Identification of Chromera velia by fluorescence in situ hybridization

New trichrome stains identify cysts of Colpodella sp. (Apicomplexa) and Bodo caudatus

Colpodella species are free-living close relatives of apicomplexans that were recently reported to cause red blood cell infection in an immunocompromised human host and in a tick-borne human infection resulting in neurological symptoms. Unambiguous identification of the life cycle stages of Colpodella sp. using routine stains for light microscopy will aid rapid diagnosis in infections. Similarly, cells in culture and environmental samples can be rapidly identified by staining. Staining protocols are currently unavailable for cell detection by light microscopy. In this study, we investigated the feasibility of performing routine staining techniques for light microscopy for differentiating Colpodella sp. (ATCC 50594) and Bodo caudatus cysts in Hay medium cultures. We tested different basic and acidic dyes alone and in combination and also utilized a commercial trichrome staining protocol. The nonspecific fluorescent dye Calcofluor white was also evaluated. Staining times, dye concentrations, use of tap or distilled water rinses, use of a mordant and inclusion, or omission of decolorizers after staining were evaluated. We compared the intensity of color, clarity of morphological features, and cytoplasmic structures detected after staining. We report a new trichrome staining technique that allowed clear identification and differentiation of cyst stages of Colpodella sp. and B. caudatus. Immature Colpodella sp. cysts were identified as having an irregular, dual-colored (demilune), dark blue-purple and white appearance. Mature Colpodella sp. cysts stained dark red-blue and were identified in four-way mitotic division, while cysts of B. caudatus in diprotist or monoprotist (ATCC 30905) cultures were detected as spherical and red-pink in appearance.

Combined amplicon pyrosequencing assays reveal presence of the apicomplexan "type-N" (cf. Gemmocystis cylindrus) and Chromera velia on the Great Barrier Reef, Australia

Background

The coral is predominantly composed of the metabolically dependent coral host and the photosynthetic dinoflagellate Symbiodinium sp. The system as a whole interacts with symbiotic eukaryotes, bacteria and viruses. Gemmocystiscylindrus (cf. “type-N” symbiont) belonging to the obligatory parasitic phylum Apicomplexa (Alveolata) is ubiquitous in the Caribbean coral, but its presence in the Great Barrier Reef coral has yet to be documented. Approaches allowing identification of the healthy community from the pathogenic or saprobic organisms are needed for sustainable coral reef monitoring.

Methods & Principal Findings

We investigated the diversity of eukaryotes associated with a common reef-building corals from the southern Great Barrier Reef. We used three tag encoded 454 amplicon pyrosequencing assays targeting eukaryote small-subunit rRNA gene to demonstrate the presence of the apicomplexan type-N and a photosynthetic sister species to Apicomplexa - Chromeravelia. Amplicon pyrosequencing revealed presence of the small-subunit rRNA genes of known eukaryotic pathogens (Cryptosporidium and Cryptococcus). We therefore conducted bacterial tag encoded amplicon pyrosequencing assay for small-subunit rRNA gene to support effluent exposure of the coral. Bacteria of faecal origin (Enterobacteriales) formed 41% of total sequences in contrast to 0-2% of the coral-associated bacterial communities with and without C. velia, respectively.

Significance

This is the first time apicomplexan type-N has been detected in the Great Barrier Reef. Eukaryote tag encoded amplicon pyrosequencing assays demonstrate presence of apicomplexan type-N and C. Velia in total coral DNA. The data highlight the need for combined approaches for eukaryotic diversity studies coupled with bacterial community assessment to achieve a more realistic goals of defining the holobiont community and assessing coral disease. With increasing evidence of Apicomplexa in coral reef environments, it is important not only to understand the evolution of these organisms but also identify their potential as pathogens.

Cell biology of chromerids: autotrophic relatives to apicomplexan parasites

Chromerida are algae possessing a complex plastid surrounded by four membranes. Although isolated originally from stony corals in Australia, they seem to be globally distributed. According to their molecular phylogeny, morphology, ultrastructure, structure of organellar genomes, and noncanonical pathway for tetrapyrrole synthesis, these algae are thought to be the closest known phototrophic relatives to apicomplexan parasites. Here, we summarize the current knowledge of cell biology and evolution of this novel group of algae, which contains only two formally described species, but is apparently highly diverse and virtually ubiquitous in marine environments.