The low diverse gastric microbiome of the jellyfish Cotylorhiza tuberculata is dominated by four novel taxa.

Cotylorhiza tuberculata is an important scyphozoan jellyfish producing population blooms in the Mediterranean probably due to pelagic ecosystem's decay. Its gastric cavity can serve as a simple model of microbial-animal digestive associations, yet poorly characterized. Using state-of-the-art metagenomic population binning and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), we show that only four novel clonal phylotypes were consistently associated with multiple jellyfish adults. Two affiliated close to Spiroplasma and Mycoplasma genera, one to chlamydial 'Candidatus Syngnamydia', and one to bacteroidetal Tenacibaculum, and were at least one order of magnitude more abundant than any other bacteria detected. Metabolic modelling predicted an aerobic heterotrophic lifestyle for the chlamydia, which were found intracellularly in Onychodromopsis-like ciliates. The Spiroplasma-like organism was predicted to be an anaerobic fermenter associated to some jellyfish cells, whereas the Tenacibaculum-like as free-living aerobic heterotroph, densely colonizing the mesogleal axis inside the gastric filaments. The association between the jellyfish and its reduced microbiome was close and temporally stable, and possibly related to food digestion and protection from pathogens. Based on the genomic and microscopic data, we propose three candidate taxa: 'Candidatus Syngnamydia medusae', 'Candidatus Medusoplasma mediterranei' and 'Candidatus Tenacibaculum medusae'.

Design, synthesis and antibacterial study of new potent and selective coumarin-chalcone derivatives for the treatment of tenacibaculosis.

With the aim of finding new chemical entities selective for fish pathogens to avoid drug resistance in humans, a series of coumarin-chalcone hybrid compounds with different patterns of substitution were designed and synthesized. Their antibacterial activity was evaluated against important types of human bacteria strains (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa) and against a fourteen strains of the marine pathogen Tenacibaculum maritimum, responsible for tenacibaculosis in fish, which is an important disease that causes great economical loss in the aquaculture industry. All the amino derivatives 5-12 presented high activity against different strains of T. maritimum, no activity against any of the three human pathogenic bacteria strains and no toxicity. Compounds 6, 7 and 11 were the most promising molecules. The most sensitive strains to these compounds were LL01 8.3.8 and LL01 8.3.1, being compound 11 up to 20 times more active than enrofloxacin. Therefore these scaffolds are good candidates for aquaculture treatments, avoiding possible drug resistance problems in humans.