

Updating the phylogeny and taxonomy of pleurostomatid ciliates (Protista: Ciliophora) with establishment of a new family, a new genus and two new species

AbstractThe order Pleurostomatida is one of the most confusing groups in the ciliate class Litostomatea. In the present study, two new species, Paralitonotus foissneri gen. & sp. nov. and Loxophyllum apochlorelligerum sp. nov., were investigated using an integrative approach. Paralitonotus foissneri differs from other pleurostomatids by its distinctive ciliary pattern (i.e. the anterior ends of the right somatic kineties are progressively shortened from the middle towards dorsal and perioral ones). Therefore, we place it in the new genus Paralitonotus. Loxophyllum apochlorelligerum is characterized by seven to nine left and 12–14 right somatic kineties, three to five anterior dorsal warts and a subterminal contractile vacuole. Phylogenetic analyses show that Pa. foissneri clusters with Apolitonotus lynni and Pseudolitonotus gracilis to form a deep-branching subclade that is basal to other core pleurostomatids. All three genera have distinctive anteriorly shortened right kineties, suggesting that this might be a familial character state. We therefore establish a new family, Paralitonotidae fam. nov., for pleurostomatids with this character and propose a new taxonomic scheme and a hypothetical evolutionary trajectory of the order Pleurostomatida. In addition, the generic diagnostic characters for pleurostomatids are updated, and a key to the identification of pleurostomatid genera is provided.

Ultrastructure and phylogeny of Parietochloris toyamaensis sp. nov. and P. bilobata (Trebouxiophyceae)

We describe Parietochloris toyamaensis sp. nov. and verify the taxonomic status of P. bilobata (originally described as Neochloris and once combined with Ettlia), using ultrastructural and molecular analyses. P. toyamaensis was isolated from soil collected in Toyama, Japan. It had a parietal chloroplast with pyrenoids that were discontinuously covered with starch segments and penetrated more or less in parallel by thylakoid membranes, and reproduced by forming naked, somewhat dorsoventral, biflagellate zoospores. Two contractile vacuoles were in line lengthwise, located in the median ventral side of the zoospores, as in the type P. alveolaris. The basal apparatus components included a single microtubule in the dexter root. P. toyamaensis was separately resolved from other members of the genus in the 18S rDNA and ITS2 trees. Since the authentic strain ASIB V141 of P. bilobata (stored as Ettlia) has been lost, ASIB V143 was used as a reference in place of it. P. bilobata ASIB V143 was resolved in the ‘Parietochloris sensu stricto’ clade but not ‘Lobosphaera’ clade in the 18S rDNA tree, so taxonomically the combination of N. bilobata with Parietochloris as P. bilobata by Andreyeva was confirmed. In zoospores of the strains of P. bilobata, contractile vacuoles were located in the ventral side, as in P. alveolaris. The taxonomic relationship between P. bilobata and P. grandis, and evaluation of the unique position of contractile vacuoles in dorsoventral zoospores as one of the key characters of Parietochloris were discussed.

Taxonomic and phylogenetic studies on two new freshwater Amphileptus species (Ciliophora, Pleurostomatida), from Lake Weishan, northern China

The morphology and phylogeny of two new species of pleurostomatid ciliates, Amphilepus weishanensis sp. nov. and A. parapleurosigma sp. nov., collected from Lake Weishan in northern China, were studied using live observation, protargol staining and phylogenetic analyses based on small subunit ribosomal DNA (SSU rDNA) sequence data. In both species, extrusomes form an apical group and contractile vacuoles are distributed along both the dorsal and the ventral margin. Amphileptus weishanensis sp. nov. is characterized by its body size (560–780 × 60–100 μm in vivo) and the possession of five left and 56–61 right somatic kineties, filiform extrusomes and 3–9 macronuclear nodules. Amphileptus parapleurosigma sp. nov. is characterized by possessing 4–6 left and 19–24 right somatic kineties and clavate extrusomes. The SSU rDNA sequences differ among ten similar species by 3–60 bp. Phylogenetic analyses based on the SSU rDNA sequences indicate that the family Amphileptidae is monophyletic while Amphileptus is paraphyletic with Pseudoamphileptus nesting within this genus.

Taxonomy and systematics of a new pleurostomatid ciliate, Pseudolitonotus spirelis gen. et sp. n. (Protozoa, Ciliophora, Haptoria).

Recent studies have revealed a high diversity of pleurostomatid ciliates in brackish habitats. Here, a novel species, Pseudolitonotus spirelis gen. et sp. n., isolated from a mangrove wetland of southern China, was investigated based on living observation, protargol staining, and molecular analyses. The new genus Pseudolitonotus gen. n. is characterized by the last left somatic kinety (LKn) being shortened and none of the right somatic kineties extending to the anterior end of the cell, thus distinguishing it from all known pleurostomatid genera. The type species, Pseudolitonotus spirelis sp. n., is characterized by the possession of two macronuclear nodules, 11-15 right and 7-9 left kineties, a single contractile vacuole subterminally located, extrusomes evenly spaced along the entire ventral margin and some forming an "apical group", two types of cortical granules, and the bottom of the oral slit invariably being twisted. Litonotus gracilis (Pan et al. Eur J Protistol 51:494-506, 2015) is believed to be another member of this new genus as its LKn and right somatic kineties are all shortened. Hence, a new combination, Pseudolitonotus gracilis (Pan et al., 2015) comb. n., is suggested and its diagnosis is improved. Molecular phylogenetic analyses based on SSU rDNA sequence data reveal that Pseudolitonotus gen. n. is monophyletic and groups with Apolitonotus (Pan et al. J Eukaryot Microbiol 67:252-262, 2020) of the family Protolitonotidae (Wu et al. Zool Scr 46:245-253, 2017). However, the familial assignment of this new genus is uncertain based on current data.

Taxonomy and molecular phylogeny of a new freshwater ciliate Frontonia apoacuminata sp. nov. (Protista, Ciliophora, Oligohymenophorea) from Qingdao, PR China.

The morphology and ciliature of a new freshwater ciliate, Frontonia apoacuminata sp. nov., isolated from an artificial pond in Qingdao, PR China, were investigated using live observation and silver staining methods. The main features separating F. apoacuminata sp. nov. from its congeners are as follows: a broad elliptical body that is slightly pointed at the posterior end, four ophryokineties, one or two spherical micronuclei of a 'compact' type, a dorsally positioned contractile vacuole, and peniculi 1-3 each with five kinetosome rows though the left-most two rows in peniculus 3 are extremely shortened (with only two or three kinetosomes each). Additionally, an improved diagnosis of F. acuminata is provided. Phylogenetic analyses based on the small subunit ribosomal RNA (SSU rRNA) gene show that F. apoacuminata sp. nov. clusters with F. atra, F. minuta, F. acuminata and F. terricola. These five species group with Disematostoma, Marituja and Stokesia rather than with other Frontonia species, causing polyphyly of the genus Frontonia.

Systematic review of the genus Ostracodinium (Ciliophora, Entodiniomorphida, Ophryoscolecidae) and notes on the taxonomy of Ostracodinium rugoloricatum Kofoid amp; MacLennan, 1932.

The family Ophryoscolecidae (Ciliophora, Entodiniomorphida) constitutes a diverse and monophyletic group of symbiotic ciliates of herbivorous mammals. The family includes approximately 200 species, distributed in three subfamilies and sixteen genera. The subfamily Diplodiniinae is the most diverse group in Ophryoscolecidae and comprises the genus Ostracodinium, which includes species with two retractable ciliary zones in the anterior body portion, a broad skeletal plate covering almost all the right surface of the body and a variable number of contractile vacuoles. The genus currently comprises 28 species, classified according to body size and shape, position and shape of the nuclear apparatus, number and position of contractile vacuoles, and number and shape of caudal projections. The present study performs a systematic review of the genus Ostracodinium, based on morphological and molecular data, and provides data about geographic distribution and hosts of each species.

A novel mechanosensitive channel controls osmoregulation, differentiation, and infectivity in Trypanosoma cruzi.

The causative agent of Chagas disease undergoes drastic morphological and biochemical modifications as it passes between hosts and transitions from extracellular to intracellular stages. The osmotic and mechanical aspects of these cellular transformations are not understood. Here we identify and characterize a novel mechanosensitive channel in Trypanosoma cruzi (TcMscS) belonging to the superfamily of small-conductance mechanosensitive channels (MscS). TcMscS is activated by membrane tension and forms a large pore permeable to anions, cations, and small osmolytes. The channel changes its location from the contractile vacuole complex in epimastigotes to the plasma membrane as the parasites develop into intracellular amastigotes. TcMscS knockout parasites show significant fitness defects, including increased cell volume, calcium dysregulation, impaired differentiation, and a dramatic decrease in infectivity. Our work provides mechanistic insights into components supporting pathogen adaptation inside the host, thus opening the exploration of mechanosensation as a prerequisite for protozoan infectivity.