Parasitic Dinoflagellate Research Articles

A new host for Hematodinium infection among lithodid crabs from the Sea of Okhotsk.

A disease caused by parasitic dinoflagellates of the genus Hematodinium has been found in the soft crab Hapalogaster grebnitzkii from the Sea of Okhotsk, which is considered a new host for this agent among lithodid crabs. This report provides macro- and micromorphological descriptions (using light and transmission electron microscopy) of the disease, as well as molecular identification of Hematodinium sp. from soft crabs, based on 18S RNA sequence data.

The influence of temperature and salinity on mortality of recently recruited blue crabs, Callinectes sapidus, naturally infected with Hematodinium perezi (Dinoflagellata).

The parasitic dinoflagellate Hematodinium perezi is highly prevalent in juvenile blue crabs, Callinectes sapidus, along the eastern seaboard of the USA. Although the parasite is known to kill adult crabs, the mortality rate of naturally infected juvenile crabs remains unknown. We analyzed the influence of temperature and salinity on the mortality of recently recruited blue crabs that were naturally infected with H. perezi. Over 492 juvenile crabs (infected, n = 282; uninfected controls, n = 210) were held individually in six-well plates and held at six temperatures (4, 10, 15, 20, 25, and 30 °C) or three salinities (5, 15, and 30 psu) for a maximum of 90 days. Mortality of infected crabs was 10 times higher at elevated temperatures (25 and 30 °C) and salinity (30 psu) compared to uninfected control treatments. By contrast, infected crabs exposed to mild temperatures (10, 15, and 20 °C) showed a high survival (>80%), no different than uninfected control treatments. Infected crabs at the lowest temperature (4 °C) exhibited a high mortality, but the intensity of infection was lower than in the other temperature treatments. In addition, this study revealed the optimal temperature (25 °C) and salinity (30 psu) for H. perezi to progress in its life cycle leading to sporulation in juvenile crabs; 31.6% (19/60) of crabs held under these conditions released dinospores of H. perezi after 10 days. Crabs held at other temperatures did not release dinospores over the time course of the experiment. Infected crabs were capable of molting and in most cases molted at the same frequency as uninfected crabs serving as controls. The mortality observed in this study indicates that early benthic juveniles will experience significant mortality due to H. perezi with increasing ocean temperatures and that this mortality may be a significant factor in the recruitment of blue crabs to high salinity regions.

Protistan parasites along oxygen gradients in a seasonally anoxic fjord: A network approach to assessing potential host-parasite interactions

The seasonally stratified water column of Saanich Inlet, Vancouver, B.C., Canada provides a natural laboratory for examining how ocean deoxygenation shapes microbial community population dynamics and interactions. Microbial eukaryotes within these communities play significant roles as phototrophs, mixotrophs, symbionts, predators, parasites, and saprotrophs, with population abundances and interactions changing seasonally, and along water column redox gradients. Here, we use time series observations of ribosomal RNA and DNA diversity in combination with co-occurrence correlation and indicator species analyses to observe microbial eukaryote community dynamics over a 12-month period, uncovering significant correlations between parasitic dinoflagellates within Syndiniales and other eukaryotic taxa during months of peak water column stratification. Syndiniales operational taxonomic units (OTUs) were the most abundant indicator OTUs during stratification. Syndiniales OTUs exhibited significant correlations with a broad range of taxa, including members of Apicomplexa, Ciliophora, Dinoflagellata, Chlorophyta, Metazoa and a variety of Stramenopiles including MAST groups. Correlation analyses suggest Syndiniales may influence phytoplankton bloom dynamics in Saanich Inlet as well as abundances of protist and metazoan grazers that are indicator species for peak stratification periods. These observations shed light on the potential role of parasitic protists on organic matter release and bloom termination events during stratification and renewal periods in Saanich Inlet with potential implications for coastal marine foodwebs and fisheries productivity.

Differential host mortality explains the effect of high temperature on the prevalence of a marine pathogen.

Infectious diseases threaten marine populations, and the extent of their impacts is often assessed by prevalence of infection (the proportion of infected individuals). Changes in prevalence are often attributed to altered rates of transmission, although the rates of birth, recovery, and mortality also determine prevalence. The parasitic dinoflagellate Hematodinium perezi causes a severe, often fatal disease in blue crabs. It has been speculated that decreases in prevalence associated with high temperatures result from lower rates of infection. We used field collections, environmental sensor data, and high-temperature exposure experiments to investigate the factors that change prevalence of infections in blue crab megalopae (post-larvae). These megalopae migrate from offshore waters, where temperatures are moderate, to marshes where temperatures may be extremely high. Within a few days of arriving in the marsh, the megalopae metamorphose into juvenile crabs. We found a strong negative association between prevalence of Hematodinium infection in megalopae and the cumulative time water temperatures in the marsh exceeded 34°C over the preceding two days. Temperatures this high are known to be lethal for blue crabs, suggesting that higher mortality of infected megalopae could be the cause of reduced prevalence. Experimental exposure of megalopae from the marsh to a temperature of 34°C resulted in higher mortality for infected than uninfected individuals, and decreased the prevalence of infection among survivors from 18% to 3%.

Identification of unique microbiomes associated with harmful algal blooms caused by Alexandrium fundyense and Dinophysis acuminata

Biotic interactions dominate plankton communities, yet the microbial consortia associated with harmful algal blooms (HABs) have not been well-described. Here, high-throughput amplicon sequencing of ribosomal genes was used to quantify the dynamics of bacterial (16S) and phytoplankton assemblages (18S) associated with blooms and cultures of two harmful algae, Alexandrium fundyense and Dinophysis acuminata. Experiments were performed to assess changes in natural bacterial and phytoplankton communities in response to the filtrate from cultures of these two harmful algae. Analysis of prokaryotic sequences from ecosystems, experiments, and cultures revealed statistically unique bacterial associations with each HAB. The dinoflagellate, Alexandrium, was strongly associated with multiple genera of Flavobacteria including Owenweeksia spp., Maribacter spp., and individuals within the NS5 marine group. While Flavobacteria also dominated Dinophysis-associated communities, the relative abundance of Alteromonadales bacteria strongly co-varied with Dinophysis abundances during blooms and Ulvibacter spp. (Flavobacteriales) and Arenicella spp. (Gammaproteobacteria) were associated with cells in culture. Eukaryotic sequencing facilitated the discovery of the endosymbiotic, parasitic dinoflagellate, Amoebophrya spp., that had not been regionally described but represented up to 17% of sequences during Alexandrium blooms. The presence of Alexandrium in field samples and in experiments significantly altered the relative abundances of bacterial and phytoplankton by both suppressing and promoting different taxa, while this effect was weaker in Dinophysis. Experiments specifically revealed a negative feedback loop during blooms whereby Alexandrium filtrate promoted the abundance of the parasite, Amoebophrya spp. Collectively, this study demonstrates that HABs formed by Alexandrium and Dinophysis harbor unique prokaryotic and eukaryotic microbiomes that are likely to, in turn, influence the dynamics of these HABs.

Patterns in the natural transmission of the parasitic dinoflagellate Hematodinium perezi in American blue crabs, Callinectes sapidus from a highly endemic area

The dinoflagellate Hematodinium perezi is a highly pathogenic endoparasite that infects blue crabs Callinectes sapidus and other decapods. Annual outbreaks of the parasite along the eastern seaboard of the USA indicate that transmission occurs at high rates; however, the timing and incidence of new infections are unknown. The aim of this study was to investigate the patterns and factors associated with the natural transmission of Hematodinium in juvenile crabs from a highly endemic site. A novel field experiment, using naive crabs as sentinels, was implemented to measure transmission. Over 965 juvenile crabs (instars C3–C10) collected from a non-endemic site were deployed for set periods of 3, 7, 10, and 14 days at a highly endemic site. Prevalence was 5.1% after a 3-day deployment and 88% after a 10-day deployment. This corresponded to a daily incidence of new infections of 1.7 and 8.8%, in the population, respectively. New infections progressed very quickly; 50% of infected crabs developed heavy infections after only 14 days. The influence of host molting on the transmission of the parasite was investigated by tagging 467 crabs using cyanoacrylate glue and small plastic tags. After 7-, 10-, and 14-day deployments, sentinel crabs were assessed and infections were found not to be associated with host molting. Lastly, two storm events, with high rainfall, strong winds, and lower temperatures, disrupted the natural transmission of H. perezi to sentinel crabs, essentially halting transmission in the coastal system. These sentinel studies indicate that transmission can occur rapidly and at very high levels in endemic sites and that it can be quickly modulated by changes in environmental conditions following storm events. Infections by Hematodinium may increase host mortality and thus may be a threat to blue crab populations in endemic areas.

Disease ecology of Hematodinium perezi in a high salinity estuary: investigating seasonal trends in environmental detection.

The blue crab Callinectes sapidus has seen a general decline in population levels. One factor influencing mortality is infections by Hematodinium perezi, a dinoflagellate parasite. A 2 yr study was conducted in 2014 and 2015 to monitor H. perezi DNA within the Maryland (USA) coastal bays, comparing seasonal cycles in the abundance of parasite DNA in environmental samples to parasite presence in host blue crabs. A late summer to early fall peak in H. perezi infections in blue crabs was observed, consistent with previous work. Infection intensities matched this trend, showing a slow progression of low intensity infections early in the year, with a peak in moderate and heavy infections occurring between July and September, for both years. It was hypothesized that the peak in water column occurrence would coincide with those months when infection intensities were highest in blue crabs. As the peaks in water column occurrence were in July 2014 and August-September 2015, this is consistent with sporulation being the primary contributor to environmental detection in summer months. An additional peak in environmental detection occurred in both years during the early spring months, the cause of which is currently unknown but may be related to infections in overwintering crabs or alternate hosts. Several new crustacean hosts were identified within this estuary, including grass shrimp Palaemonetes spp. and the sand shrimp Crangon septemspinosa, as well as the mud crab Dyspanopeus sayi. Improved knowledge of this disease system will allow for better management of this important fishery.

Hematodinium spp. infections in wild and cultured populations of marine crustaceans along the coast of China.

The parasitic dinoflagellate Hematodinium spp. infects a broad range of marine crustaceans. Its epidemics have impacted wild populations of various commercial fishery species around the world and the sustainability of mariculture in China. To study the epidemiology of Hematodinium spp. in marine crustaceans along the coast of China, we conducted a broad survey of wild and cultured stocks of major crustacean species in 2013 to 2015. Hematodinium sp. infections were identified in wild stocks of Portunus trituberculatus from Huludao, Laizhou, Qingdao, Yangtze River Estuary and Zhoushan, and Scylla paramamosain from Shantou; and cultured stocks of Portunus trituberculatus and Penaeus monodon from a polyculture pond in Qingdao. In the polyculture pond, Hematodinium sp. infections were observed in Portunus trituberculatus from June until October, with peak prevalence (up to 90%) observed in late July to early August. Furthermore, Hematodinium sp. infection was identified for the first time in the giant tiger prawn Penaeus monodon in the polyculture system during the disease outbreak. Phylogenetic analysis indicated that the Hematodinium isolate infecting Penaeus monodon was identical to the isolate infecting the co-cultured Portunus trituberculatus, and it was grouped into H. perezi genotype II together with the other isolates reported in China. The Hematodinium sp. isolated from Portunus trituberculatus appeared to have similar life stages as the H. perezi genotype III isolated from the American blue crab Callinectes sapidus. Our study indicates that outbreaks of Hematodinium disease can be a significant threat to the widely used polyculture system for decapods in China that may be particularly vulnerable to such generalist pathogens.

Physiological responses of reared sea bream (Sparus aurata Linnaeus, 1758) to an Amyloodinium ocellatum outbreak.

Amyloodiniosis represents a major bottleneck for semi-intensive aquaculture production in Southern Europe, causing extremely high mortalities. Amyloodinium ocellatum is a parasitic dinoflagellate that can infest almost all fish, crustacean and bivalves that live within its ecological range. Fish mortalities are usually attributed to anoxia, associated with serious gill hyperplasia, inflammation, haemorrhage and necrosis in heavy infestations; or with osmoregulatory impairment and secondary microbial infections due to severe epithelial damage in mild infestation. However, physiological information about the host responses to A.ocellatum infestation is scarce. In this work, we analysed the proteome of gilthead sea bream (Sparus aurata) plasma and relate it with haematological and immunological indicators, in order to enlighten the different physiological responses when exposed to an A.ocellatum outbreak. Using 2D-DIGE, immunological and haematological analysis and in response to the A.ocellatum contamination we have identified several proteins associated with acute-phase response, inflammation, lipid transport, homoeostasis, and osmoregulation, wound healing, neoplasia and iron transport. Overall, this preliminary study revealed that amyloodiniosis affects some fish functional pathways as revealed by the changes in the plasma proteome of S.aurata, and that the innate immunological system is not activated in the presence of the parasite.

The diversity and structure of marine protists in the coastal waters of China revealed by morphological observation and 454 pyrosequencing

Pyrosequencing of the 18S rRNA gene has been widely adopted to study the eukaryotic diversity in various types of environments, and has an advantage over traditional morphology methods in exploring unknown microbial communities. To comprehensively assess the diversity and community composition of marine protists in the coastal waters of China, we applied both morphological observations and high-throughput sequencing of the V2 and V3 regions of 18S rDNA simultaneously to analyze samples collected from the surface layer of the Yellow and East China Seas. Dinoflagellates, diatoms and ciliates were the three dominant protistan groups as revealed by the two methods. Diatoms were the first dominant protistan group in the microscopic observations, with Skeletonema mainly distributed in the nearshore eutrophic waters and Chaetoceros in higher temperature and higher pH waters. The mixotrophic dinoflagellates, Gymnodinium and Gyrodinium, were more competitive in the oligotrophic waters. The pyrosequencing method revealed an extensive diversity of dinoflagellates. Chaetoceros was the only dominant diatom group in the pyrosequencing dataset. Gyrodinium represented the most abundant reads and dominated the offshore oligotrophic protistan community as they were in the microscopic observations. The dominance of parasitic dinoflagellates in the pyrosequencing dataset, which were overlooked in the morphological observations, indicates more attention should be paid to explore the potential role of this group. Both methods provide coherent clustering of samples. Nutrient levels, salinity and pH were the main factors influencing the distribution of protists. This study demonstrates that different primer pairs used in the pyrosequencing will indicate different protistan community structures. A suitable marker may reveal more comprehensive composition of protists and provide valuable information on environmental drivers.

A novel hematoxylin and eosin stain assay for detection of the parasitic dinoflagellate Amoebophrya

The parasitic dinoflagellate Amoebophrya infects broad range of marine organisms. Particularly, Amoebophrya infections in planktonic dinoflagellates can prevent or delay the formation of algal blooms, and recycle undergrazed planktonic dinoflagellates back to the microbial loop by disrupting host cells. Its ecological significance was gradually recognized along with the discovery of its enormous molecular diversity in oceanic and coastal ecosystems. Thus, we developed a reliable, easily accessible and less time-consuming assay, to detect and assess Amoebophrya infections in planktonic dinoflagellates. The modified hematoxylin and eosin staining assay provided reliable diagnosis of Amoebophrya infection by identifying the characteristic “beehive” of the multinucleate trophonts. After staining, the typical multinucleate “beehive” is evidently distinguishable from the compact nuclei of uninfected host cells. The modified hematoxylin and eosin (H & E) staining assay is easy to use, that can be routinely performed within 3h (up to 20 samples/batch) using general laboratory equipment, supplies and chemical reagents. The produced slides with agar-embedded dinoflagellate cells can be stored for several months or even years in a dry place without noticeable loss in quality of staining. With suitable calculation, the modified H & E assay can be applied to assess the prevalence of Amoebophrya infection in planktonic dinoflagellates. This efficient and powerful assay will facilitate the investigation on the ecological roles of Amoebophryidae in coastal and oceanic ecosystem.

Stress effects of amyloodiniosis in gilthead sea bream Sparus aurata.

Amyloodiniosis is a parasitological disease caused by one of the most common and important parasitic dinoflagellates in fish, Amyloodinium ocellatum (Brown), that represents a major bottleneck for gilthead seabream semi-intensive aquaculture in Southern Europe. In this experiment, we analyzed some metabolic, osmoregulatory and stress indicators to elucidate some of the physiological responses of gilthead sea bream when exposed to an A. ocellatum outbreak. We observed significant differences between Control and Infection groups in the cortisol, lactate and gill Na+/K+-ATPase (NKA) activity levels but that glucose, osmolarity, pH and total protein did not present such differences. This could indicate that the presence of the parasite induced a stress response, possibly enhancing the metabolization of glucose and subsequently lactate to cope with the higher energy requirements of the organism. There was also a decrease in gill NKA activity possibly due to severe epithelial damage and increased mucus production caused by the parasite A. ocellatum, which could induce anoxia and osmoregulatory impairment in the organism. However, further works must be performed to fully understand the physiological reactions of fish for A. ocellatum outbreaks.

Fiddler crabs (Uca spp.) as model hosts for laboratory infections of Hematodinium perezi

The parasitic dinoflagellate, Hematodinium perezi, negatively impacts the commercially important blue crab, Callinectes sapidus. The parasite is a host generalist, but it has not been reported from littoral fiddler crabs living within a few meters of habitat known to harbor infected blue crabs. In the first study, populations of three species of fiddler crab were screened for natural infections. The infection status of field-collected and lab-inoculated crabs was determined by screening fresh hemolymph with a 0.3% neutral red solution. Fiddler crabs were collected by hand in an area adjacent to where infected blue crabs were commonly collected. None of the 431 fiddlers had natural infections. In two separate studies, three species of fiddler crabs, Uca minax, U. pugnax, and U. pugilator, were evaluated for their susceptibility to H. perezi via inoculation of trophic stages. Uca minax inoculated with 10,000 cells of H. perezi were monitored for progression of the parasite. During hemolymph screenings of disease progression, filamentous trophonts, ameboid trophonts, and clump colonies were observed, indicative of active infections. In the second study, the minimum infective dose in U. minax was investigated. Fiddler crabs were inoculated with 0, 100, 1000, or 10,000 cells per crab. The minimum dose was determined to be approximately 1000 ameboid trophonts per crab. All three species of fiddler crab were susceptible to H. perezi via inoculation. The parasite was serially transferred from fiddler crabs to blue crabs without loss of infectivity. Survival studies indicated similar progression patterns to those observed in blue crabs. Based on our results fiddler crabs can serve as a laboratory model for investigating H. perezi infections and may be useful for comparative studies with blue crabs.

Molecular cloning reveals co-occurring species behind red tide blooms of the harmful dinoflagellate Cochlodinium polykrikoides

Red tides caused by the marine dinoflagellate Cochlodinium polykrikoides Margalef pose significant environmental problems worldwide. Recently, the existence of severe blooms attributable to a single Cochlodinium Schütt species has been questioned by many researchers. Herein we investigated the dinoflagellate composition of harmful algal blooms (HABs) attributed to C. polykrikoides in Korean coastal waters at nine different stations (St.). The component species of Cochlodinium blooms were examined by using microscopic and gene-cloning methods. In the nine study areas, C. polykrikoides was the predominant species of HABs in St. 2, 4, 7, and St. 9. Based on the morphological identification, the bloom was initially thought to be caused only by C. polykrikoides; however, we detected additional bloom-forming dinoflagellates (Polykrikos schwartzii Bütschli and Polykrikos kofoidii Chatton), and diatoms (Pseudo-nitzschia americana (Hasle) Fryxell) along with C. polykrikoides. The parasitic dinoflagellates Amoebophrya Koeppen and Euduboscquella Coats, Bachvaroff & Delwiche were found to be co-located with Cochlodinium in our study, and for the first time, Cochlodinium fulvescens Iwataki, Kawami & Matsuoka was detected in Korea (west coast). These results suggest co-existence of multiple dinoflagellates in bloom populations of Cochlodinium and describe the composition of other dinoflagellate blooms (e.g., Polykrikos spp.) in Korean coastal regions. This co-occurrence may be considered during efforts to monitor and control HABs.

Genetic Variations of the Parasitic Dinoflagellate Hematodinium Infecting Cultured Marine Crustaceans in China

The parasitic dinoflagellate Hematodinium infects multiple cultured marine crustaceans and has resulted in significant economic losses to their aquaculture in China. Limited molecular data implied a close relationship among Hematodinium reported in China, whereas the genetic diversity and detailed genetic variation within Hematodinium remains unclear. In order to investigate the genetic diversity and composition of the parasitic dinoflagellate in China, the sequences of the internal transcribed spacer region (ITS1 - 5.8S - ITS2) were amplified from 104 infected hosts cultured in three geographic locations. Two strains were identified, Hematodinium perezi II was the prevalent strain observed in all three host taxa throughout the survey, the other novel one was detected from the single Exopalaemon carinicauda collected from Zhejiang province. Eight ITS haplotypes within H. perezi II were identified with a similarity of 99.8% -100%. The distinct haplotype compositions and AMOVA analysis suggested a significant genetic differentiation and population structure among the three geographic populations of H. perezi II. The novel strain, genetically affiliated with H. perezi, was quite divergent from the three known genotypes (I, II and III) of H. perezi, and further investigation is needed to determine the distribution and host range of this new strain.

The bitter crab syndrome in commercial crabs in the Western part of the Bering and Chukchi Seas

We studied the distribution of the “bitter-crab” syndrome, a disease caused by the parasitic dinoflagellate Hematodinium sp., in eight commercial species of crabs in the west of the Bering and Chukchi seas. The crabs (25 388 individuals) were sampled during bottom trawl surveys of July‒September 2010 and October‒November 2012. The disease was first identified visually by a color change of the exoskeleton and the hemolymph of the animals and then using microscope analysis of hemolymph samples. Infestation was detected in crabs of three species, Chionoecetes opilio, C. bairdi, and Paralithodes platypus. The prevalence of the disease (the percent of infected individuals relative to all of those examined) in C. bairdi and P. platypus was very low, 0.1 and 0.3%, respectively. Infestation was widespread among C. opilio, its peak in the Bering Sea was in the fall. The average prevalence of the crab disease in different areas of the Bering Sea ranged from 0.8 to 10.8%. A high rate of crab infection was recorded in the Korfa Bay. In the Chukchi Sea, the average prevalence was 2%. Infestation by Hematodinium sp. was not revealed in the deep-sea snow crabs Chionoecetes tanneri and C. angulatus, and in three species of lithodid crabs, Paralithodes camtschaticus, P. brevipes, and Lithodes couesi. This can be explained by the small sample volume and/or ecology of these species, since the disease was registered in other areas in four of them.

Characterization of a new chytrid species parasitic on the dinoflagellate, Peridinium gatunense

Only a few chytrid fungi have been reported as parasites of dinoflagellates. Among these reports, chytrids are periodically observed growing on the dinoflagellate, Peridinium gatunense, in Lake Kinneret (Sea of Galilee), Israel. Because of the distinctive roles of parasitic chytrid fungi in decreasing phytoplankton populations and in transforming inedible algae into chytrid biomass which zooplankton grazers can eat, characterizing dinoflagellate parasites contributes to our understanding of the sustainability of this important water resource. An undescribed chytrid parasite of P. gatunense from Lake Kinneret has recently been brought into pure culture (KLL_TL-060613), facilitating exploration of its infection process. To evaluate the ability of this chytrid to affect host populations, we determined the effect of: (1) temperature and light (or dark) on prevalence of infection and (2) host growth phase and parasite:host ratio on percentage of infection. The greatest amplification in host infection occurred in cultures grown in the dark at 25 C. The percentage of host cells infected increased as the availability of host cells compared to parasite cells increased. These results demonstrate that environmental factors influence the chytrid’s potential to affect Peridinium gatunense populations. Because this chytrid had not been described taxonomically, we characterized its thallus morphology, development, zoospore ultrastructure and phylogenetic relationships. Zoospore ultrastructure was compatible with the Group II type zoospore characteristic of the family Chytridiaceae in the Chytridiales. Consistent with this observation, phylogenetic analyses of nuc 28S rDNA D1-D3 domains (28S) placed the chytrid in a clade among described taxa in the Chytridiaceae. Because thallus morphology was distinct from these other taxa, as well as other described parasites of dinoflagellates, this chytrid is described as a new genus and species, Dinochytrium kinnereticum.

Molecular characterization of a novel nitric oxide synthase gene from Portunus trituberculatus and the roles of NO/O2(-)- generating and antioxidant systems in host immune responses to Hematodinium.

Increasing evidences have established that the nitric oxide synthase (NOS) and NADPH oxidase (NOX) play important roles in host defense system by catalyzing the production of nitrogen oxide (NO) and superoxide anions (O2(-)), respectively. While, there are limited studies to explore the roles of NOS/NOX enzymes in crustacean immunity, and no studies as yet were attempted to elucidate their functions in host immune responses to parasites. In the present study, we cloned a full-length cDNA of NOS and two partial cDNA fragments of NOX and GPx from the economic valuable crab Portunus trituberculatus. The full-length cDNA of NOS was 4002 bp in length that encoded 1203 amino acids containing motifs of the NOS protein and conserved domains. The phylogenetic analysis showed that the NOS protein sequence was clustered together with those of crustacean species in the phylogenetic tree. All of the three novel genes showed high mRNA transcripts in the immune-related tissues (e.g. hemocytes, hepatopancreas) of P. trituberculatus. Striking fluctuation in the transcripts of the critical NO/O2(-)- generating/scavenging related genes (NOS, NOX, CuZnSOD, CAT, GPx) as well as in the enzymatic activities of NOS, NOX, SOD, CAT and GPx were observed in the hemocytes and hepatopancreas of P. trituberculatus post challenged with the parasitic dinoflagellate Hematodinium, indicating that the NO/O2(-)- generating and the antioxidant systems played vital roles in the crustacean innate immunity against the parasitic intrusion. The results indicated a novel respect of the host-parasite interaction between the crab host and the parasitic dinoflagellate Hematodinium.

Zoosporic parasites infecting marine diatoms - A black box that needs to be opened.

Living organisms in aquatic ecosystems are almost constantly confronted by pathogens. Nevertheless, very little is known about diseases of marine diatoms, the main primary producers of the oceans. Only a few examples of marine diatoms infected by zoosporic parasites are published, yet these studies suggest that diseases may have significant impacts on the ecology of individual diatom hosts and the composition of communities at both the producer and consumer trophic levels of food webs. Here we summarize available ecological and morphological data on chytrids, aphelids, stramenopiles (including oomycetes, labyrinthuloids, and hyphochytrids), parasitic dinoflagellates, cercozoans and phytomyxids, all of which are known zoosporic parasites of marine diatoms. Difficulties in identification of host and pathogen species and possible effects of environmental parameters on the prevalence of zoosporic parasites are discussed. Based on published data, we conclude that zoosporic parasites are much more abundant in marine ecosystems than the available literature reports, and that, at present, both the diversity and the prevalence of such pathogens are underestimated.

Complex Ancestries of Isoprenoid Synthesis in Dinoflagellates.

Isoprenoid metabolism occupies a central position in the anabolic metabolism of all living cells. In plastid-bearing organisms, two pathways may be present for de novo isoprenoid synthesis, the cytosolic mevalonate pathway (MVA) and nuclear-encoded, plastid-targeted nonmevalonate pathway (DOXP). Using transcriptomic data we find that dinoflagellates apparently make exclusive use of the DOXP pathway. Using phylogenetic analyses of all DOXP genes we inferred the evolutionary origins of DOXP genes in dinoflagellates. Plastid replacements led to a DOXP pathway of multiple evolutionary origins. Dinoflagellates commonly referred to as dinotoms due to their relatively recent acquisition of a diatom plastid, express two completely redundant DOXP pathways. Dinoflagellates with a tertiary plastid of haptophyte origin, by contrast, express a hybrid pathway of dual evolutionary origin. Here, changes in the targeting motif of signal/transit peptide likely allow for targeting the new plastid by the proteins of core isoprenoid metabolism proteins. Parasitic dinoflagellates of the Amoebophyra species complex appear to have lost the DOXP pathway, suggesting that they may rely on their host for sterol synthesis.