Tunic extract of the host ascidian attracts the causal agent of soft tunic syndrome, Azumiobodo hoyamushi (Kinetoplastea: Neobodonida)

Azumiobodo hoyamushi, a kinetoplastid flagellate, is the causative agent of soft tunic syndrome, an infectious disease of the edible ascidian Halocynthia roretzi. The flagellate is thought to invade the tunic matrix via a damaged area of the tunic on the siphon wall. We hypothesized that the flagellate locates the tunic entry site by a chemotactic response to soluble substances diffused from the host ascidians. To investigate this hypothesis, we examined whether the flagellate shows a chemotactic response to tissue extracts (tunic and other tissues) from the host ascidian H. roretzi. We tested extracts from 5 tissues as well as hemolymph. Only the tunic extract showed significant positive chemotactic activity, and the activity decreased with increasing dilution. Furthermore, autoclaved tunic extract, extracts from diseased individuals, and extract from the styelid ascidian Styela clava also had chemotactic activity, although the activities were lower than that of tunic extract from healthy H. roretzi. Ultrafiltration of the tunic extract through a 3 kDa cutoff membrane completely abrogated the activity; the ultrafiltration retentate still showed activity. Thus, the soluble factors that attract the flagellate are present exclusively in the tunic extract, and the chemotactic factors are larger than 3 kDa. Our experiments also suggested that the tunic extract contains both heat-stable and heat-labile factors. We conclude that the flagellate locates the tunic entry site by chemotaxis toward soluble factors that diffuse from a damaged area of the tunic on the siphon wall.

Feeding and growth of the marine heterotrophic nanoflagellates, Procryptobia sorokini and Paraphysomonas imperforata on a bacterium, Pseudoalteromonas sp. with an inducible defence against grazing

Heterotrophic marine nanoflagellates are important grazers on bacteria in the water column. Some marine bacteria appear more resistant to grazing than do others. Marine nanoflagellates can be grown in the laboratory in batch cultures fed specific bacterial isolates. In some cultures, the flagellates appear unable to completely deplete the bacterial prey even when the bacterial strain otherwise is an excellent prey. This may indicate that some marine bacteria are able to induce defence mechanisms if they are grazed by nanoflagellates. Four morphologically distinct marine heterotrophic nanoflagellates, of which 3 were still identified as Procryptobia sorokini (Kinetoplastea) and one as Paraphysomonas imperforata (Chrysophyceae) were isolated from a coastal location along with 3 isolates of the marine bacterium Pseudoalteromonas sp. Flagellate growth and grazing on bacterial prey were analysed in batch cultures. Pseudoalteromonas was a suitable prey for all 4 flagellate isolates. They grazed and grew on Pseudoalteromonas as sole prey with maximal cell-specific growth rates of 0.1–0.25 h^-1 and gross growth efficiencies of 38–61%. Exposure to dense flagellate cultures or their supernatants did, however, cause a fraction of the Pseudoalteromonas cells to aggregate and the bacterium became apparently resistant to grazing. Concentrations of suspended Pseudoalteromonas cells were therefore not decreased below 1,700–7,500 cells μL^-1 by any of the flagellate isolates. These results indicate that Pseudoalteromonas sp. can be an excellent prey to marine nanoflagellates but also that is in possession of inducible mechanisms that protect against flagellate grazing.

Novel scaffolds for inhibition of Cruzipain identified from high-throughput screening of anti-kinetoplastid chemical boxes

American Trypanosomiasis or Chagas disease is a prevalent, neglected and serious debilitating illness caused by the kinetoplastid protozoan parasite Trypanosoma cruzi. The current chemotherapy is limited only to nifurtimox and benznidazole, two drugs that have poor efficacy in the chronic phase and are rather toxic. In this scenario, more efficacious and safer drugs, preferentially acting through a different mechanism of action and directed against novel targets, are particularly welcome. Cruzipain, the main papain-like cysteine peptidase of T. cruzi, is an important virulence factor and a chemotherapeutic target with excellent pre-clinical validation evidence. Here, we present the identification of new Cruzipain inhibitory scaffolds within the GlaxoSmithKline HAT (Human African Trypanosomiasis) and Chagas chemical boxes, two collections grouping 404 non-cytotoxic compounds with high antiparasitic potency, drug-likeness, structural diversity and scientific novelty. We have adapted a continuous enzymatic assay to a medium-throughput format and carried out a primary screening of both collections, followed by construction and analysis of dose-response curves of the most promising hits. Using the identified compounds as a starting point a substructure directed search against CHEMBL Database revealed plausible common scaffolds while docking experiments predicted binding poses and specific interactions between Cruzipain and the novel inhibitors.

Isolation of Novel Trypanosomatid, Zelonia australiensis sp. nov. (Kinetoplastida: Trypanosomatidae) Provides Support for a Gondwanan Origin of Dixenous Parasitism in the Leishmaniinae

The genus Leishmania includes approximately 53 species, 20 of which cause human leishmaniais; a significant albeit neglected tropical disease. Leishmaniasis has afflicted humans for millennia, but how ancient is Leishmania and where did it arise? These questions have been hotly debated for decades and several theories have been proposed. One theory suggests Leishmania originated in the Palearctic, and dispersed to the New World via the Bering land bridge. Others propose that Leishmania evolved in the Neotropics. The Multiple Origins theory suggests that separation of certain Old World and New World species occurred due to the opening of the Atlantic Ocean. Some suggest that the ancestor of the dixenous genera Leishmania, Endotrypanum and Porcisia evolved on Gondwana between 90 and 140 million years ago. In the present study a detailed molecular and morphological characterisation was performed on a novel Australian trypanosomatid following its isolation in Australia’s tropics from the native black fly, Simulium (Morops) dycei Colbo, 1976. Phylogenetic analyses were conducted and confirmed this parasite as a sibling to Zelonia costaricensis, a close relative of Leishmania previously isolated from a reduviid bug in Costa Rica. Consequently, this parasite was assigned the name Zelonia australiensis sp. nov. Assuming Z. costaricensis and Z. australiensis diverged when Australia and South America became completely separated, their divergence occurred between 36 and 41 million years ago at least. Using this vicariance event as a calibration point for a phylogenetic time tree, the common ancestor of the dixenous genera Leishmania, Endotrypanum and Porcisia appeared in Gondwana approximately 91 million years ago. Ultimately, this study contributes to our understanding of trypanosomatid diversity, and of Leishmania origins by providing support for a Gondwanan origin of dixenous parasitism in the Leishmaniinae.

The genus Leishmania includes approximately 53 species, 20 of which cause human leishmaniais, a significant disease that has afflicted humans for millennia. But how ancient is Leishmania and where did it arise? Some suggest Leishmania originated in the Palearctic. Others suggest it appeared in the Neotropics. The Multiple Origins theory proposes that separation of certain Old World and Neotropical species occurred following the opening of the Atlantic. Others suggest that an ancestor to the Euleishmania and Paraleishmania appeared on Gondwana 90 to 140 million years ago (MYA). We performed a detailed molecular and morphological characterisation of a novel Australian trypanosomatid. This parasite is a sibling to the Neotropical Zelonia costaricensis, a close relative of Leishmania, and designated as Zelonia australiensis sp. nov. Assuming Z. costaricensis and Z. australiensis split when Australia and South America separated, their divergence occurred between 36 and 41 MYA. Using this event as a calibration point for a phylogenetic time tree, an ancestor of the dixenous Leishmaniinae appeared in Gondwana ~ 91 MYA. This study contributes to our understanding of trypanosomatid diversity by describing a unique Australian trypanosomatid and to our understanding of Leishmania evolution by inferring a Gondwanan origin for dixenous parasitism in the Leishmaniinae.

Disinfection of fertilized eggs of the edible ascidian Halocynthia roretzi for prevention of soft tunic syndrome

Azumiobodo hoyamushi, the causative agent of soft tunic syndrome, was likely introduced to farming sites of the edible ascidian Halocynthia roretzi via ascidian spat. The source of infection is thought to be cysts of A. hoyamushi that reside in the substrates on which the ascidian spat are attached, but not the spat themselves. Thus, there is a need to develop methods to prevent contamination of the substrates with A. hoyamushi during seed production of the ascidian. We evaluated the protozoacidal effects of sodium hypochlorite and povidone-iodine against the flagellate and temporary cyst forms of A. hoyamushi. Additionally, we evaluated the effects of these disinfectants on the development of fertilized ascidian eggs. The flagellate form of A. hoyamushi was completely inactivated by povidone-iodine (5 ppm, 1 min) and sodium hypochlorite (1 ppm, 1 min). The temporary cysts of A. hoyamushi were completely inactivated by both disinfectants (5 ppm, 1 min). Disinfection with 50 ppm povidone-iodine for 15 min or 5 ppm sodium hypochlorite for 15 min had no effect on ascidian embryogenesis. Thus, horizontal transmission of A. hoyamushi via the substrates can be efficiently prevented by disinfecting ascidian eggs or tools used for spawning with povidone-iodine baths ranging from 5 ppm for 1 min to 50 ppm for 15 min without any side effects.

Cellulose is not degraded in the tunic of the edible ascidian Halocynthia roretzi contracting soft tunic syndrome

Soft tunic syndrome is a fatal disease in the edible ascidian Halocynthia roretzi, causing serious damage to ascidian aquaculture in Korea and Japan. In diseased individuals, the tunic, an integumentary extracellular matrix of ascidians, softens and eventually tears. This is an infectious disease caused by the kinetoplastid flagellate Azumiobodo hoyamushi. However, the mechanism of tunic softening remains unknown. Because cellulose fibrils are the main component of the tunic, we compared the contents and structures of cellulose in healthy and diseased tunics by means of biochemical quantification and X-ray diffractometry. Unexpectedly, the cellulose contents and structures of cellulose microfibrils were almost the same regardless of the presence or absence of the disease. Therefore, it is unlikely that thinning of the microfibrils occurred in the softened tunic, because digestion should have resulted in decreases in crystallinity index and crystallite size. Moreover, cellulase was not detected in pure cultures of A. hoyamushi in biochemical and expressed sequence tag analyses. These results indicate that cellulose degradation does not occur in the softened tunic.

Encystment and excystment of kinetoplastid Azumiobodo hoyamushi, causal agent of soft tunic syndrome in ascidian aquaculture

Soft tunic syndrome in the edible ascidian Halocynthia roretzi is caused by the kinetoplastid flagellate Azumiobodo hoyamushi, which was found to assume a fusiform cell form with 2 flagella in axenic, pure culture. When the flagellate form was incubated in sterilized artificial seawater (pH 8.4), some of the cells became cyst-like and adhered to the bottom of the culture plate. The cyst-like forms were spherical or cuboidal, and each had 2 flagella encapsulated in its cytoplasm. Encystment was also induced in culture medium alkalified to the pH of seawater (8.4) but not in unmodified (pH 7.2) or acidified media (pH 6.4). More than 95% of the cyst-like cells converted to the flagellate form within 1 d following transfer to seawater containing ascidian tunic extracts from host ascidians. The cyst-like cells were able to survive in seawater with no added nutrients for up to 2 wk at 20°C and for a few months at 5 to 15°C. The survival period in seawater depended on temperature: some cyst-like cells survived 3 mo at 10°C, and ca. 95% of these converted to flagellate forms in seawater containing tunic extracts. Thus, A. hoyamushi is able to persist under adverse conditions in a cyst-like form able to adhere to organic and inorganic substrata for protracted periods of time.

Epidermal response of rainbow trout to Ichthyobodo necator: immunohistochemical and gene expression studies indicate a Th1-/Th2-like switch

Infections with the parasitic flagellate Ichthyobodo necator (Henneguy, 1883) cause severe skin and gill disease in rainbow trout Oncorhynchus mykiss (Walbaum, 1792) juveniles. The epidermal disturbances including hyperplasia and mucous cell exhaustion caused by parasitization are known, but no details on specific cellular and humoral reactions have been presented. By applying gene expression methods and immunohistochemical techniques, further details of immune processes in the affected skin can be presented. A population of I. necator was established in the laboratory and used to induce an experimental infection of juvenile rainbow trout. The course of infection was followed by sampling for parasite enumeration, immunohistochemistry (IHC) and quantitative PCR (qPCR) on days 0, 5, 9 and 14 post-infection. IHC showed a significant increase in the occurrence of IgM-positive cells in the skin of the infected fish, whereas IgT-positive cells were eliminated and the number of CD8-positive cells declined. qPCR studies supported the IHC findings showing a significant increase in IgM and a decrease in the CD8 gene expression. In addition, genes encoding innate immune genes such as lysozyme, SAA and cathelicidin 2 were up-regulated. Expression of cytokines (IL-1β, IL-4/13A, IL-6, IL-8, IL-10), the cell marker CD4 and the transcription factor GATA3 showed a significant increase after infection. Cytokine profiling including up-regulation of IL-4/13A and IL-10 genes and transcription factor GATA3 connected to the proliferation of IgM producing lymphocytes suggests a partial shift towards a Th2 response associated with the I. necator infection.

Azumiobodo hoyamushi, the kinetoplastid causing soft tunic syndrome in ascidians, may invade through the siphon wall

The infectious kinetoplastid Azumiobodo hoyamushi causes 'soft tunic syndrome', a serious problem in aquaculture of the edible ascidian Halocynthia roretzi. Infection tests using diseased tunics demonstrated that juvenile (0.8 yr old) individuals never developed soft tunic syndrome, but all individuals in the other age groups (1.8, 2.8, and 3.8 yr old) showed the disease symptoms. In the infection tests, tunic softening was first observed at the tunic around siphons. Based on ultrastructural observation of the inner wall of the branchial siphon, the tunic lining the inner wall in juveniles (0.5 yr old) was completely covered with cuticle, which had a dense structure to prevent bacterial and protist invasion. In contrast, the tunic was often partly damaged and not covered with cuticle in healthy adults (≥2.5 yr old). The damaged tunic in the siphon wall could be an entrance for A. hoyamushi into the tunic of adult hosts.

Hypoxemia-induced leptin secretion: a mechanism for the control of food intake in diseased fish

Leptin is a potent anorexigen, but little is known about the physiological conditions under which this cytokine regulates food intake in fish. In this study, we characterized the relationships between food intake, O2-carrying capacity, liver leptin-A1 (lep-a1) gene expression, and plasma leptin-A1 in rainbow trout infected with a pathogenic hemoflagellate, Cryptobia salmositica. As lep gene expression is hypoxia-sensitive and Cryptobia-infected fish are anemic, we hypothesized that Cryptobia-induced anorexia is mediated by leptin. A 14-week time course experiment revealed that Cryptobia-infected fish experience a transient 75% reduction in food intake, a sharp initial drop in hematocrit and hemoglobin levels followed by a partial recovery, a transient 17-fold increase in lep-a1 gene expression, and a sustained increase in plasma leptin-A1 levels. In the hypothalamus, peak anorexia was associated with decreases in mRNA levels of neuropeptide Y (npy) and cocaine- and amphetamine-regulated transcript (cart), and increases in agouti-related protein (agrp) and pro-opiomelanocortin A2 (pomc). In contrast, in non-infected fish pair-fed to infected animals, lep-a1 gene expression and plasma levels did not differ from those of non-infected satiated fish. Pair-fed fish were also characterized by increases in hypothalamic npy and agrp, no changes in pomc-a2, and a reduction in cart mRNA expression. Finally, peak infection was characterized by a significant positive correlation between O2-carrying capacity and food intake. These findings show that hypoxemia, and not feed restriction, stimulates leptin-A1 secretion in Cryptobia-infected rainbow trout and suggest that leptin contributes to anorexia by inhibiting hypothalamic npy and stimulating pomc-a2.

In vitro and in vivo efficacy of drugs against the protozoan parasite Azumiobodo hoyamushi that causes soft tunic syndrome in the edible ascidian Halocynthia roretzi (Drasche)

It was discovered recently that infection by a protozoan parasite, Azumiobodo hoyamushi, is the most probable cause for soft tunic syndrome in an edible ascidian, Halocynthia roretzi (Drasche). In an attempt to develop measures to eradicate the causative parasite, various drugs were tested for efficacy in vitro and in vivo. Of the 20 antiprotozoal drugs having different action mechanisms, five were found potent (24-h EC50  < 10 mg L(-1) ) in their parasite-killing effects: formalin, H2 O2 , bithionol, ClO2 and bronopol. Moderately potent drugs (10 < 24-h EC50  < 100 mg L(-1) ) were quinine, fumagillin, amphotericin B, ketoconazole, povidone-iodine, chloramine-T and benzalkonium chloride. Seven compounds, metronidazole, albendazole, paromomycin, nalidixic acid, sulfamonomethoxine, KMnO4 , potassium monopersulphate and citric acid, exhibited EC50  > 100 mg L(-1) . When ascidians were artificially infected with A. hoyamushi, treated using 40 mg L(-1) formalin, bronopol, ClO2 , or H2 O2 for 1 h and then monitored for 24 h, very low mortality was observed. However, the number of surviving parasite cells in the ascidian tunic tissues was significantly reduced by treating with 40 mg L(-1) formalin or ClO2 for 1 h. The data suggest that we might be able to develop a disinfection measure using a treatment regimen involving commonly available drugs.

Detection of the kinetoplastid Azumiobodo hoyamushi, the causative agent of soft tunic syndrome, in wild ascidians Halocynthia roretzi

The occurrence of soft tunic syndrome in wild populations of the ascidian Halocynthia roretzi was monitored by diving at 5 to 6 sites in Miyagi Prefecture in Japan in summer 2010 and 2011. These sites were located at varying distances from farming sites at which the disease had previously been detected. All dead ascidians were collected, and their tunics were examined for Azumiobodo hoyamushi, the causative agent of soft tunic syndrome, using 18S rRNA PCR. In both years, <1% of wild ascidians we observed (18 out of 2100 in 2010, and 30 out of 3100 in 2011) were dead. The flagellates were only detected in 8 out of 18 dead ascidians from 3 sites in 2010, and 4 out of 30 from 2 sites in 2011. Healthy ascidians were successfully experimentally infected with the disease by immersing tunic samples from diseased wild ascidians into the rearing water. When apparently healthy ascidians collected from the wild population were reared for 40 d using pathogen-free water, the tunics of some ascidians became softened. The flagellates were detected in these individuals, which were diagnosed with soft tunic syndrome. Our results suggest that soft tunic syndrome affects the wild population of ascidians in Japan.

Duress without stress: Cryptobia infection results in HPI axis dysfunction in rainbow trout

Despite clear physiological duress, rainbow trout (Oncorhynchus mykiss) infected with the pathogenic haemoflagellate Cryptobia salmositica do not appear to mount a cortisol stress response. Therefore, we hypothesized that the infection suppresses the stress response by inhibiting the key effectors of the hypothalamic-pituitary-interrenal (HPI) axis. To test this, we characterized the basal activity of the HPI axis and the cortisol response to air exposure in saline- and parasite-injected fish. All fish were sampled at 4 and 6 weeks post-injection (wpi). While both the treatment groups had resting plasma cortisol levels, the parasite-infected fish had lower levels of plasma ACTH than the control fish. Relative to the control fish, the infected fish had higher mRNA levels of brain pre-optic area corticotrophin-releasing factor (CRF) and pituitary CRF receptor type 1, no change in pituitary POMC-A1, -A2 and -B gene expression, higher and lower head kidney melanocortin 2 receptor mRNA levels at 4 and 6 wpi respectively and reduced gene expression of key proteins regulating interrenal steroidogenesis: StAR, cytochrome P450scc and 11β-hydroxylase. The parasite-infected fish also had a reduced plasma cortisol response to a 60-s air exposure stressor. Superfusion of the head kidney tissues of the parasite-infected fish led to significantly lower ACTH-stimulated cortisol release rates than that observed in the control fish. These novel findings show that infection of rainbow trout with C. salmositica results in complex changes in the transcriptional activity of both central and peripheral regulators of the HPI axis and in a reduction in the interrenal capacity to synthesize cortisol.

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.

Cortisol and dexamethasone increase the in vitro multiplication of the haemoflagellate, Cryptobia salmositica, possibly by interaction with a glucocorticoid receptor-like protein

Cryptobia salmositica is a pathogenic haemoflagellate of Pacific salmon, Oncorhynchus spp., on the west coast of North America. The in vitro multiplication of the parasite was significantly enhanced by the addition of cortisol (within a range consistent with physiological levels in salmonid fishes; 10-50 ng ml(-1)) to the culture medium (MEM supplemented with FBS). However, higher cortisol concentrations (100 and 200 ng ml(-1)) either had no enhancing effects or resulted in lower replication rates compared with the controls. The synthetic glucocorticoid, dexamethasone (Dex), also stimulated the replication of the parasite and mifepristone (RU486), a synthetic steroid that has glucocorticoid receptor (GR) antagonist properties, inhibited the stimulatory actions of both cortisol and Dex, when added to the medium at a concentration of 100 ng ml(-1) co-culture with cortisol or Dex. Furthermore, the dose-dependent effects of glucocorticoids (cortisol and Dex) on the multiplication of the haemoflagellate were correlated with the initial size of the inocula. The study revealed a novel relationship between the parasite and its host, in which the host's cortisol is used by the parasite to enhance its replication. Also, since C. salmositica responds to both native and synthetic glucocorticoids and to the GR antagonist, RU486, and exhibits a biphasic (hormetic) response to the amount of cortisol in the medium, we propose that the glucocorticoid exerts its effects via an interaction with GR-like proteins in C. salmositica that are functionally similar to those present in vertebrate cells.

Chemosensory response of marine flagellate towards L- and D- dissolved free amino acids generated during heavy grazing on bacteria

This study investigated the generation of dissolved free amino acids (DFAA) by the bacterivorous flagellate Rhynchomonas nasuta when feeding on abundant prey. Specifically, it examined whether this flagellate protist exhibits a chemosensory response towards those amino acids. The concentrations of glycine and the L- and D-enantiomers of glutamate, serine, threonine, alanine, and leucine were determined in co-cultures of the flagellate and bacteria. Glycine, L- and D-alanine, and L-serine were found to accumulate under these conditions in amounts that correlated positively with flagellate abundance, suggesting that protists are involved in their generation. Investigations of the chemotactic response of young and old foraging protists to the same amino acids, offered in concentrations similar to those previously generated, showed that glycine elicited the strongest attraction in both age groups. Young protists were strongly attracted to all the assayed amino acids, whereas older protists maintained a high level of attraction only for glycine. These results suggest that glycine generated by protists actively grazing in bacterially enriched patches functions as an infochemical, signaling to foraging protists the presence of available prey in the aquatic environment.

[Spatial structure of communities of heterotrophic flagellates from a sphagnum bog]

Spatial distribution pattern of heterotrophic flagellates within a macroscopically homogenous sphagnum parcel of a transitional bog in the southern taiga was studied. Under investigation was horizontal pattern at different scales (1 cm, 10 cm, 1 m, 10 m) and the vertical heterogeneity of the community in the sphagnum quagmire. 105 species and forms of heterotrophic flagellates were revealed. Predominating were euglenids, less abundant are kynetoplastids and cercomonads. The most numerous appeared to be Cryptomonas sp., Heteromita minima, Goniomonas truncata, Protaspis simplex, Bodo designis, B. saltans, Phyllomitus apiculatus, Paraphysomonas sp., Petalomonas minuta. More abundant species were characterized by less patchy distribution than less abundant. At a smaller scale, the community was formed by the species with different degree of patchiness while at larger scales, all the species possess nearly the same distribution pattern. The same number of samples of equal sizes revealed nearly the same species numbers independently of distances between the sample sites, as the samples at each scale differ from each other nearly at the same magnitude. An averaged size of the species aggregations in the community is as large as several centimeters. Such a scale is probably a characteristic size (minimum area) of the community of the sphagnum dwelling heterotrophic flagellates. Rather low environmental heterogeneity within the sphagnum quagmire leads to significant homogeneity of the community at larger scales. Vertical differentiation of the heterotrophic flagellate community within that quagmire appeared to be very unstable with the time. The same species are characterized by different preferences to the depths at different spatial-temporal loci. Specific vertical distributions and community patterns are formed under different local conditions.

Susceptibility of sexually mature rainbow trout, Oncorhynchus mykiss to experimental cryptobiosis caused by Cryptobia salmositica

Sexually mature rainbow trout, Oncorhynchus mykiss, were highly susceptible to cryptobiosis caused by Cryptobia salmositica. Spawning female trout were more susceptible (higher parasitaemia and mortality) than sexually mature males. Most infected female trout (seven of nine) with eggs died before or shortly after spawning; however, none of the nine infected sexually matured males or the uninfected fish died. There was no significant difference in the severity of the anaemia between infected male and female trout. All infected males developed exophthalmia, while this clinical sign was not seen in any of the infected females nor in uninfected trout. The addition of 17 beta-estradiol (at physiological level or higher) did not enhance in vitro multiplication of the Cryptobia; however, fresh plasma from sexually mature females or males when added to cultures significantly increased in vitro multiplication of the pathogen. In addition, plasma from sexually mature females were significantly better than those from males in promoting in vitro parasite multiplication. Parasite multiplication did not increase after plasma from sexually mature fish were heat inactivated.

The role of quorum sensing mediated developmental traits in the resistance of Serratia marcescens biofilms against protozoan grazing

Resistance against protozoan grazers is a crucial factor that is important for the survival of many bacteria in their natural environment. However, the basis of resistance to protozoans and how resistance factors are regulated is poorly understood. In part, resistance may be due to biofilm formation, which is known to protect bacteria from environmental stress conditions. The ubiquitous organism Serratia marcescens uses quorum sensing (QS) control to regulate virulence factor expression and biofilm formation. We hypothesized that the QS system of S. marcescens also regulates mechanisms that protect biofilms against protozoan grazing. To investigate this hypothesis, we compared the interactions of wild-type and QS mutant strains of S. marcescens biofilms with two protozoans having different feeding types under batch and flow conditions. Under batch conditions, S. marcescens forms microcolony biofilms, and filamentous biofilms are formed under flow conditions. The microcolony-type biofilms were protected from grazing by the suspension feeder, flagellate Bodo saltans, but were not protected from the surface feeder, Acanthamoeba polyphaga. In contrast, the filamentous biofilm provided protection against A. polyphaga. The main findings presented in this study suggest that (i) the QS system is not involved in grazing resistance of S. marcescens microcolony-type biofilms; (ii) QS in S. marcescens regulates antiprotozoan factor(s) that do not interfere with the grazing efficiency of the protozoans; and (iii) QS-controlled, biofilm-specific differentiation of filaments and cell chains in biofilms of S. marcescens provides an efficient mechanism against protozoan grazing.

Rafts and sphingolipid biosynthesis in the kinetoplastid parasitic protozoa

Summary relatively large rafts are a feature of activated mammalian cells. These studies allow us to consider the functional role of lipid rafts in kinetoplastid parasites, which are particularly rich in lipid-anchored surface molecules. Morphological, biochemical and genetic studies indicate that lipid rafts (and sphingolipid biosythesis) are important in the differentiation of extracellular Leishmania to mammalian-infective metacyclic promastigotes, perhaps orchestrating the clearly observable reorganization of the plasma membrane during this process that leads to an activated metacyclic primed for invasion. However, the first step in the sphingolipid biosynthetic pathway (mediated by serine palmitoyltransferase), and at least regulated, de novo sphingoid base and ceramide synthesis, are not essential for the pathogenesis of intramacrophage Leishmania amastigotes.

Leishmania parasites (Kinetoplastida: Trypanosomatidae) reversibly inhibit visceral muscle contractions in hemimetabolous and holometabolous insects

Female sand flies can acquire protozoan parasites in the genus Leishmania when feeding on an infected vertebrate host. The parasites complete a complex growth cycle in the sand fly gut until they are transmitted by bite to another host. Recently, a myoinhibitory peptide was isolated from Leishmania major promastigotes. This peptide caused significant gut distension and reversible, dose-dependent inhibition of spontaneous hindgut contractions in the enzootic sand fly vector, Phlebotomus papatasi. The current study further characterizes myoinhibitory activity in L. major and other kinetoplastid parasites, using the P. papatasi hindgut and other insect organ preparations. Myoinhibitory activity was greatest in cultured promastigotes and in culture medium in late log-phase and early stationary-phase, coinciding with development of infective Leishmania morphotypes in the sand fly midgut. L. major promastigote lysates inhibited spontaneous contractions of visceral muscle preparations from hemimetabolous (Blattaria and Hemiptera) and holometabolous (Diptera) insects. Inhibition of visceral muscle contractions in three insect orders indicates a conserved mode of action. Myoinhibitory activity was detected also in Leishmania braziliensis braziliensis, a Sudanese strain of Leishmania donovani, and the kinetoplastid parasite Leptomonas seymouri. Protozoan-induced myoinhibition mimics the effect of insect myotropins. Inhibiting host gut contractions protects Leishmania parasites from being excreted after blood meal and peritrophic matrix digestion, allowing development and transmission of infective forms.

Mitochondrial differentiation in kinetoplastid protozoa: a plethora of RNA controls

Differentiation of kinetoplastid protozoa during their complex life cycles is accompanied by stepwise changes in mitochondrial functions. Recent studies have begun to reveal multilevel post-transcriptional regulatory mechanisms by which the expression of the nuclear and mitochondrially encoded components of respiratory enzymes is coordinated, as well as the identities of some general and gene-specific factors controlling mitochondrial differentiation.

Behavioural interactions, kin and disease susceptibility in the bumblebee Bombus terrestris

Behavioural interactions are often analysed in terms of their costs and benefits to the actors [Hamilton, (1964) J. Theor. Biol.7 1-16; Gadagkar, (1993) Trends Ecol. Evol.8 232-234; Foster et al., (2001) Ann. Zool. Fenn.38 229-238]. Using the bumblebee Bombus terrestris, we wish to distinguish between two possible determinants of interaction behaviour between conspecifics, namely kin-directed behaviour that reflects genetic distance between individuals, or, alternatively, interactions guided by a functional distance between individuals, specifically, with respect to disease susceptibility. We find no relationship between contact rate of individuals and the genetic distance of their respective colonies. Interestingly, we do find a significant negative correlation between contact rate and the distance between the two colonies in susceptibility to a spectrum of parasite strains. This cannot be explained by either of the a priori alternatives so we propose two further testable hypotheses to explain our results.

Microcolonies, quorum sensing and cytotoxicity determine the survival of Pseudomonas aeruginosa biofilms exposed to protozoan grazing

This study was based on the hypothesis that biofilms of the opportunistic pathogen Pseudomonas aeruginosa are successfully adapted to situations of protozoan grazing. We tested P. aeruginosa wild type and strains that were genetically altered, in structural and regulatory features of biofilm development, in response to the common surface-feeding flagellate Rhynchomonas nasuta. Early biofilms of the wild type showed the formation of grazing resistant microcolonies in the presence of the flagellate, whereas biofilms without the predator were undifferentiated. Grazing on biofilms of quorum sensing mutants (lasR and rhlR/lasR) also resulted in the formation of microcolonies, however, in lower numbers and size compared to the wild type. Considerably fewer microcolonies than the wild type were formed by mutant cells lacking type IV pili, whereas no microcolonies were formed by flagella-deficient cells. The alginate-overproducing strain PDO300 developed larger microcolonies in response to grazing. These observations suggest a role of quorum sensing in early biofilms and involvement of flagella, type IV pili, and alginate in microcolony formation in the presence of grazing. More mature biofilms of the wild type exhibited acute toxicity to the flagellate R. nasuta. Rapid growth of the flagellate on rhlR/lasR mutant biofilms indicated a key role of quorum sensing in the upregulation of lethal factors and in grazing protection of late biofilms. Both the formation of microcolonies and the production of toxins are effective mechanisms that may allow P. aeruginosa biofilms to resist protozoan grazing and to persist in the environment.

Effect of Cryptobia salmositica-induced anorexia on feeding behavior and immune response in juvenile rainbow trout Oncorhynchus mykiss

At 10 degrees C, rainbow trout Oncorhynchus mykiss (n = 13 per group) infected with Cryptobia salmositica Katz, 1951 became anorexic at 3 wk post-infection (w.p.i.), with feed-intake decreasing significantly from 1.33 to 0.94% body weight (b.w.). Anorexia was most severe at 4 w.p.i. (0.80% b.w.), coinciding with peak parasitemia (9.2 x 10(6) parasites ml blood(-1)) and anemia. At 8 w.p.i., fish had recovered their appetite although they still had contained detectable parasites (6.8 x 10(5) parasites ml(-1)) and were anemic (pack cell volume, PCV, of 24.4%). However at 5 degrees C, anorexia occurred at 5 w.p.i. (0.81% b.w.), and was most severe at 7 w.p.i. (0.40% b.w.). At 8 w.p.i. (0.43% b.w.), fish displayed high parasitemia (4.6 x 10(6) parasites ml(-1)) and low PCV (10.8%). Fish at 5 degrees C had lower gastric evacuation (GE) rates (GE48h) than 10 degrees C fish, however there were no differences between infected and naive fish at both temperatures. Before anorexia, there was no significant correlation between mean share of meal (MSM, a measure of how food was partitioned within a group) and coefficient of variation in feeding but this became significant during anorexia (p = 0.02 and p = 0.0002 at 10 and 5 degrees C respectively). Significant correlations were detected between b.w. and MSM before onset of anorexia at 10 degrees C (p = 0.005) and 5 degrees C (p = 0.02); this was maintained at 10 degrees C (p = 0.001) but not at 5 degrees C (p = 0.98). Fish on an anorexic diet (0.93% b.w.) responded well at 10 degrees C to a live C. salmositica vaccine; this could partly be due to constant antigenic stimulation by the live vaccine.

Cryptobia (Trypanoplasma) salmositica and salmonid cryptobiosis

Salmonid cryptobiosis is caused by Cryptobia (Trypanoplasma) salmositica. The haemoflagellate has been reported from all species of Pacific Oncorhynchus spp. on the west coast of North America. It is normally transmitted by the freshwater leech, Piscicola salmositica, in streams and rivers, and sculpins, Cottus spp., are considered important reservoir hosts. The pathogen can also survive on the body surface of fish because it has a contractile vacuole to osmoregulate when the fish is in fresh water. This allows for direct transmission between fish, especially in aquaculture facilities. The parasite divides rapidly by binary fission in the blood to cause disease, the severity of which is directly related to parasitaemia. Cryptobia salmositica has a mitochondrium and it normally undergoes aerobic respiration; however, if its mitochondrium is damaged it will switch to glycolysis. Its glycolytic enzymes and catalase are contained in glycosomes. Cysteine protease is a metabolic enzyme, and its neutralization inhibits oxygen consumption and multiplication of the parasite. An important virulent factor in cryptobiosis is a secretory metalloprotease. The protective mechanism involves production of complement fixing antibodies, phagocytosis by macrophages, and cell-mediated cytotoxicity. Recovered fish are protected, probably for life as the immunity is non-sterile. Clinical signs of the disease include anaemia, anorexia, splenomegaly, general oedema and abdominal distension with ascites. The metabolism and swimming performance of infected fish are significantly reduced and the bioenergetic cost of the disease is very considerable. Fish are susceptible to hypoxia and their immune system is depressed during acute cryptobiosis. Severity of the disease and mortality rates vary significantly between species and stocks of salmon. Protective strategies include selective breeding of Cryptobia-resistant fish. This is innate resistance to infection and it is controlled by a dominant Mendelian locus. In these fish the parasite is lysed via the alternative pathway of complement activation. In Cryptobia-tolerant fish (infected with the pathogen but which do not suffer from disease) the metalloprotease secreted by the parasite is neutralized by alpha2 macroglobulin. Hence, the production of a transgenic Cryptobia-tolerant salmon is an option. This strategy has the advantage in that human intervention (e.g. vaccination, chemotherapy) is not required once the transgenic fish is produced. Acquired immunity is another option; a single dose of the attenuated live vaccine protects fish for at least 2 years. The protective mechanism in vaccinated fish is similar to that in recovered fish. The trypanocidal drug, isometamidium chloride, is an effective therapeutic and prophylactic agent. It accumulates in the mitochondrium of the parasite and significantly disrupts aerobic respiration by causing lesions in the organelle. Efficacy of the drug is significantly increased after its conjugation to antibodies. This immuno-chemotherapeutic strategy has the advantage in that it will lower the drug dosage and hence side-effects of chemotherapy. It will probably reduce the accumulation of the drug in fish, an important consideration in food fish.

The endocytic apparatus of the kinetoplastida. Part II: machinery and components of the system

Endocytic systems within eukaryotic cells are a diverse set of intracellular transport pathways responsible for uptake, recycling, interaction with the exocytic system and degradation of molecules. Each of these pathways requires the interaction of distinct protein components that function in macromolecule sorting, control of transport rates and in membrane biogenesis. In the second of two articles on kinetoplastida endocytosis, the endocytic system in Trypanosoma brucei is considered as a model, and the molecules that control this system and the protein components of the endocytic pathway are discussed. We also consider novel mechanisms for sorting that have been proposed to operate in trypanosomes.

Carboxy terminal domain of the largest subunit of RNA polymerase II of Leishmania donovani has an unusually low number of phosphorylation sites

BACKGROUND

The C-terminal domain (CTD) of the largest subunit of RNA polymerase II in higher eukaryotes has an altered form in Leishmania donovani. To determine whether this is a general feature of the kinetoplastida and to investigate the role of this domain in parasitic RNA pol II transcription, we isolated the gene encoding RNA pol II LS (rpolIILS) and analyzed its C-terminal domain. The discreteness observed may be due to a functional constraint delineating parasite from host.

MATERIAL/METHODS

The gene for L. donovani rpolIILS was picked up and sequenced. The CTD of L. donovani rpolIILS was purified as a His-tagged recombinant protein and phosphorylated with a crude kinase extract from L. donovani. An immunoblot analysis of the phosphorylated CTD and photo-crosslinked L. donovani nuclear extracts was done using anti-CTD antibody.

RESULTS

The L. donovani rpolIILS is encoded by a single-copy gene. Its transcript is matured postranscriptionally, with the mini-exon trans-spliced 397 bases upstream of the initiation site. The uniqueness of Leishmania rpolIILS CTD according to prediction analysis was corroborated with in vitro phosphorylation of the recombinant protein. Photoaffinity labelling of L. donovani nuclear run-on transcripts and immunoblot analysis using anti-CTD antibody could identify the active form of RNA polymerase II enzyme in this parasite.

CONCLUSIONS

The L. donovani rpolIILS possesses a unique C-terminal extension lacking the characteristic repeats but containing serine residues as a potential phosphorylation site. Anti-CTD antibody could recognize a single molecular species for the RNA pol II enzyme in L. donovani.

Endocytosis in different lifestyles of protozoan parasitism: role in nutrient uptake with special reference to Toxoplasma gondii

A fundamental property of any eukaryotic cell is endocytosis, that is the ability to take up external fluid, solutes and particulate matter into membrane-bound intracellular vesicles by various mechanisms. Toxoplasma gondii is an intracellular protozoan parasite of the phylum Apicomplexa with a wide geographical and host range distribution. Significant progress in studying the cell biology of this parasite has been accomplished over the last few years. Only recently endocytic compartments and endocytic trafficking have come to a closer dissection in T. gondii. In this review, we discuss the evidence for an endocytic compartment and present a model for an endocytic pathway in Toxoplasma against a background of endocytosis in kinetoplastida and the extensive insights gained from mammalian and yeast cells.

A novel trypanoplasm-like flagellate Jarrellia atramenti n. g., n. sp. (Kinetoplastida: Bodonidae) and ciliates from the blowhole of a stranded pygmy sperm whale Kogia breviceps (Physeteridae): morphology, life cycle and potential pathogenicity

The successful 6 mo rehabilitation of a stranded juvenile pygmy sperm whale Kogia breviceps afforded the opportunity to study the poorly known protozoan fauna of the upper respiratory tract of cetaceans. Mucus samples were collected by holding either a petri dish or glass slides over the blowhole for 3 to 5 exhalations; preparations were examined as wet mounts, and then stained with Wrights-Giemsa or Gram stain. Blood smears were stained with Wrights-Giemsa. Unidentified spindle-shaped and unidentified broad ciliates, reported from the blowhole of the pygmy sperm whale for the first time, were seen only initially, while yeast-like organisms and bacteria were seen intermittently. Epithelial cells and white blood cells were often present in the blowhole mucus, but red blood cells were never seen. A novel trypanoplasm-like bodonid kinetoplastid biflagellate (Order Kinetoplastida) was commonly encountered in the blowhole mucus, but never in the blood. Both mature flagellates and those undergoing longitudinal binary fission were present. The elongate flagellate had a long whiplash anterior flagellum; the recurrent flagellum was attached along at least two-thirds of the body length, forming a prominent undulating membrane, and the trailing portion was short. The kinetoplast was irregularly fragmented. The flagellates were either free-swimming, or attached to host material via the free portion of the posterior flagellum. The prominent undulating membrane was characteristic of Trypanoplasma, while the fragmented kinetoplast was characteristic of some species of Cryptobia. For the novel bodonid kinetoplastid, with its unique combination of morphological features (prominent undulating membrane and fragmented kinetoplast), we propose the creation of a new genus Jarrellia. We believe this to be the first published description of a flagellate from a marine mammal, and among the first reports of a trypanoplasm-like flagellate from a warm-blooded host. We expect that a diversity of flagellates and ciliates are commonly present in the blowhole of cetaceans. Future studies on the identity of the protozoans and the health of their cetacean hosts, which are readily studied in captivity, are necessary to establish their status as commensals or parasites.

Early evolutionary origin of the planktic foraminifera inferred from small subunit rDNA sequence comparisons

Phylogenetic analysis of five partial planktic foraminiferal small subunit (SSU) ribosomal (r) DNA sequences with representatives of a diverse range of eukaryote, archaebacterial, and eubacterial taxa has revealed that the evolutionary origin of the foraminiferal lineage precedes the rapid eukaryote diversification represented by the "crown" of the eukaryotic tree and probably represents one of the earliest splits among extant free-living aerobic eukaryotes. The foraminiferal rDNA sequences could be clearly separated from known symbionts, commensals, and food organisms. All five species formed a single monophyletic group distinguished from the "crown" group by unique foraminiferal specific insertions as well as considerable nucleotide distance in aligned regions.

Phylogenetic position of kinetoplastid protozoa inferred from the protein phylogenies of elongation factors 1alpha and 2

Partial regions of the mRNA encoding a major part of translation elongation factor 2 (EF-2) from a kinetoplastid protozoan, Trypanosoma cruzi, were amplified by means of polymerase chain reaction and their primary structures were analyzed. The deduced amino acid sequence was aligned with those of other eukaryotic and archaebacterial EF-2s, and the phylogenetic relationships among eukaryotes were inferred by the maximum likelihood (ML) method. ML analyses of EF-2 phylogeny using six different stochastic models of amino acid substitutions consistently suggested that the phylogenetic position of T. cruzi is likely to be closer to higher eukaryotes than that inferred from the phylogeny of small subunit ribosomal RNA (SrRNA). These results are consistent with those for the elongation factor 1alpha (EF-1alpha) phylogeny. When the EF-1alpha and EF-2 phylogenies were totally evaluated, it became much clearer that the divergence of T. cruzi occurred later than that of a mitochondrion-lacking protozoan, Entamoeba histolytica, although this is not conclusive.

Protein trafficking in kinetoplastid protozoa

The kinetoplastid protozoa infect hosts ranging from invertebrates to plants and mammals, causing diseases of medical and economic importance. They are the earliest-branching organisms in eucaryotic evolution to have either mitochondria or peroxisome-like microbodies. Investigation of their protein trafficking enables us to identify characteristics that have been conserved throughout eucaryotic evolution and also reveals how far variations, or alternative mechanisms, are possible. Protein trafficking in kinetoplastids is in many respects similar to that in higher eucaryotes, including mammals and yeasts. Differences in signal sequence specificities exist, however, for all subcellular locations so far examined in detail--microbodies, mitochondria, and endoplasmic reticulum--with signals being more degenerate, or shorter, than those of their higher eucaryotic counterparts. Some components of the normal array of trafficking mechanisms may be missing in most (if not all) kinetoplastids: examples are clathrin-coated vesicles, recycling receptors, and mannose 6-phosphate-mediated lysosomal targeting. Other aspects and structures are unique to the kinetoplastids or are as yet unexplained. Some of these peculiarities may eventually prove to be weak points that can be used as targets for chemotherapy; others may turn out to be much more widespread than currently suspected.

Metabolism and functions of trypanothione in the Kinetoplastida

Trypanosomatids differ from all other organisms in their ability to conjugate the sulfur-containing tripeptide, glutathione, and the polyamine, spermidine, to form trypanothione [N1,N8-bis(glutathionyl)spermidine]. Together with the NADPH-dependent flavoprotein, trypanothione reductase, the dithiol form of trypanothione provides an intracellular reducing environment in these parasites, substituting for glutathione and glutathione reductase found in the mammalian host. Trypanothione and its related enzymes are involved in defense against damage by oxidants, certain heavy metals, and possibly xenobiotics. Trypanothione and its metabolic precursor, glutathionylspermidine, are also implicated in the modulation of spermidine levels during growth. Several existing trypanocidal drugs interact with the trypanothione system, suggesting that trypanothione metabolism may be a good target for the development of new drugs. The purification and properties of three key enzymes (glutathionylspermidine synthetase, trypanothione synthetase, and trypanothione reductase) are discussed, and the catalytic mechanism, substrate-specificity, and the three-dimensional structure of trypanothione reductase are compared to that of glutathione reductase.

In vitro oxygen consumption and motility of Cryptobia salmositica, Cryptobia bullocki, and Cryptobia catostomi (Sarcomastigophora: Kinetoplastida)

Cryptobia salmositica (pathogenic and vaccine strains), Cryptobia bullocki (pathogenic), and Cryptobia catostomi (nonpathogenic) have similar oxygen consumption rates (0.17 +/- 0.01 nm O2/10(6) parasites). Incubation with sodium azide (5 microliters of a 1-M solution to 1 ml of parasite suspension, i.e., a 5-mM final concentration) reduced the oxygen consumption by approximately 4.5-fold. Motility of the parasites was also greatly reduced in sodium azide. The oxygen consumption and motility of the parasites returned to preazide treatment levels when the azide was removed even after 24 hr of incubation in sodium azide. The activities of hexokinase, pyruvate kinase, and cytochrome C oxidase were not detected in the 3 species of Cryptobia.