ERWIN, P M; THACKER, R W; University of Alabama at Birmingham; University of Alabama at Birmingham: Cyanobacteria and Green Non-Sulfur Bacteria Described from Verongid Sponges: Patterns of Host-Specificity

Marine sponges harbor a diverse microbial community consisting largely of uncultured bacteria that are only beginning to be described using molecular and genetic techniques. We examined the diversity of cyanobacterial symbionts in 15 verongid sponges, representing 7 species, 4 genera, and 2 families. Bacterial 16S ribosomal DNA was amplified from whole sponge genomic extracts. For each sponge specimen, 10 clones of 16S rDNA were isolated, amplified, and digested using 2 restriction enzymes. Ten unique banding patterns resulted from restriction enzyme digests. Preliminary sequencing results indicate that 2 of the banding patterns correspond to the cyanobacterium Synechococcus sp. and a Chloroflexi (green non-sulfur) bacterial group. The Synechococcus sp. described here appears to be the only cyanobacterium associated with these verongid sponges and is genetically similar to previously identified Synechococcus isolated from other marine sponges. In phylogenetic analyses, the sponge-associated Synechococcus sequences form a distinct clade that shows 5.7-7.8% sequence divergence from their free-living counterparts. The Chloroflexi bacterial group described from verongid sponges includes a previously described sponge-associated bacterium and forms a distinct clade that shows 14.4-19.3% sequence divergence from the most closely related Chloroflexi. Both symbionts described here are genetically distinct from their free-living relatives, suggesting that the sponge mesohyl matrix is a unique microenvironment for symbiotic microorganisms. Although each group of these symbionts forms a distinct clade, there is little evidence for host-specific associations within the clades.