Phylogenetic and morphological characterisation of the green algae infesting blue musselMytilus edulisin the North and South Atlantic oceans

Abstract

Blue mussels Mytilus edulis with shell deformations and green pustules containing parasitic algae were collected at 3 coastal sites (Burøy, Norway; Bockholm, Denmark; Goose Green, Falkland Islands). A comparative study, including mussel histopathology, algal morphology, ultrastructure and phylogenetic position was performed. Green pustules were mainly located in the posterior portion of the mantle and gonad tissues and the posterior adductor muscle. Electron microscopy confirmed the presence of algal cells with similar morphology to Coccomyxa parasitica. Algae were oval shaped with a single nucleus and chloroplast, 1 or 2 mitochondria and a dense granular cytoplasm with a lipid inclusion body, Golgi apparatus and small vesicles. Partial small subunit (SSU) rRNA phylogeny confirmed the inclusion of parasitic algae into the Coccomyxa clade. However, the sequence identity between almost full SSU rRNA sequences of parasitic algae and others in this clade yielded an unexpected result. Green algae from mussels were distant from C. parasitica Culture Collection of Algae and Protozoa (CCAP) strain 216/18 (94% identity), but very similar (99% identity) to C. glaronensis (a lichen endosymbiont) and green endophytes from the tree Ginkgo biloba. The CCAP strain 216/18 was a sister sequence to Nannochloris algae, far from the Coccomyxa clade. These results suggest a misidentification or outgrowth of the original CCAP strain 216/18 by a different 'Nannochloris-like' trebouxiophycean organism. In contrast, our sequences directly obtained from infested mussels could represent the true C. parasitica responsible for the green pustules in blue mussels.

Photobiont association and genetic diversity of the optionally lichenized fungus Schizoxylon albescens

“…The genus is polyphyletic (Rodríguez et al, 2008) and includes free-living species, parasitic species of marine echinoderms, epiphytic or endophytic species of higher plants and lichen thalli, and lichen photobionts (Jaag, 1931;Honegger, 1991;Gray et al, 1999;Rodríguez et al, 2008). Also in our analysis of the nucSSU gene (Fig.…”

Molecular diversity of green corticolous microalgae from two sub-Mediterranean European localities

“…These microalgae are widely distributed in various terrestrial habitats (Ettl & Gärtner, 1995). In addition, they occur as lichen photobionts (Zoller & Lutzoni, 2003) and as parasites and endophytes of vascular plants and invertebrates (Rodríguez et al, 2008). Given their phylogenetic and ecological heterogeneity, they should probably be divided into several genera in the future.…”

Phylogeny and Molecular Evolution of the Green Algae

“…This symbiosis has been found to be facultative in lab conditions since both the Paramecium and the algae can be cultivated separately. Other eukaryotes that harbour green algal symbionts (including parasites) include fungi, dinoflagellates, foraminifers, radiolarians, sponges, marine flatworms, cnidarians, molluscs (nudibranchs and giant clams) and vertebrates (Parke & Manton, 1967;Sweeney, 1976;Cachon & Caram, 1979;Williamson, 1979;Friedl & Bhattacharya, 2002;Lewis & Muller-Parker, 2004;Rodriguez et al, 2008;Kovacevic et al, 2010;Nowack & Melkonian, 2010;Kerney et al, 2011). As yet, it remains unclear whether these associations have resulted in endosymbiont-to-host gene transfer.…”