The octocoral microbiome: from community structure and function to novel chitinases for the circular blue bioeconomy

Octocorals are an integral part of benthic marine ecosystems, increasing habitat complexity and biodiversity. They associate with diverse microorganisms, including micro-eukaryotes, prokaryotes, and viruses. Our previous research on temperate octocorals showed that their microbiome is distinct from the environmental surroundings, host genus-specific, and undergoes complex structural changes under dysbiosis [1]. However, the role of microbial symbionts that populate octocorals is still poorly understood. To shed light on their metabolic capacities, we examined 66 high-quality metagenome-assembled genomes (MAGs), spanning 30 prokaryotic species, retrieved from microbial metagenomes of three temperate octocoral species and seawater [2]. Symbionts affiliated with Endozoicomonadaceae, Candidatus Thioglobaceae, and Metamycoplasmataceae, among others. Phylogenomics showed that the Endozoicomonadaceae MAGs represent a novel genus unique to temperate octocorals, denoted Candidatus Gorgonimonas. These symbionts harboured chitinase and chitin-binging protein-encoding genes, indicating that they hydrolyse the most abundant polysaccharide in the ocean. Subsequent examination of >40 genomes of cultured and uncultured Endozoicomonadaceae strains demonstrated that chitinases and other genes involved in chitin degradation are widespread in the Endozoicomonadaceae family, suggesting that these symbionts play important roles in chitin turnover in marine invertebrates and benthic ecosystems [3]. Since Candidatus Gorgonimonas bacteria remain unculturable, we employed synthetic biology and heterologous expression to harness their enzymes. Two novel, active and mesophilic chitinases from octocoral symbionts were successfully produced, holding promise for upcycling of seafood waste as chitin(ase)-derived products find applications in multiple sectors, from biomedicine over the food industry to agriculture.

[1] Keller-Costa et al., 2021, Microbiome, 9 https://doi.org/10.1186/s40168-021-01031-y

[2] Keller-Costa et al., 2022, Microbiome, 10 https://doi.org/10.1186/s40168-022-01343-7

[3] da Silva,….,& Keller-Costa 2023 ISME COMMUN, 3 https://doi.org/10.1038/s43705-023-00316-7