Evolution and diversity of the Golgi body

Often considered a defining eukaryotic feature, the Golgi body is one of the most recognizable and functionally integrated cellular organelles. It is therefore surprising that some unicellular eukaryotes do not, at first glance, appear to possess Golgi stacks. Here we review the molecular evolutionary, genomic and cell biological evidence for Golgi bodies in these organisms, with the organelle likely present in some form in all cases. This, along with the overwhelming prevalence of stacked cisternae in most eukaryotes, implies that the ancestral eukaryote possessed a stacked Golgi body, with at least eight independent instances of Golgi unstacking in our cellular history.     

FISH probes for the detection of the parasitic dinoflagellate Amoebophrya sp. infecting the dinoflagellate Akashiwo sanguinea in Chesapeake Bay

A comparison of the small subunit rRNA sequences of a Chesapeake Bay strain of the dinoflagellate Akashiwo sanguinea and the dinoflagellate Amoebophrya sp. parasitizing it revealed several potential target sites that could be used to detect the parasite through in situ hybridization. The fluorescence of probed cells under various conditions of hybridization was measured by using a spot meter on a Nikon UFX-II camera attachment so that the effect of various hybridization parameters on probe binding could be determined. Probes directed against both the junction between helices 8 and 11 and helix 46 could detect the parasite, although the helix 8/11 probe produced a stronger signal under the conditions tested. The fluorescence of the probed cells increased with increasing hybridization time up to approximately twelve hours. The background fluorescence was lower at the wavelengths used to detect Texas Red than at those used to detect fluorescein, so probed cells were more distinct when Texas Red was used as the label. Cells stored in cold paraformaldehyde for a year still bound the probes. Young stages of the parasite could be seen more readily after in situ hybridization than after protargol impregnation.     

An evolutionary balance: conservation vs innovation in ciliate membrane trafficking

As most of eukaryotic diversity lies in single‐celled protists, they represent unique opportunities to ask questions about the balance of conservation and innovation in cell biological features. Among free‐living protists the ciliates offer ease of culturing, a rich array of experimental approaches, and versatile molecular tools, particularly in Tetrahymena thermophila and Paramecium tetraurelia. These attributes have been exploited by researchers to analyze a wealth of cellular structures in these large and complex cells. This mini‐review focuses on 3 aspects of ciliate membrane dynamics, all linked with endolysosomal trafficking. First is nutrition based on phagocytosis and maturation of food vacuoles. Secondly, we discuss regulated exocytosis from vesicles that have features of both dense core secretory granules but also lysosome‐related organelles. The third topic is the targeting, breakdown and resorption of parental nuclei in mating partners. For all 3 phenomena, it is clear that elements of the canonical membrane‐trafficking system have been retained and in some cases repurposed. In addition, there is evidence that recently evolved, lineage‐specific proteins provide determinants in these pathways.      

Multiple strains of the parasitic dinoflagellate Amoebophrya exist in Chesapeake Bay

Small subunit rRNA sequences were amplified from Amoebophrya strains infecting Karlodinium micrum, Gymnodinium instriatum and an unidentified Scrippsiella species in Chesapeake Bay. The alignable parts of the sequences differed from each other and from the previously reported rRNA sequence of the Amoebophrya strain infecting Akashiwo sanguinea in Chesapeake Bay by 4 to 10%. This is a greater degree of difference than sometimes found between sequences from separate genera of free-living dinoflagellates. These sequence differences indicate that the Amoebophrya strains parasitizing dinoflagellates in Chesapeake Bay do not all belong to the same species. In spite of their relative dissimilarity, the sequences do group together into a single clade with high bootstrap support in phylogenetic trees constructed from the sequences.     

Inducible Mixotrophy in the Dinoflagellate Prorocentrum minimum

Prorocentrum minimum is a neritic dinoflagellate that forms seasonal blooms and red tides in estuarine ecosystems. While known to be mixotrophic, previous attempts to document feeding on algal prey have yielded low grazing rates. In this study, growth and ingestion rates of P. minimum were measured as a function of nitrogen (‐N) and phosphorous (‐P) starvation. A P. minimum isolate from Chesapeake Bay was found to ingest cryptophyte prey when in stationary phase and when starved of N or P. Prorocentrum minimum ingested two strains of Teleaulax amphioxeia at higher rates than six other cryptophyte species. In all cases ‐P treatments resulted in the highest grazing. Ingestion rates of ‐P cells on T. amphioxeia saturated at ~5 prey per predator per day, while ingestion by ‐N cells saturated at 1 prey per predator per day. In the presence of prey, ‐P treated cells reached a maximum mixotrophic growth rate (μ_max) of 0.5 d^?1, while ‐N cells had a μ_max of 0.18 d^?1. Calculations of ingested C, N, and P due to feeding on T. amphioxeia revealed that phagotrophy can be an important source of all three elements. While P. minimum is a proficient phototroph, inducible phagotrophy is an important nutritional source for this dinoflagellate.     

Species of the parasitic genus Duboscquella are members of the enigmatic Marine Alveolate Group I

Small subunit ribosomal RNA gene sequences of Duboscquella spp. infecting the tintinnid ciliate, Favella ehrenbergii, were determined. Two parasites were sampled from different localities. They are morphologically similar to each other and both resemble D. aspida. Nevertheless, two distinct sequences (7.6% divergence) were obtained from them. Phylogenetic trees inferred from maximum likelihood and maximum parsimony revealed that these two Duboscquella spp. sequences are enclosed in an environmental clade named Marine Alveolate Group I. This clade consists of a large number of picoplanktonic organisms known only from environmental samples from various parts of the ocean worldwide, and which therefore lack clear characterization and identification. Here, we provide morphological and genetic characterization of these two Duboscquella genotypes included in this enigmatic clade. Duboscquella spp. produce a large number of small flagellated spores as dispersal agents and the presence of such small cells partially explains why the organisms related to these parasites have been detected within environmental genetic libraries, built from picoplanktonic size fractions of environmental samples. The huge diversity of the Marine Alveolate Group I and the finding that parasites from different marine protists belong to this lineage suggest that parasitism is a widespread and ecologically relevant phenomenon in the marine environment.     

Alveolate phylogeny inferred using concatenated ribosomal proteins

Dinoflagellates and apicomplexans are a strongly supported monophyletic group in rDNA phylogenies, although this phylogeny is not without controversy, particularly between the two groups. Here we use concatenated protein-coding genes from expressed sequence tags or genomic data to construct phylogenies including "typical" dinophycean dinoflagellates, a parasitic syndinian dinoflagellate, Amoebophrya sp., and two related species, Oxyrrhis marina, and Perkinsus marinus. Seventeen genes encoding proteins associated with the ribosome were selected for phylogenetic analysis. The dataset was limited for the most part by data availability from the dinoflagellates. Forty-five taxa from four major lineages were used: the heterokont outgroup, ciliates, dinoflagellates, and apicomplexans. Amoebophrya sp. was included in this phylogeny as a sole representative of the enigmatic marine alveolate or syndinian lineage. The atypical dinoflagellate O. marina, usually excluded from rDNA analyses due to long branches, was also included. The resulting phylogenies were well supported in concatenated analyses with only a few unstable or weakly supported branches; most features were consistent when different lineages were pruned from the tree or different genes were concatenated. The least stable branches involved the placement of Cryptosporidium spp. within the Apicomplexa and the relationships between P. marinus, Amoebophrya sp., and O. marina. Both bootstrap and approximately unbiased test results confirmed that P. marinus, Amoebophrya sp., O. marina, and the remaining dinoflagellates form a monophyletic lineage to the exclusion of Apicomplexa.     

Dinoflagellate diversity and distribution

Dinoflagellates are common to abundant in both marine and freshwater environments. They are particularly diverse in the marine plankton where some cause “red tides” and other harmful blooms. More than 2,000 extant species have been described, only half of which are photosynthetic. They include autotrophs, mixotrophs and grazers. They are biochemically diverse, varying in photosynthetic pigments and toxin production ability. Some are important sources of bioluminescence in the ocean. They can host intracellular symbionts or be endosymbionts themselves. Most of the photosynthetic “zooxanthellae” of invertebrate hosts are mutualistic dinoflagellate symbionts, including all those essential to reef-building corals. Roughly 5% are parasitic on aquatic organisms. The fossil record, consisting of more than 2,500 species, shows a rapid radiation of cysts, starting in the Triassic, peaking in the Cretaceous, and declining throughout the Cenozoic. Marine species with a benthic, dormant cyst stage are confined to the continental shelf and fossil cysts can be used as markers of ancient coastlines. Northern and southern hemispheres contain virtually identical communities within similar latitudes, separated by a belt of circumtropical species. A few endemics are present in tropical and polar waters. Some benthic dinoflagellates are exclusively tropical, including a distinct phycophilic community, some of which are responsible for ciguatera fish poisoning. In lakes chemical and grazing effects can be important. Predatory dinoflagellates co-occur with their prey, often diatoms. Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.