Abstract
Associations of freshwater sponges with coccoid green algae have been known for a long time. Two types of coccoid green algae, which are commonly assigned as zoochlorellae, are recognized by morphology: small coccoids (< 3 μm) without pyrenoids and larger Chlorella-like algae (4–6 μm) with pyrenoids. Despite their wide distribution in some freshwater sponges, these green algae were never studied using a combined analysis of morphology and molecular phylogeny. We investigated several endosymbiotic strains isolated from different Spongilla species, which were available in culture collections. Phylogenetic analyses of SSU and ITS rDNA sequences revealed that the strain SAG 211-40a is a member of the Chlorellaceae and represents a new species of the newly erected genus Lewiniosphaera, L symbiontica. The phylogenetic position was confirmed by morphology and ITS-2 barcode. The endosymbionts without pyrenoid were identified as Choricystis parasitica by morphology and phylogenetic analyses. The comparison with free-living strains revealed the recognition of two new Choricystis species, C. krienitzii and C. limnetica, which were confirmed by molecular signatures in V9 region of SSU rDNA and ITS-2 barcode.
Highlights
Marine and freshwater sponges (Porifera) commonly contain photosynthetic endosymbionts
SAG 211-40a and SAG 211-40b were the endosymbionts of Spongilla lacustris and S. fluviatilis (= Ephydatia fluviatilis) found in Cotuit and Manumet Beach (Lewin 1966)
All strains were identified as Choricystis minor (= C. parasitica according to Pröschold et al 2011)
Summary
Marine and freshwater sponges (Porifera) commonly contain photosynthetic endosymbionts. Connected with the fact that the endosymbionts need light for photosynthesis, they are only located in animals with colorless tissues or in organs and organelles exposed to sunlight. Most of marine sponges possess endosymbiotic cyanobacteria (coccoid or filamentous; Wilkinson 1992). Eukaryotic algae are less distributed in marine sponges.
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