Specific antibacterial activity against potential pathogens and re- straining of larvae settlement from a pigmented Pseudoalteromonas strain isolated from the jellyfish Cassiopea xamachana

The bacterial genus Pseudoalteromonas is commonly found in the ocean and frequently associated with marine invertebrates. This bacterial group produces metabolites with antibacterial, algicidal, antifouling, and biofilm promoting activities that have interested the scientific community for years. Unlike corals, reports on diseased symbiotic, soft-body cnidarians are scarce, suggesting their surface mucus layer may be efficient in fighting potential bacterial pathogens. With the aim to study attributes of cnidaria-associated bacteria, we isolated a Pseudoalteromonas pigmented strain from the surface mucus layer of a bleached jellyfish Cassiopea xamachana with a 99,66% similarity to P. piscicida, as identified through 16S rRNA sequencing. This Pseudoalteromonas sp. yellow isolate specifically inhibited the growth of the potential bacterial pathogen Serratia marcescens, and an Aurantimonas sp. strain. This isolated Pseudoalteromonas strain also showed activity against epibionts, reducing the settlement of medusa larvae by 50% compared to controls. A 40% inhibition in the settlement of medusa larvae was scored for an organic extract prepared from a filtrate of the cultured isolate as well as positive protease activity. Overall, our results suggest Pseudoalteromonas sp. yellow isolate can fight potential pathogens and produce extracellular vesicles with metabolites that can influence the settlement and survival of larvae, presenting positive attributes for this animal host.