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.