Marine actinomycetes related to the "Salinospora" group from the Great Barrier Reef sponge Pseudoceratina clavata.

Ten strains identified as marine actinomycetes related to the "Salinospora" group previously reported only from marine sediments were isolated from the Great Barrier Reef marine sponge Pseudoceratina clavata. The relationship of the isolates to "Salinospora" was confirmed by phylogenetic analysis of 16S rRNA gene sequences. Colony morphology and pigmentation, occurrence and position of spores, and salinity requirements for growth were all consistent with this relationship. Genes homologous to beta-ketosynthase, an enzyme forming part of a polyketide synthesis complex, were retrieved from these isolates; these genes shared homology with other Type I ketosynthase genes, and phylogenetic comparison with amino acid sequences derived from database beta-ketosynthase genes was consistent with the close relationship of these isolates to the actinomycetes. Primers based on 16S rRNA gene sequences and designed for targeting amplification of members of the "Salinospora" group via polymerase chain reaction have been used to demonstrate occurrence of these actinomycetes within the sponge tissue. In vitro bioassays of extracts from the isolates for antibiotic activity demonstrated that these actinomycetes have the potential to inhibit other sponge symbionts in vivo, including both Gram-negative and Gram-positive bacteria.