Cyst and encystment in protozoan parasites: optimal targets for new life-cycle interrupting strategies?

Role of chitin synthases CHS1 and CHS2 in biosynthesis of the cyst wall of Cryptocaryon irritans

Cryptocaryon irritans, a protozoan parasite that infects marine fish, is characterized by a complex life cycle that includes a cyst-forming reproductive phase. However, the composition of the cyst wall and mechanism of its formation remain unclear. In this study, we identified chitin as a key component of the cyst wall using calcofluor white and wheat germ agglutinin, with Fourier-transform infrared spectroscopy confirming its β-form structure. Two chitin synthase genes, CHS1 and CHS2, were identified as being expressed throughout the life cycle and show close phylogenetic relationships with chitin synthase from ciliates. Incubation with specific anti-CHS1 and -CHS2 antibodies significantly reduced both the thickness and chitin content of the cyst wall, highlighting the critical role of these enzymes in chitin biosynthesis. Treatment with benzoylureas, which inhibit chitin synthesis, caused thinning of the cyst wall and downregulation of CHS gene expression, resulting in an 84 % reduction in the hatching rate after treatment with 0.01 mM CuSO4 compared with control tomonts. Western blot analysis demonstrated that recombinant CHS proteins are immunogenic, and tomonts from CHS-immunized grouper exhibited reduced size. These findings bridge a crucial knowledge gap in understanding of the C. irritans cyst wall and highlight promising targets for infection prevention and control strategies.

Comparing the Environmental Influences and Community Assembly of Protist Communities in Two Anthropogenic Coastal Areas

Anthropogenic stresses are intensively affecting the structure and function of microbial communities in coastal ecosystems. Despite being essential components of coastal ecosystems, the environmental influences and assembly processes of protist communities remain largely unknown in areas with severe disturbance. Here, we used 18S rRNA gene high-throughput sequencing to compare the composition, assembly process, and functional structure of the protist communities from the coastal areas of the Northern Yellow Sea (NYS) and the Eastern Bohai Sea (EBS). These two areas are separated by the Liaodong Peninsula and experience different anthropogenic stresses due to varying degrees of urbanization. We detected significant differences between the protist communities of the two areas. Environmental and geographic factors both influenced the composition of protist communities, with environmental factors playing a greater role. The neutral community model indicated that the assembly of protist communities was governed by deterministic processes, with stochastic processes having a stronger influence in the EBS area compared to the NYS area. The phototrophic and consumer communities, influenced by different environmental factors, differed significantly between the two areas. Our results provide insights into the biogeography and assembly of protist communities in estuaries under anthropogenic stresses, which may inform future coastal management.

Introducing the NUATEI Consortium: A Mexican Research Program for the Identification of Natural and Synthetic Antimicrobial Compounds for Prevalent Infectious Diseases

The need for new drugs to treat human infections is a global health concern. Diseases like tuberculosis, trypanosomiasis, amoebiasis, and AIDS remain significant problems, especially in developing countries like Mexico. Despite existing treatments, issues such as resistance and adverse effects drive the search for new alternatives. Herein, we introduce the NUATEI research consortium, made up of experts from the Institute of Biomedical Research at UNAM, who identify and obtain natural and synthetic compounds and test their effects against human pathogens using in vitro and in vivo models. The consortium has evaluated hundreds of natural extracts and compounds against the pathogens causing tuberculosis, trypanosomiasis, amoebiasis, and AIDS, rendering promising results, including a patent with potential for preclinical studies. This paper presents the rationale behind the formation of this consortium, as well as its objectives and strategies, emphasizing the importance of natural and synthetic products as sources of antimicrobial compounds and the relevance of the diseases studied. Finally, we briefly describe the methods of the evaluation of the compounds in each biological model and the main achievements. The potential of the consortium to screen numerous compounds and identify new therapeutic agents is highlighted, demonstrating its significant contribution to addressing these infectious diseases.

Palmelloid-like phenotype in the alga Raphidocelis subcapitata exposed to pollutants: A generalized adaptive strategy to stress or a specific cellular response?

This work focuses on the formation of palmelloid-like phenotype in the freshwater alga Raphidocelis subcapitata (formerly known as Pseudokirchneriella subcapitata and Selenastrum capricornutum), when exposed to adverse conditions generated by the presence of organic [the antibiotic erythromycin (ERY) and the herbicide metolachlor (MET)] or inorganic [the heavy metals, cadmium (Cd) and zinc (Zn)] pollutants, at environmentally relevant concentrations. This alga in absence of stress or when exposed to ERY or Zn, up to 200 µg/L, essentially showed a single-nucleus state, although algal growth was reduced or stopped. R. subcapitata "switched" to a multinucleated state (palmelloid-like morphology) and accumulated energy-reserve compounds (neutral lipids) when stressed by 100-200 µg/L MET or 200 µg/L Cd; at these concentrations of pollutants, growth was arrested, however, the majority of the algal population (≥83 %) was alive. The formation of palmelloid-like phenotype, at sub-lethal concentrations of pollutants, was dependent on the pollutant, its concentration and exposure time. The multinucleated structure is a transitory phenotype since R. subcapitata population was able to revert to a single-nucleus state, with normal cell size, within 24-96 h (depending on the impact of the toxic in the alga), after being transferred to fresh OECD medium, without pollutants. The obtained results indicate that the formation of a palmelloid-like phenotype in R. subcapitata is dependent on the mode of action of toxics and their concentration, not constituting a generalized defense mechanism against stress. The observations here shown contribute to understanding the different strategies used by the unicellular alga R. subcapitata to cope with severe stress imposed by organic and inorganic pollutants.

Entamoeba histolytica induced NETosis and the dual role of NETs in amoebiasis

Entamoeba histolytica (Eh), a microaerophilic parasite, causes deadly enteric infections that result in Amoebiasis. Every year, the count of invasive infections reaches 50 million approximately and 40,000 to 1,00,000 deaths occurring due to amoebiasis are reported globally. Profound inflammation is the hallmark of severe amoebiasis which is facilitated by immune first defenders, neutrophils. Due to size incompatibility, neutrophils are unable to phagocytose Eh and thus, came up with the miraculous antiparasitic mechanism of neutrophil extracellular traps (NETs). This review provides an in-depth analysis of NETosis induced by Eh including the antigens involved in the recognition of Eh and the biochemistry of NET formation. Additionally, it underscores its novelty by describing the dual role of NETs in amoebiasis where it acts as a double-edged sword in terms of both clearing and exacerbating amoebiasis. It also provides a comprehensive account of the virulence factors discovered to date that are implicated directly and indirectly in the pathophysiology of Eh infections through the lens of NETs and can be interesting drug targets.

A myeloid leukemia factor homolog is involved in tolerance to stresses and stress-induced protein metabolism in Giardia lamblia

BACKGROUND

The eukaryotic membrane vesicles contain specific sets of proteins that determine vesicle function and shuttle with specific destination. Giardia lamblia contains unknown cytosolic vesicles that are related to the identification of a homolog of human myeloid leukemia factor (MLF) named MLF vesicles (MLFVs). Previous studies suggest that MLF also colocalized with two autophagy machineries, FYVE and ATG8-like protein, and that MLFVs are stress-induced compartments for substrates of the proteasome or autophagy in response to rapamycin, MG132, and chloroquine treatment. A mutant protein of cyclin-dependent kinase 2, CDK2m3, was used to understand whether the aberrant proteins are targeted to degradative compratments. Interestingly, MLF was upregulated by CDK2m3 and they both colocalized within the same vesicles. Autophagy is a self-digestion process that is activated to remove damaged proteins for preventing cell death in response to various stresses. Because of the absence of some autophagy machineries, the mechanism of autophagy is unclear in G. lamblia.

RESULTS

In this study, we tested the six autophagosome and stress inducers in mammalian cells, including MG132, rapamycin, chloroquine, nocodazole, DTT, and G418, and found that their treatment increased reactive oxygen species production and vesicle number and level of MLF, FYVE, and ATG8-like protein in G. lamblia. Five stress inducers also increased the CDK2m3 protein levels and vesicles. Using stress inducers and knockdown system for MLF, we identified that stress induction of CDK2m3 was positively regulated by MLF. An autophagosome-reducing agent, 3-methyl adenine, can reduce MLF and CDK2m3 vesicles and proteins. In addition, knockdown of MLF with CRISPR/Cas9 system reduced cell survival upon treatment with stress inducers. Our newly developed complementation system for CRISPR/Cas9 indicated that complementation of MLF restored cell survival in response to stress inducers. Furthermore, human MLF2, like Giardia MLF, can increase cyst wall protein expression and cyst formation in G. lamblia, and it can colocalize with MLFVs and interact with MLF.

CONCLUSIONS

Our results suggest that MLF family proteins are functionally conserved in evolution. Our results also suggest an important role of MLF in survival in stress conditions and that MLFVs share similar stress-induced characteristics with autophagy compartments.

Inactivation of Giardia intestinalis cysts in water using a sonochemical method based on mid-high-frequency waves

Giardia intestinalis is a pollutant of food and water, resistant to conventional disinfection treatments and its elimination requires effective methods action. Herein, mid-high-frequency ultrasound (375 kHz), which produces HO• and H₂O₂, was used as an alternative method of treatment to inactivate Giardia intestinalis cysts in water. The effect of ultrasound power (4.0, 11.2, 24.4 W) on the sonogeneration of radicals was tested, showing that 24.4 W was the condition most favorable to treat the parasite. The viability of the protozoan cysts was evaluated using the immunofluorescence technique and vital stains, showing this protocol was useful to quantify the parasite. The sonochemical method (at 375 kHz and 24.4 W) was applied at different treatment times (10, 20, and 40 min). A significant decrease in the protozoan concentration (reduction of 52.4% of viable cysts) was observed after 20 min of treatment. However, the extension of treatment time up to 40 min did not increase the inactivation. Disinfecting action was associated with attacks on the Giardia intestinalis cyst by sonogenerated HO• and H₂O₂ (which may induce structural damage, even the cell lysis). For future work is recommended to test combinations with UVC or Fenton process to enhance the inactivating action of this method.•Mid-high-frequency ultrasound produces HO• and H₂O₂ profitable to inactivate Giardia intestinalis.•Immunofluorescence technique and vital stains allowed us to quantify the parasite viability.•Giardia intestinalis cysts concentration decreased by 52.4% after only 20 min of sonication.

Immunomodulatory effect of extracellular vesicles from Entamoeba histolytica trophozoites: Regulation of NETs and respiratory burst during confrontation with human neutrophils

Parasites release extracellular vesicles (EVs) which, in some cases, modulate the host's immune response contributing to the establishment of the infection. In this work we have isolated and characterized the EVs released by trophozoites of the human protozoan parasite Entamoeba histolytica, the causal agent of amoebiasis, when alone or in coculture with human neutrophils, and determined their effect on neutrophil NETs and ROS production. Nanoparticle tracking analysis showed that amoebic EVs are variable in size, ranging from less than 50 nm to nearly 600 nm in diameter (average of 167 nm), whereas neutrophil EVs are more uniform in size, with an average of 136 nm. In cocultures amoeba:neutrophil (1:100) most EVs are 98 nm in size, which is the typical size of exosomes. EVs from amoebae and neutrophils showed almost equal levels of ROS, which were considerably increased in EVs from cocultures. Uptake of amoebic EVs by neutrophils was demonstrated by fluorescence and resulted in a significant reduction in the oxidative burst and NET release triggered by PMA, ionophore A23187, or the amoebae itself used as stimuli. Interestingly, uptake of EVs from cocultures did not affect ROS production, but instead caused a greater delay in the onset of NETs release and in their quantity. A comparative proteomic analysis between the EVs of amoebae and neutrophils separately vs the cocultures showed a similar distribution of protein categories in the GO analysis, but differences in the expression and abundance of proteins such as the N-acetyl-D-galactosamine (GalNAc) inhibitable surface lectin and calreticulin in amoeba EVs, and various antimicrobial molecules in neutrophil EVs, such as lactoferrin and myeloperoxidase. These results highlight the importance of EVs in the immunomodulatory effects exerted by amoeba on human neutrophils.

Activity of Apo-Lactoferrin on Pathogenic Protozoa

Parasites and other eventually pathogenic organisms require the ability to adapt to different environmental conditions inside the host to assure survival. Some host proteins have evolved as defense constituents, such as lactoferrin (Lf), which is part of the innate immune system. Lf in its iron-free form (apo-Lf) and its peptides obtained by cleavage with pepsin are microbicides. Parasites confront Lf in mucosae and blood. In this work, the activity of Lf against pathogenic and opportunistic parasites such as Cryptosporidium spp., Eimeria spp., Entamoeba histolytica, Giardia duodenalis, Leishmania spp., Trypanosoma spp., Plasmodium spp., Babesia spp., Toxoplasma gondii, Trichomonas spp., and the free-living but opportunistic pathogens Naegleria fowleri and Acanthamoeba castellani were reviewed. The major effects of Lf could be the inhibition produced by sequestering the iron needed for their survival and the production of oxygen-free radicals to more complicated mechanisms, such as the activation of macrophages to phagocytes with the posterior death of those parasites. Due to the great interest in Lf in the fight against pathogens, it is necessary to understand the exact mechanisms used by this protein to affect their virulence factors and to kill them.

Diversity of Lysis-Resistant Bacteria and Archaea in the Polyextreme Environment of Salar de Huasco

The production of specialized resting cells is a remarkable strategy developed by several organisms to survive unfavorable environmental conditions. Spores are specialized resting cells that are characterized by low to absent metabolic activity and higher resistance. Spore-like cells are known from multiple groups of bacteria, which can form spores under suboptimal growth conditions (e.g., starvation). In contrast, little is known about the production of specialized resting cells in archaea. In this study, we applied a culture-independent method that uses physical and chemical lysis, to assess the diversity of lysis-resistant bacteria and archaea and compare it to the overall prokaryotic diversity (direct DNA extraction). The diversity of lysis-resistant cells was studied in the polyextreme environment of the Salar de Huasco. The Salar de Huasco is a high-altitude athalassohaline wetland in the Chilean Altiplano. Previous studies have shown a high diversity of bacteria and archaea in the Salar de Huasco, but the diversity of lysis-resistant microorganisms has never been investigated. The underlying hypothesis was that the combination of extreme abiotic conditions might favor the production of specialized resting cells. Samples were collected from sediment cores along a saline gradient and microbial mats were collected in small surrounding ponds. A significantly different diversity and composition were found in the sediment cores or microbial mats. Furthermore, our results show a high diversity of lysis-resistant cells not only in bacteria but also in archaea. The bacterial lysis-resistant fraction was distinct in comparison to the overall community. Also, the ability to survive the lysis-resistant treatment was restricted to a few groups, including known spore-forming phyla such as Firmicutes and Actinobacteria. In contrast to bacteria, lysis resistance was widely spread in archaea, hinting at a generalized resistance to lysis, which is at least comparable to the resistance of dormant cells in bacteria. The enrichment of Natrinema and Halarchaeum in the lysis-resistant fraction could hint at the production of cyst-like cells or other resistant cells. These results can guide future studies aiming to isolate and broaden the characterization of lysis-resistant archaea.

Environmental and biological drivers of prevalence and number of eggs and oocysts of intestinal parasites in red howler monkeys from Central Amazonia

Host-parasite relationships can be directly affected by host’s biological aspects and environmental factors, which influence both the survival of infective forms and the incidence of parasites. However, logistical difficulties in accessing biological samples for parasitological studies makes the Amazon Forest into a poorly known region in relation to the dynamic of parasites of wild animals. Here, using 34 red howler monkeys’ biological samples donated by local subsistence hunters from two Amazon habitat types (white-water flooded forest and upland forest) as an opportune alternative, we detected four intestinal parasite taxa infecting this species (two nematodes – Trypanoxyuris sp. and Strongyloides sp., one protozoan – Entamoeba sp. –, and one not-identified trematode, the last just found for white-water flooded forest). Trypanoxyuris was the most prevalent intestinal parasite (56.5% at flooded forest and 54.5% at upland forest). There was no difference between habitat types or individual sex regarding the prevalence for any parasite taxa. On the other hand, we found a strong influence of seasonality, with increasing prevalence of all parasite taxa as the river water level increased. In terms of egg and cyst counts, we found a difference between sexes (females > males, p = 0.002) and habitat types (upland forest > white-water flooded forest, p = 0.02), and a positive relationship with river water level (p = 0.002). Although some of these parasite taxa can be shared between humans and howlers, further investigations are necessary to study the parasites taxonomy thoroughly and to assess the potential zoonotic cross-transmission of these pathogens to local people living in the Amazon. In this study, we unveiled a seasonal effect for howler monkeys’ intestinal parasites, that also might occur in other non-human primates of the Amazon. In addition, our results on periods of high risk of intestinal parasite infection are useful to estimate future impacts of climate change on host-parasite dynamics.

Using Genomic Deletion Mutants to Investigate Effector-Triggered Immunity During Legionella pneumophila Infection

Legionella pneumophila is an intracellular bacterial pathogen that uses a type IV secretion system (T4SS), termed Dot/Icm, to secrete more than 330 virulence effector proteins into the infected host cell. Many Dot/Icm effectors are involved in biogenesis of the Legionella-containing vacuole (LCV), which allows intracellular bacterial replication in environmental amoebae and alveolar macrophages. Through their activity, some effectors trigger the mammalian host immune response in a phenomenon termed effector-triggered immunity (ETI). Here, we describe a protocol to create and use L. pneumophila genome deletion mutants to identify effector(s) that alter pro-inflammatory cytokine production and bacterial clearance in the lungs of mice.

Multilevel Approach for the Treatment of Giardiasis by Targeting Arginine Deiminase

Giardiasis represents a latent problem in public health due to the exceptionally pathogenic strategies of the parasite Giardia lamblia for evading the human immune system. Strains resistant to first-line drugs are also a challenge. Therefore, new antigiardial therapies are urgently needed. Here, we tested giardial arginine deiminase (GlADI) as a target against giardiasis. GlADI belongs to an essential pathway in Giardia for the synthesis of ATP, which is absent in humans. In silico docking with six thiol-reactive compounds was performed; four of which are approved drugs for humans. Recombinant GlADI was used in enzyme inhibition assays, and computational in silico predictions and spectroscopic studies were applied to follow the enzyme's structural disturbance and identify possible effective drugs. Inhibition by modification of cysteines was corroborated using Ellman's method. The efficacy of these drugs on parasite viability was assayed on Giardia trophozoites, along with the inhibition of the endogenous GlADI. The most potent drug against GlADI was assayed on Giardia encystment. The tested drugs inhibited the recombinant GlADI by modifying its cysteines and, potentially, by altering its 3D structure. Only rabeprazole and omeprazole decreased trophozoite survival by inhibiting endogenous GlADI, while rabeprazole also decreased the Giardia encystment rate. These findings demonstrate the potential of GlADI as a target against giardiasis.

Antimicrobial resistance of the enteric protozoon Giardia duodenalis - A narrative review

Introduction

As therapy-refractory giardiasis is an emerging health issue, this review aimed at summarizing mechanisms of reduced antimicrobial susceptibility in Giardia duodenalis and strategies to overcome this problem.

Methods

A narrative review on antimicrobial resistance in G. duodenalis was based upon a selective literature research.

Results

Failed therapeutic success has been observed for all standard therapies of giardiasis comprising nitroimidazoles like metronidazole or tinidazole as first line substances but also benznidazoles like albendazole and mebendazole, the nitrofuran furazolidone, the thiazolide nitazoxanide, and the aminoglycoside paromomycin. Multicausality of the resistance phenotypes has been described, with differentiated gene expression due to epigenetic and post-translational modifications playing a considerable bigger role than mutational base exchanges in the parasite DNA. Standardized resistance testing algorithms are not available and clinical evidence for salvage therapies is scarce in spite of research efforts targeting new giardicidal drugs.

Conclusion

In case of therapeutic failure of first line nitroimidazoles, salvage strategies including various options for combination therapy exist in spite of limited evidence and lacking routine diagnostic-compatible assays for antimicrobial susceptibility testing in G. duodenalis. Sufficiently powered clinical and diagnostic studies are needed to overcome both the lacking evidence regarding salvage therapy and the diagnostic neglect of antimicrobial resistance.

Aptamers and Aptamer-Coupled Biosensors to Detect Water-Borne Pathogens

Aptamers can serve as efficient bioreceptors for the development of biosensing detection platforms. Aptamers are short DNA or RNA oligonucleotides that fold into specific structures, which enable them to selectively bind to target analytes. The method used to identify aptamers is Systematic Evolution of Ligands through Exponential Enrichment (SELEX). Target properties can have an impact on aptamer efficiencies. Therefore, characteristics of water-borne microbial targets must be carefully considered during SELEX for optimal aptamer development. Several aptamers have been described for key water-borne pathogens. Here, we provide an exhaustive overview of these aptamers and discuss important microbial aspects to consider when developing such aptamers.

A myeloid leukemia factor homolog involved in encystation-induced protein metabolism in Giardia lamblia

BACKGROUND

Giardia lamblia differentiates into resistant cysts as an established model for dormancy. Myeloid leukemia factor (MLF) proteins are important regulators of cell differentiation. Giardia possesses a MLF homolog which was up-regulated during encystation and localized to unknown cytosolic vesicles named MLF vesicles (MLFVs).

METHODS

We used double staining for visualization of potential factors with role in protein metabolism pathway and a strategy that employed a deletion mutant, CDK2m3, to test the protein degradation pathway. We also explored whether autophagy or proteasomal degradation are regulators of Giardia encystation by treatment with MG132, rapamycin, or chloroquine.

RESULTS

Double staining of MLF and ISCU or CWP1 revealed no overlap between their vesicles. The aberrant CDK2m3 colocalized with MLFVs and formed complexes with MLF. MG132 increased the number of CDK2m3-localized vesicles and its protein level. We further found that MLF colocalized and interacted with a FYVE protein and an ATG8-like (ATG8L) protein, which were up-regulated during encystation and their expression induced Giardia encystation. The addition of MG132, rapamycin, or chloroquine, increased their levels and the number of their vesicles, and inhibited the cyst formation. MLF and FYVE were detected in exosomes released from culture.

CONCLUSIONS

The MLFVs are not mitosomes or encystation-specific vesicles, but are related with degradative pathway for CDK2m3. MLF, FYVE, and ATG8L play a positive role in encystation and function in protein clearance pathway, which is important for encystation and coordinated with Exosomes.

GENERAL SIGNIFICANCE

MLF, FYVE, and ATG8L may be involved an encystation-induced protein metabolism during Giardia differentiation.

A Dual Omics Approach to Evaluate Transcriptional and Metabolic Responses During Lipid Deprivation in an Oyster Parasite, Perkinsus marinus

Perkinsus marinus, a protozoan and the causative agent of perkinsosis (dermo disease) is a prevalent parasite found within the eastern oyster (Crassostrea virginica). In this study, we explore metabolic processes of P. marinus cells under lipid-depleted medium conditions to elucidate the interchanging flux of lipid and carbohydrate metabolism. Although P. marinus can synthesize their own lipids from available nutrients, they display a slower growth in medium not supplemented with lipids as opposed to medium with lipids. Under these conditions, using transcriptomics, we surprisingly observed evidence of stimulated lipid degradation through increased transcription of two core β-oxidation pathway enzymes. Simultaneously, phospholipid biosynthetic pathways were downregulated. Metabolomic analysis supported the transcriptomic results. Most fatty acids were decreased in lipid-deplete medium as opposed to lipid-replete medium, and available glucose was fermented to lactate. A significant increase in the cholesterol derivative zymosterol further supported a downregulation of membrane synthesis under the experimental conditions. A robust tricarboxylic acid (TCA) cycle was apparent by enhanced citrate synthase transcription, and a simultaneous reduction in branched chain amino acids. It is concluded that although P. marinus has the capacity for synthesizing its own lipids, it can respond to lipid deprivation in medium by oxidizing readily available stores, and likely transitioning into a resting stage.

A Novel Multiprotein Bridging Factor 1-Like Protein Induces Cyst Wall Protein Gene Expression and Cyst Differentiation in Giardia lamblia

The capacity to synthesize a protective cyst wall is critical for infectivity of Giardia lamblia. It is of interest to know the mechanism of coordinated synthesis of three cyst wall proteins (CWPs) during encystation, a differentiation process. Multiprotein bridging factor 1 (MBF1) gene family is a group of transcription coactivators that bridge various transcription factors. They are involved in cell growth and differentiation in yeast and animals, or in stress response in fungi and plants. We asked whether Giardia has MBF1-like genes and whether their products influence gene expression. BLAST searches of the Giardia genome database identified one gene encoding a putative MBF1 protein with a helix-turn-helix domain. We found that it can specifically bind to the AT-rich initiator promoters of the encystation-induced cwp1-3 and myb2 genes. MBF1 localized to cell nuclei and cytoplasm with higher expression during encystation. In addition, overexpression of MBF1 induced cwp1-3 and myb2 gene expression and cyst generation. Mutation of the helixes in the helix-turn-helix domain reduced cwp1-3 and myb2 gene expression and cyst generation. Chromatin immunoprecipitation assays confirmed the binding of MBF1 to the promoters with its binding sites in vivo. We also found that MBF1 can interact with E2F1, Pax2, WRKY, and Myb2 transcription factors that coordinately up-regulate the cwp genes during encystation. Using a CRISPR/Cas9 system for targeted disruption of mbf1 gene, we found a downregulation of cwp1-3 and myb2 genes and decrease of cyst generation. Our results suggest that MBF1 is functionally conserved and positively regulates Giardia cyst differentiation.

Genome-wide and structural analysis of the Myb-SHAQKYF family in Entamoeba histolytica

Amoebiasis is the third leading cause of death among protozoon parasitic diseases in the lower-middle income countries. Understanding the molecular events that control gene expression such as transcription factors, their DNA binding mode and target sequences can help to develop new antiamoebic drugs against Entamoeba histolytica. In this paper we performed a genome and structural analysis of a specific transcription factor. The genome of E. histolytica codifies for 9 EhMybSHAQKYF proteins, which are a family within a large group of 34 Myb-DNA-binding domain (Myb-DBD) containing proteins. Here we compared Entamoeba Myb-SHAQKYF proteins with Myb-like proteins from the Reveille (RVE) family, important regulators of plant circadian networks. This comparison could lead to stablish their role in E. histolytica life cycle. We show that the ehmybshaqkyf genes are differentially expressed in trophozoites under basal cell culture conditions. An in-silico analysis predicts that members of this group harbor a highly conserved and structured Myb-DBD and a large portion of intrinsically disordered residues. As the Myb-DBD of these proteins harbors a distinctive Q[VI]R[ST]HAQK[YF]F sequence in its putative third α-helix, we consider relevant to determine the three-dimensional (3D) structure of one of them. An NMR structure of the Myb-DBD of EhMybS3 shows that this protein is composed of three α-helices stabilized by a hydrophobic core, similar to Myb proteins of different kingdoms. It is remarkable that despite not sharing similarities in their amino acid sequences, the structure of the Myb-DBD of the EhMybS3 is well conserved in this early branching eukaryote.

Entamoeba histolytica protein CaBP3 uses a calcium dependent nuclear localisation pathway in mammalian cells

Entamoeba histolytica is a major cause of dysentery that leads to a high level of morbidity and mortality, especially in developing countries. Calmodulin-like calcium binding protein EhCaBP3 of E. histolytica is directly involved in disease mechanisms with roles in cytoskeleton dynamics and scission during erythrophagocytosis in a calcium dependent fashion. Interestingly, EhCaBP3 is also present in the nucleus of E. histolytica. We have used a transfected cell system to show that EhCaBP3 is capable of calcium dependent nucleocytoplasmic trafficking. Our data confirms and extends recent findings suggesting presence of a calcium dependent nuclear transport pathway in E. histolytica.

Entamoeba stage conversion: progress and new insights

Entamoeba histolytica, an anaerobic protozoan, is an important global health problem. This parasite has a biphasic life cycle consisting of a dormant cyst stage which is environmentally resistant and transmits the infection, and the proliferative trophozoite stage which is motile and causes invasive disease. The stage conversion process remains poorly understood despite being central to amoebic biology. In this review, we will highlight recent progress in our understanding of Entamoeba stage conversion including dissecting transcriptome analysis in development, characterization of transcriptional networks, demonstration of epigenetic regulation, and role of small molecules that regulate Entamoeba development.

Uncovering the Cyclic AMP Signaling Pathway of the Protozoan Parasite Entamoeba histolytica and Understanding Its Role in Phagocytosis

Second messenger signaling controls a surprisingly diverse range of processes in several eukaryotic pathogens. Molecular machinery and pathways involving these messengers thus hold tremendous opportunities for therapeutic interventions. Relative to Ca²⁺ signaling, the knowledge of a crucial second messenger cyclic AMP (cAMP) and its signaling pathway is very scant in the intestinal parasite Entamoeba histolytica. In the current study, mining the available genomic resources, we have for the first time identified the cAMP signal transduction pathway of E. histolytica. Three heptahelical proteins with variable G-protein-coupled receptor domains, heterotrimeric G-proteins (Gα, Gβ, and Gγ subunits), soluble adenylyl cyclase, cyclase-associated protein, and enzyme carbonic anhydrase were identified in its genome. We could also identify several putative candidate genes for cAMP downstream effectors such as protein kinase A, A-kinase anchoring proteins, and exchange protein directly activated by the cAMP pathway. Using specific inhibitors against key identified targets, we could observe changes in the intracellular cAMP levels as well as defect in the rate of phagocytosis of red blood cells by the parasite E. histolytica. We thus strongly believe that characterization of some of these unexplored crucial signaling determinants will provide a paradigm shift in understanding the pathogenicity of this organism.

A class I histone deacetylase is implicated in the encystation of Entamoeba invadens

Epigenetic mechanisms such as histone acetylation and deacetylation participate in regulation of the genes involved in encystation of Entamoeba invadens. However, the histones and target residues involved, and whether the acetylation and deacetylation of the histones leads to the regulation of gene expression associated with the encystation of this parasite, remain unknown. In this study, we found that E. invadens histone H4 is acetylated in both stages of the parasite and is more highly acetylated during the trophozoite stage than in the cyst. Histone hyperacetylation induced by Trichostatin A negatively affects the encystation of E. invadens, and this inhibition is associated with the downregulation of the expression of genes implicated in the synthesis of chitin, polyamines, gamma-aminobutyric acid pathways and cyst wall proteins, all of which are important in the formation of cysts. Finally, in silico analysis and activity assays suggest that a class I histone deacetylase (EiHDAC3) could be involved in control of the expression of a subset of genes that are important in several pathways during encystation. Therefore, the identification of enzymes that acetylate and/or deacetylate histones that control encystation in E. invadens could be a promising therapeutic target for preventing transmission of other amoebic parasites such as E. histolytica, the causative agent of amoebiasis in humans.

Apparent lack of spill-over of parasites from an invasive anuran: PCR detects Entamoeba in cane toads (Rhinella marina) but not in sympatric Australian native frogs

The recent detection of a novel amoebozoan parasite (Entamoeba sp. CT1) killing invasive cane toads (Rhinella marina) in tropical Australia raises concerns of potential spill-over into native anuran populations. Considering the vulnerability of anuran communities globally, Entamoeba sp. CT1 may pose a serious threat to anuran biodiversity. Through PCR-based detection and molecular identification, we investigated the prevalence of Entamoeba spp. in the faeces and colon tissue of cane toads (Rhinella marina) and eleven native Australian frog species from a single locality in the Northern Territory. No Entamoeba DNA was detected in samples of native frog faeces (N = 57) or colons (N = 17). Entamoeba DNA was detected in 24% of 45 cane toads (95%CI 14.08–38.82). Both E. ranarum and Entamoeba sp. CT1 were present in cane toads. The failure of faecal samples to indicate Entamoeba spp. in infected cane toads may be due to cysts in faeces being shed intermittently, degraded before analysis, or impervious to lysis prior to DNA isolation. Our results suggest that native frogs do not carry the pathogen in an area where 20–30% of cane toads are infected with Entamoeba sp. CT1. We demonstrate the importance of recognising PCR inhibition prior to molecular diagnostics, and the apparent inadequacy of faecal samples for the detection of Entamoeba spp. in anurans.

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Entamoeba spp. were detected in cane toads, but not in faeces or colons of native frogs.

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PCR inhibition of anuran faecal samples.

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Additional purification, the presence of inhibition was reduced.

Averting transmission: A pivotal target to manage amoebiasis

Amoebiasis is a parasitic infectious disease caused by the enteric protozoan Entamoeba histolytica, a leading basis of deaths accounted to parasites, succeeding malaria and schistosomiasis. Conventional treatment methodologies used to deal with amoebiasis mainly rely on the administration of anti-amoebic compounds and vaccines but are often linked with substantial side-effects on the patient. Besides, cases of development of drug resistance in protozoans have been recorded, contributing further to the reduction in the efficiency of the treatment. Loopholes in the efficacious management of the disease call for the development of novel methodologies to manage amoebiasis. A way to achieve this is by targeting the essential metabolic processes of 'encystation' and 'excystation', and the associated biomolecules, thus interrupting the biphasic life cycle of the parasite. Technologies like the CRISPR-Cas9 system can efficiently be exploited to discover novel and essential molecules that regulate the protozoan's metabolism, while efficiently manipulating and managing the known drug targets, leading to an effective halt and forestall to the enteric infection. This review presents a perspective on these essential metabolic processes and the associated molecules that can be targeted efficaciously to prevent the transmission of amoebiasis, thus managing the disease and proving to be a fruitful endeavour.

Novel insights into molecular mechanisms of Pseudourostyla cristata encystment using comparative transcriptomics

The encystment of many ciliates is an advanced survival strategy against adversity and the most important reason for ciliates existence worldwide. However, the molecular mechanism for the encystment of free-living ciliates is poorly understood. Here, we performed comparative transcriptomic analysis of dormant cysts and trophonts from Pseudourostyla cristata using transcriptomics, qRT-PCR and bioinformatic techniques. We identified 2565 differentially expressed unigenes between the dormant cysts and the trophonts. The total number of differentially expressed genes in GO database was 1752. The differential unigenes noted to the GO terms were 1993. These differential categories were mainly related to polyamine transport, pectin decomposition, cytoplasmic translation, ribosome, respiratory chain, ribosome structure, ion channel activity, and RNA ligation. A total of 224 different pathways were mapped. Among them, 184 pathways were upregulated, while 162 were downregulated. Further investigation showed that the calcium and AMPK signaling pathway had important induction effects on the encystment. In addition, FOXO and ubiquitin-mediated proteolysis signaling pathway jointly regulated the encystment. Based on these findings, we propose a hypothetical signaling network that regulates Pseudourostyla cristata encystment. Overall, these results provide deeper insights into the molecular mechanisms of ciliates encystment and adaptation to adverse environments.

Glycogen synthase kinase 3 promotes multicellular development over unicellular encystation in encysting Dictyostelia

BACKGROUND

Glycogen synthase kinase 3 (GSK3) regulates many cell fate decisions in animal development. In multicellular structures of the group 4 dictyostelid Dictyostelium discoideum, GSK3 promotes spore over stalk-like differentiation. We investigated whether, similar to other sporulation-inducing genes such as cAMP-dependent protein kinase (PKA), this role of GSK3 is derived from an ancestral role in encystation of unicellular amoebas.

RESULTS

We deleted GSK3 in Polysphondylium pallidum, a group 2 dictyostelid which has retained encystation as an alternative survival strategy. Loss of GSK3 inhibited cytokinesis of cells in suspension, as also occurs in D. discoideum, but did not affect spore or stalk differentiation in P. pallidum. However, gsk3^- amoebas entered into encystation under conditions that in wild type favour aggregation and fruiting body formation. The gsk3^- cells were hypersensitive to osmolytes, which are known to promote encystation, and to cyst-inducing factors that are secreted during starvation. GSK3 was not itself regulated by these factors, but inhibited their effects.

CONCLUSIONS

Our data show that GSK3 has a deeply conserved role in controlling cytokinesis, but not spore differentiation in Dictyostelia. Instead, in P. pallidum, one of many Dictyostelia that like their solitary ancestors can still encyst to survive starvation, GSK3 promotes multicellular development into fruiting bodies over unicellular encystment.

Encystation: the most prevalent and underinvestigated differentiation pathway of eukaryotes

Not long ago, protists were considered one of four eukaryote kingdoms, but recent gene-based phylogenies show that they contribute to all nine eukaryote subdomains. The former kingdoms of animals, plants and fungi are now relegated to lower ranks within subdomains. Most unicellular protists respond to adverse conditions by differentiating into dormant walled cysts. As cysts, they survive long periods of starvation, drought and other environmental threats, only to re-emerge when conditions improve. For protists pathogens, the resilience of their cysts can prevent successful treatment or eradication of the disease. In this context, effort has been directed towards understanding the molecular mechanisms that control encystation. We here firstly summarize the prevalence of encystation across protists and next focus on Amoebozoa, where most of the health-related issues occur. We review current data on processes and genes involved in encystation of the obligate parasite Entamoeba histolytica and the opportunistic pathogen Acanthamoeba. We show how the cAMP-mediated signalling pathway that controls spore and stalk cell encapsulation in Dictyostelium fruiting bodies could be retraced to a stress-induced pathway controlling encystation in solitary Amoebozoa. We highlight the conservation and prevalence of cAMP signalling genes in Amoebozoan genomes and the suprisingly large and varied repertoire of proteins for sensing and processing environmental signals in individual species.

Nuclear transport in Entamoeba histolytica: knowledge gap and therapeutic potential

Entamoeba histolytica is the protozoan parasite that causes human amoebiasis. It is one of the leading parasitic disease burdens in tropical regions and developing countries, with spread to developed countries through migrants from and travellers to endemic regions.Understanding E. histolytica's invasion mechanisms requires an understanding of how it interacts with external cell components and how it engulfs and kills cells (phagocytosis). Recent research suggests that optimal phagocytosis requires signalling events from the cell surface to the nucleus via the cytoplasm, and the induction of several factors that are transported to the plasma membrane. Current research in other protozoans suggests the presence of proteins with nuclear localization signals, nuclear export signals and Ran proteins; however, there is limited literature on their functionality and their functional similarity to higher eukaryotes.Based on learnings from the development of antivirals, nuclear transport elements in E. histolytica may present viable, specific, therapeutic targets.In this review, we aim to summarize our limited knowledge of the eukaryotic nuclear transport mechanisms that are conserved and may function in E. histolytica.

What Kills the Hindgut Flagellates of Lower Termites during the Host Molting Cycle?

Subsocial wood feeding cockroaches in the genus Cryptocercus, the sister group of termites, retain their symbiotic gut flagellates during the host molting cycle, but in lower termites, closely related flagellates die prior to host ecdysis. Although the prevalent view is that termite flagellates die because of conditions of starvation and desiccation in the gut during the host molting cycle, the work of L.R. Cleveland in the 1930s through the 1960s provides a strong alternate hypothesis: it was the changed hormonal environment associated with the origin of eusociality and its concomitant shift in termite developmental ontogeny that instigates the death of the flagellates in termites. Although the research on termite gut microbial communities has exploded since the advent of modern molecular techniques, the role of the host hormonal environment on the life cycle of its gut flagellates has been neglected. Here Cleveland's studies are revisited to provide a basis for re-examination of the problem, and the results framed in the context of two alternate hypotheses: the flagellate symbionts are victims of the change in host social status, or the flagellates have become incorporated into the life cycle of the eusocial termite colony. Recent work on parasitic protists suggests clear paths for exploring these hypotheses and for resolving long standing issues regarding sexual-encystment cycles in flagellates of the Cryptocercus-termite lineage using molecular methodologies, bringing the problem into the modern era.

Ultrastructural features of the tomont of Cryptocaryon irritans (Ciliophora: Prostomatea), a parasitic ciliate of marine fishes

Numerous studies have been conducted on the cellular morphology of Cryptocaryon irritans. However, details regarding the tomont stage of its life cycle remain lacking. In this study, we investigated the morphology of the tomont stage throughout encystment and cell division using light and electron microscopy. Results showed that there was no secretion of encystation-specific secretory vesicles or extrusomes during formation of the cyst wall. Instead, the synthesis and construction of the C. irritans cyst wall materials may involve molecular events at the pellicle. The somatic cilia and the cytostome were present during encystment and covered by the newly formed cyst wall. New somatic cilia were continuously created between old cilia and showed various lengths during cell division, a process that was similar to morphogenesis in many free-living ciliates. During cell division inside the tomont, dividing daughter cells formed temporary cell chains with no oral primordia before separating from each other into dissociative tomite precursors. The process of cell division may not be accompanied by stomatogenesis, and new oral primordia in offspring cells likely formed before the dividing cell chains split into dissociative spherical tomites. Mitochondrial autophagy was observed in encysting C. irritans cells. Numerous endosymbionts and Golgi structures were observed in the tomont cytoplasm. Cellular metabolic activity in the C. irritans tomont was quite high, with large amounts of materials or cellular organelles potentially being synthesized and prepared for the following infective theront stage.

Nanomaterials-based biosensors for detection of microorganisms and microbial toxins

Detection of microorganisms and microbial toxins is important for health and safety. Due to their unique physical and chemical properties, nanomaterials have been extensively used to develop biosensors for rapid detection of microorganisms with microbial cells and toxins as target analytes. In this paper, the design principles of nanomaterials-based biosensors for four selected analyte categories (bacteria cells, toxins, mycotoxins, and protozoa cells), closely associated with the target analytes' properties is reviewed. Five signal transducing methods that are less equipment intensive (colorimetric, fluorimetric, surface enhanced Raman scattering, electrochemical, and magnetic relaxometry methods) is described and compared for their sensory performance (in term oflimit of detection, dynamic range, and response time) for all analyte categories. In the end, the suitability of these five sensing principles for on-site or field applications is discussed. With a comprehensive coverage of nanomaterials, design principles, sensing principles, and assessment on the sensory performance and suitability for on-site application, this review offers valuable insight and perspective for designing suitable nanomaterials-based microorganism biosensors for a given application.

Entamoeba Encystation: New Targets to Prevent the Transmission of Amebiasis

Amebiasis is caused by Entamoeba histolytica infection and can produce a broad range of clinical signs, from asymptomatic cases to patients with obvious symptoms. The current epidemiological and clinical statuses of amebiasis make it a serious public health problem worldwide. The Entamoeba life cycle consists of the trophozoite, the causative agent for amebiasis, and the cyst, the form responsible for transmission. These two stages are connected by "encystation" and "excystation." Hence, developing novel strategies to control encystation and excystation will potentially lead to new measures to block the transmission of amebiasis by interrupting the life cycle of the causative agent. Here, we highlight studies investigating encystation using inhibitory chemicals and categorize them based on the molecules inhibited. We also present a perspective on new strategies to prevent the transmission of amebiasis.

Activity, stability and folding analysis of the chitinase from Entamoeba histolytica

Human amebiasis, caused by the parasitic protozoan Entamoeba histolytica, remains as a significant public health issue in developing countries. The life cycle of the parasite compromises two main stages, trophozoite and cyst, linked by two major events: encystation and excystation. Interestingly, the cyst stage has a chitin wall that helps the parasite to withstand harsh environmental conditions. Since the amebic chitinase, EhCHT1, has been recognized as a key player in both encystation and excystation, it is plausible to consider that specific inhibition could arrest the life cycle of the parasite and, thus, stop the infection. However, to selectively target EhCHT1 it is important to recognize its unique biochemical features to have the ability to control its cellular function. Hence, to gain further insights into the structure-function relationship, we conducted an experimental approach to examine the effects of pH, temperature, and denaturant concentration on the enzymatic activity and protein stability. Additionally, dependence on in vivo oxidative folding was further studied using a bacterial model. Our results attest the potential of EhCHT1 as a target for the design and development of new or improved anti-amebic therapeutics. Likewise, the potential of the oxidoreductase EhPDI, involved in oxidative folding of amebic proteins, was also confirmed.

Heat Shock Protein 90 regulates encystation in Entamoeba

Enteric protozoan Entamoeba histolytica is a major cause of debilitating diarrheal infection worldwide with high morbidity and mortality. Even though the clinical burden of this parasite is very high, this infection is categorized as a neglected disease. Parasite is transmitted through feco-oral route and exhibit two distinct stages namely – trophozoites and cysts. Mechanism and regulation of encystation is not clearly understood. Previous studies have established the role of Heat shock protein 90 (Hsp90) in regulating stage transition in various protozoan parasites like Giardia, Plasmodium, Leishmania, and Toxoplasma. Our study for the first time reports that Hsp90 plays a crucial role in life cycle of Entamoeba as well. We identify Hsp90 to be a negative regulator of encystation in Entamoeba. We also show that Hsp90 inhibition interferes with the process of phagocytosis in Entamoeba. Overall, we show that Hsp90 plays an important role in virulence and transmission of Entamoeba.

Ethanol and isopropanol in concentrations present in hand sanitizers sharply reduce excystation of Giardia and Entamoeba and eliminate oral infectivity of Giardia cysts in gerbils

Enteric protozoan parasites, which are spread by the fecal-oral route, are important causes of diarrhea (Giardia duodenalis) and amebic dysentery (Entamoeba histolytica). Cyst walls of Giardia and Entamoeba have a single layer composed of fibrils of β-1,3-linked GalNAc and β-1,4-linked GlcNAc (chitin), respectively. The goal here was to determine whether hand sanitizers that contain ethanol or isopropanol as the active microbicide might reduce transmission of these parasites. We found that treatment with these alcohols with or without drying in a rotary evaporator (to model rapid evaporation of sanitizers on hands) kills 85 to 100% of cysts of G. duodenalis and 90 to 100% of cysts of Entamoeba invadens (a nonpathogenic model for E. histolytica), as shown by nuclear labeling with propidium iodide and failure to excyst in vitro. Alcohols with or without drying collapsed the cyst walls of Giardia but did not collapse the cyst walls of Entamoeba. To validate the in vitro results, we showed that treatment with alcohols eliminated oral infection of gerbils by 1,000 G. duodenalis cysts, while a commercial hand sanitizer (Purell) killed E. invadens cysts that were directly applied to the hands. These results suggest that expanded use of alcohol-based hand sanitizers might reduce the transmission of Giardia and Entamoeba.

Entamoeba mitosomes play an important role in encystation by association with cholesteryl sulfate synthesis

Hydrogenosomes and mitosomes are mitochondrion-related organelles (MROs) that have highly reduced and divergent functions in anaerobic/microaerophilic eukaryotes. Entamoeba histolytica, a microaerophilic, parasitic amoebozoan species, which causes intestinal and extraintestinal amoebiasis in humans, possesses mitosomes, the existence and biological functions of which have been a longstanding enigma in the evolution of mitochondria. We previously demonstrated that sulfate activation, which is not generally compartmentalized to mitochondria, is a major function of E. histolytica mitosomes. However, because the final metabolites of sulfate activation remain unknown, the overall scheme of this metabolism and the role of mitosomes in Entamoeba have not been elucidated. In this study we purified and identified cholesteryl sulfate (CS) as a final metabolite of sulfate activation. We then identified the gene encoding the cholesteryl sulfotransferase responsible for synthesizing CS. Addition of CS to culture media increased the number of cysts, the dormant form that differentiates from proliferative trophozoites. Conversely, chlorate, a selective inhibitor of the first enzyme in the sulfate-activation pathway, inhibited cyst formation in a dose-dependent manner. These results indicate that CS plays an important role in differentiation, an essential process for the transmission of Entamoeba between hosts. Furthermore, we show that Mastigamoeba balamuthi, an anaerobic, free-living amoebozoan species, which is a close relative of E. histolytica, also has the sulfate-activation pathway in MROs but does not possess the capacity for CS production. Hence, we propose that a unique function of MROs in Entamoeba contributes to its adaptation to its parasitic life cycle.

Stress management in cyst-forming free-living protists: programmed cell death and/or encystment

In the face of harsh conditions and given a choice, a cell may (i) undergo programmed cell death, (ii) transform into a cancer cell, or (iii) enclose itself into a cyst form. In metazoans, the available evidence suggests that cellular machinery exists only to execute or avoid programmed cell death, while the ability to form a cyst was either lost or never developed. For cyst-forming free-living protists, here we pose the question whether the ability to encyst was gained at the expense of the programmed cell death or both functions coexist to counter unfavorable environmental conditions with mutually exclusive phenotypes.

Heterogeneity of quaternary structure of glucosamine-6-phosphate deaminase from Giardia lamblia

The oligoHis-tagged versions of glucosamine-6-phosphate deaminase from Giardia lamblia (GlmNagB-HisN, GlmNagB-HisC) were constructed and purified to hear homogeneity, and their kinetic and structural properties were compared to those of the wild-type enzyme (GlmNagB). Introduction of the oligoHis tag at the GlmNagB C-terminus resulted in almost complete loss of the catalytic activity, while the catalytic properties of GlmNagB-HisN and GlmNagB were very similar. The recombinant and wild-type enzyme exhibits heterogeneity of the quaternary structure and in solution exists in three interconvertible forms, namely, monomeric, homodimeric, and homotetrameric. Although the monomeric form is prevalent, the monomer/dimer/tetramer ratios depended on protein concentration and fell within the range from 72:27:1 to 39:23:38. The enzyme is fully active in each of the oligomeric structures, efficiently catalyzes synthesis of D-glucosamine-6-phosphate from D-fructose-6-phosphate and ammonia, and its activity is not modified by GlcNAc6P, UDP-GlcNAc, or UDP-GalNAc. GlcN6P deaminase of G. lamblia represents a novel structural and functional type of enzyme of the NagB subfamily.

Proteomic approach to reveal the proteins associated with encystment of the ciliate Euplotes encysticus

In order to identify and reveal the proteins related to encystment of the ciliate Euplotes encysticus, we analyzed variation in the abundance of the proteins isolated from the resting cyst comparing with proteins in the vegetative cell. 2-D electrophoresis, MALDI-TOF MS techniques and Bioinformatics were used for proteome separation, quantification and identification. The comparative proteomics studies revealed 26 proteins with changes on the expression in the resting cysts, including 12 specific proteins and 14 differential proteins. 12 specific proteins and 10 out of the 14 differential proteins were selected and identified by MALDI-TOF MS. The identified specific proteins with known functions included type II cytoskeletal 1, keratin, Nop16 domain containing protein, protein arginine n-methyltransferase, epsilon-trimethyllysine hydroxylase and calpain-like protein. The identified differential proteins with known functions included Lysozyme C, keratinocyte growth factor, lysozyme homolog AT-2, formate acetyltransferase, alpha S1 casein and cold-shock protein. We discussed the functions of these proteins as well as their contribution in the process of encystment. These identified proteins covered a wide range of molecular functions, including gene regulation, RNA regulation, proteins degradation and oxidation resistance, stress response, material transport and cytoskeleton organization. Therefore, differential expression of these proteins was essential for cell morphological and physiological changes during encystment. This suggested that the peculiar proteins and differential proteins might play important roles in the process of the vegetative cells transforming into the resting cysts. These observations may be novel findings that bring new insights into the detailed mechanisms of dormancy.

Encystment in Acanthamoeba castellanii: a review

Differentiation of Acanthamoeba castellanii trophozoites involves massive turnover of cellular components and remodelling of organelle structure and function so as to produce a cryptobiotic cell, resistant to desiccation, heat, freezing, and chemical treatments. This review presents a summary of a decade of research on the most studied aspects of the biochemistry of this process, with emphasis on problems of biocide and drug resistances, putative new targets, molecular and cell biology of the process of encystment, and the characteristics of the encysted state. As well as the intrinsic pathogenicity of the organism towards the cornea, and the ability of related species to invade the human brain, its propensity for harbouring and transmitting pathogenic bacteria and viruses is considerable and leads to increasing concerns. The long-term survival and resistance of cysts to drugs and biocides adds another layer of complexity to the problem of their elimination.

The genome and transcriptome of the enteric parasite Entamoeba invadens, a model for encystation

Background

Several eukaryotic parasites form cysts that transmit infection. The process is found in diverse organisms such as Toxoplasma, Giardia, and nematodes. In Entamoeba histolytica this process cannot be induced in vitro, making it difficult to study. In Entamoeba invadens, stage conversion can be induced, but its utility as a model system to study developmental biology has been limited by a lack of genomic resources. We carried out genome and transcriptome sequencing of E. invadens to identify molecular processes involved in stage conversion.

Results

We report the sequencing and assembly of the E. invadens genome and use whole transcriptome sequencing to characterize changes in gene expression during encystation and excystation. The E. invadens genome is larger than that of E. histolytica, apparently largely due to expansion of intergenic regions; overall gene number and the machinery for gene regulation are conserved between the species. Over half the genes are regulated during the switch between morphological forms and a key signaling molecule, phospholipase D, appears to regulate encystation. We provide evidence for the occurrence of meiosis during encystation, suggesting that stage conversion may play a key role in recombination between strains.

Conclusions

Our analysis demonstrates that a number of core processes are common to encystation between distantly related parasites, including meiosis, lipid signaling and RNA modification. These data provide a foundation for understanding the developmental cascade in the important human pathogen E. histolytica and highlight conserved processes more widely relevant in enteric pathogens.

Inactivation of exogenous endoparasite stages by chemical disinfectants: current state and perspectives

Chemical disinfection is common practice and inevitable to achieve sufficient control over parasites particularly in intensive animal housing systems. To identify suitable chemicals, reliable data on antiparasitic efficacy of disinfectants are required. This review summarizes recently published experience with procedures applied to evaluate the viability of a variety of endoparasites following physical or chemical stress. It is concluded that laboratory models used to assess antiparasitic efficacy of e.g. commercial disinfectants should consider the most resistant stages of both helminths and protozoa, i.e. ascarid eggs and coccidia oocysts. To ensure reproducibility and transparency, standardized protocols are pivotal. Such protocols are established on a national level (e.g. DVG guidelines in Germany); however, internationally accepted certification procedures are currently lacking.

Killing the dead: chemotherapeutic strategies against free-living cyst-forming protists (Acanthamoeba sp. and Balamuthia mandrillaris)

The opportunist free-living protists such as Acanthamoeba spp. and Balamuthia mandrillaris have become a serious threat to human life. As most available drugs target functional aspects of pathogens, the ability of free-living protists to transform into metabolically inactive cyst forms presents a challenge in treatment. It is hoped, that the development of broad spectrum antiprotist agents acting against multiple cyst-forming protists to provide target-directed inhibition will offer a viable drug strategy in the treatment of these rare infections. Here, we present a comprehensive report on upcoming drug targets, with emphasis on cyst wall biosynthesis along with the related biochemistry of encystment pathways, as we strive to bring ourselves a step closer to being able to combat these deadly diseases.

Silencing of Entamoeba histolytica glucosamine 6-phosphate isomerase by RNA interference inhibits the formation of cyst-like structures

Encystment is an essential process in the biological cycle of the human parasite Entamoeba histolytica. In the present study, we evaluated the participation of E. histolytica Gln6Pi in the formation of amoeba cyst-like structures by RNA interference assay. Amoeba trophozoites transfected with two Gln6Pi siRNAs reduced the expression of the enzyme in 85%, which was confirmed by western blot using an anti-Gln6Pi antibody. The E. histolytica Gln6Pi knockdown with the mix of both siRNAs resulted in the loss of its capacity to form cyst-like structures (CLSs) and develop a chitin wall under hydrogen peroxide treatment, as evidenced by absence of both resistance to detergent treatment and calcofluor staining. Thus, only 5% of treated trophozoites were converted to CLS, from which only 15% were calcofluor stained. These results represent an advance in the understanding of chitin biosynthesis in E. histolytica and provide insight into the encystment process in this parasite, which could allow for the developing of new control strategies for this parasite.

RNA-seq-based metatranscriptomic and microscopic investigation reveals novel metalloproteases of Neobodo sp. as potential virulence factors for soft tunic syndrome in Halocynthia roretzi

Bodonids and trypanosomatids are derived from a common ancestor with the bodonids being a more primitive lineage. The Neobodonida, one of the three clades of bodonids, can be free-living, commensal or parasitic. Despite the ecological and evolutionary significance of these organisms, however, many of their biological and pathological features are currently unknown. Here, we employed metatranscriptomics using RNA-seq technology combined with field-emission microscopy to reveal the virulence factors of a recently described genus of Neobodonida that is considered to be responsible for ascidian soft tunic syndrome (AsSTS), but whose pathogenesis is unclear. Our microscopic observation of infected tunic tissues suggested putative virulence factors, enabling us to extract novel candidate transcripts; these included cysteine proteases of the families C1 and C2, serine proteases of S51 and S9 families, and metalloproteases grouped into families M1, M3, M8, M14, M16, M17, M24, M41, and M49. Protease activity/inhibition assays and the estimation of expression levels within gene clusters allowed us to identify metalloprotease-like enzymes as potential virulence attributes for AsSTS. Furthermore, a multimarker-based phylogenetic analysis using 1,184 concatenated amino acid sequences clarified the order Neobodo sp. In sum, we herein used metatranscriptomics to elucidate the in situ expression profiles of uncharacterized putative transcripts of Neobodo sp., combined these results with microscopic observation to select candidate genes relevant to pathogenesis, and used empirical screening to define important virulence factors.

Chitinase dependent control of protozoan cyst burden in the brain

Chronic infections represent a continuous battle between the host's immune system and pathogen replication. Many protozoan parasites have evolved a cyst lifecycle stage that provides it with increased protection from environmental degradation as well as endogenous host mechanisms of attack. In the case of Toxoplasma gondii, these cysts are predominantly found in the immune protected brain making clearance of the parasite more difficult and resulting in a lifelong infection. Currently, little is known about the nature of the immune response stimulated by the presence of these cysts or how they are able to propagate. Here we establish a novel chitinase-dependent mechanism of cyst control in the infected brain. Despite a dominant Th1 immune response during Toxoplasma infection there exists a population of alternatively activated macrophages (AAMØ) in the infected CNS. These cells are capable of cyst lysis via the production of AMCase as revealed by live imaging, and this chitinase is necessary for protective immunity within the CNS. These data demonstrate chitinase activity in the brain in response to a protozoan pathogen and provide a novel mechanism to facilitate cyst clearance during chronic infections.

Described here is a novel mechanism of protozoan cyst clearance in the CNS during chronic infection. These data show the presence of a population of alternatively activated macrophages in the brain that secrete the active chitinase, AMCase, in response to chitin in the cyst wall. Using both chemical and genetic inhibition in vitro, it is revealed that this enzyme is required for efficient degradation and destruction of the cyst. The necessity for AMCase is demonstrated in vivo, as the absence of the enzyme resulted in a significant increase in cyst burden and decrease in survival during chronic infection. Together, these data identify an important mechanism of parasite control and cyst clearance in the CNS. Currently, no therapies exist that lead to the total clearance of this parasite from the brain. Therefore, developing an understanding of the natural mechanisms of cyst clearance has the potential to lead to new and effective therapies for this and other chronic infections.