Diversity and antimicrobial activities of microbes from two Irish marine sponges, Suberites carnosus and Leucosolenia sp

Aims: To evaluate the diversity and antimicrobial activity of bacteria from the marine sponges Suberites carnosus and Leucosolenia sp. Methods and Results: Two hundred and thirty‐seven bacteria were isolated from the sponges S. carnosus (Demospongiae) and Leucosolenia sp. (Calcarea). Isolates from the phyla Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria were obtained. Isolates of the genus Pseudovibrio were dominant among the bacteria from S. carnosus, whereas Pseudoalteromonas and Vibrio were the dominant genera isolated from Leucosolenia sp. Approximately 50% of the isolates from S. carnosus displayed antibacterial activity, and c. 15% of the isolates from Leucosolenia sp. demonstrated activity against the test fungal strains. The antibacterial activity observed was mostly from Pseudovibrio and Spongiobacter isolates, while the majority of the antifungal activity was observed from the Pseudoalteromonas, Bacillus and Vibrio isolates. Conclusions: Both sponges possess a diverse range of bioactive and potentially novel bacteria. Differences observed from the sponge‐derived groups of isolates in terms of bioactivity suggest that S. carnosus isolates may be a better source of antibacterial compounds, while Leucosolenia sp. isolates appear to be a better source of antifungal compounds. Significance and Impact of the Study: This is the first study in which cultured bacterial isolates from the marine sponges S. carnosus and a Leucosolenia sp. have been evaluated for their antibacterial activity. The high percentage of antibacterial isolates from S. carnosus and of antifungal isolates from Leucosolenia sp. suggests that these two sponges may be good sources for potentially novel marine natural products.