Pyrosequencing and culturing of Hawaiian corticolous biofilms demonstrate high diversity and confirm phylogenetic placement of the green alga Spongiochrysis hawaiiensis in Cladophorales (Ulvophyceae)

Spongiochrysis hawaiiensis, a terrestrial green alga found in subaerial biofilms along the windward coast of O'ahu, was originally described as a member of the Cladophorales, a primarily marine and freshwater order, based on DNA sequence data. However, a subsequent report allied this taxon with the entirely terrestrial order Trentepohliales. Yet biofilm communities may contain multiple species of green algae, and sequences from both studies were generated from uncultured environmental samples using Sanger sequencing, rendering these results uncertain. In the current study, pyrosequencing of the SSU rDNA gene was used to determinate the algal species composition of these communities, and Sanger sequences of unialgal cultures were generated to unambiguously determine the phylogenetic placement of S. hawaiiensis. Results of the current study indicated that communities were composed primarily of 'cladophoralean S. hawaiiensis'; numerous trentepohlialean taxa, including one that formed a clade with the previously published 'trentepohlialean S. hawaiiensis'; and members of the Trebouxiophyceae. Abundances of the 'cladophoralean S. hawaiiensis' and the most abundant trentepohlialean taxon were too similar to determine which was the dominant member of the community based on pyrosequencing data alone. Phylogenetic analysis of Spongiochrysis SSU sequences from unialgal culture clearly allied the taxon within the Cladophorales, thus refuting the hypothesis that Spongiochrysis is a member of the Trentepohliales.