The microbiome is the name for the collection of microbes that live on or in another organism. The human microbiome has received a lot of attention, but in fact every living thing hosts a community of microbes that can be helpful—even vital—or sometimes harmful. In this study, we investigated the microbiome of tuna to identify the specific bacteria that populate it and whether the microbiome varies depending on the type of tuna, the ocean it lives in, or the organ. We found that the gut microbiome differs according to species due to feeding habits, while the skin microbiome differs according to the environment and is linked to the bacteria in the surrounding seawater. Bacteria that can cause food poisoning in humans were concentrated in the gut and liver of tuna, highlighting the importance of removing the organs before consuming this fish, which is one of the most widely eaten in the world.

Background : Although tunas represent a significant part of the global fish economy and a major nutritional resource worldwide, their consumption poses a risk of food poisoning through the development of particular bacterial pathogens. However, their microbiome still remains poorly documented. Here, we conducted a multi-compartmental analysis of the taxonomic composition of the bacterial communities inhabiting the gut, skin and liver of two most consumed tropical tuna species (skipjack and yellowfin), from individuals caught in the Atlantic and Indian oceans. Results : Our results revealed that the composition of the microbiome was independent of fish sex, regardless of the species and ocean considered. Instead, the main determinants were (i) tuna species for the gut and(ii) sampling site for the skin mucus layer, and (iii) a combination of both parameters for the liver. Interestingly, only 4.5% of all ASVs were shared by the three compartments, raising numerous questions about the circulation of microorganisms within the tuna body. Our results also revealed the presence of a unique and diversified bacterial assemblage within the liver, comprising a substantial proportion of histamine-producing bacteria, well known for their potential pathogenicity and their contribution to fish poisoning cases. Conclusions : These results indicate that the tuna liver is an unexplored microbial niche whose role in the health of both the host and consumers remains to be elucidated.

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