Assessing and optimising culturing methods for the associated-bacteria of two species of deep-sea sponges (class Hexactinellida) for antimicrobial bioprospecting

There is a need for novel classes of antimicrobials to be discovered in order to tackle the growing challenges of antimicrobial resistance. Deep-sea sponges are drawing much attention due to the phylogenetically diverse and dense communities of microbes that live within their tissues. Bioprospecting these sponges offers the possibility of exploring a niche environment that could contain novel classes of antimicrobials. To assess the suitability of Pheronema carpenteri (class Hexactinellida, order Amphidiscosida) and Rhabdodictyum sp. (class Hexactinellida, order Lyssacinosida) as a source of antimicrobials, cultivation-dependent strategies were employed. We assess the culturability of sponge-associated bacterial from P. carpenteri (n=3) and Rhabdodictyum sp. (n=2) using8 treatments; 4 temperature incubation treatments (4, 15, 22–25 and 28 °C), nutritional additives (Sponge spicule extract and a low nutrient heterotrophic media additive), and finally a 24 h enrichment stage. Recovered isolates were screen recovered sponge associated-bacteria isolates for bioactivity against Escherichia coli and Micrococcus luteus. Isolates demonstrating high activity were then tested against 7 clinically relevant pathogens; Staphylococcus aurerus 6571, Streptococcus pyogenes, E. coli 1077, Salmonella enterica Serovar Typhimurium LT2, Klebsiella pneumonia 681, Mycoccoccus phlei and Candida albicans. More isolates were recovered from Rhabdodictyum sp. than P. carpenteri (P<0.005). Isolates recovered from P. carpenteri demonstrate high antibacterial activity against both Gram-positive and Gram-negative strains. 112 isolates in total were found to be bioactive against M. luteus, 55 of which were active against both M. luteus and E. coli. The highest potion of bioactive compounds derived from a 15°C treatment and from the inclusion of Sponge Spicule Extract as a nutritional additive. This research presents the first attempts of bioprospecting these two species of deep-sea sponges and thus far has shown promise in their suitability.