Ten Ostreobium (Ulvophyceae) strains from Great Barrier Reef corals as a resource for algal endolith biology and genomics

Ostreobium is a genus of siphonous green algae that lives as an endolith in carbonate substrates under extremely limited light conditions and has recently been gaining attention due to its roles in reef carbonate budgets and its association with reef corals. Knowledge about this genus remains fairly limited due to the scarcity of strains available for physiological studies. Here, we report on 10 strains of Ostreobium isolated from coral skeletons from the Great Barrier Reef. Phenotypic diversity showed differences in gross morphology and in a few structures. Phylogenetic analyses of the tufA and rbcL put the strains in the context of the lineages identified previously through environmental sequencing. The chloroplast genomes of our strains are all around 80 kbp in length and show that genome structure is highly conserved, with only a few insertions (some containing putative protein-coding genes) differing between the strains. The addition of these strains from the Great Barrier Reef to our toolkit will help develop Ostreobium as a model species for endolithic growth, low-light photosynthesis and coral-algal associations.