Hidden in the blow - a matrix to characterise cetaceans’ respiratory microbiome: short-finned pilot whale as case study

Cetaceans are key sentinel species of marine ecosystems and ocean health, being a strategic taxonomic group that evaluates the well-being of aquatic habitats and detects harmful environmental trends. Respiratory diseases are amongst the main causes of death in these animals, so identifying the microbiome community in their exhaled breath condensates (EBC), i.e. blow, has been proposed as a key biomarker for assessing respiratory health. Yet, to characterise microbiomes related to these animals' respiratory tract and use them as a proxy for health status, it is necessary to develop baseline data on the microorganisms associated with cetaceans. Here, the short-finned pilot whale (SFPW, Globicephala macrorhynchus) was used as a case study to validate the most suitable primer set to explore the prokaryotic diversity of the cetaceans' respiratory tract. DNA extracted from blow samples (n = 12) of animals off Madeira Island was sequenced to amplify both V3-V4 and V4-V5 hypervariable regions of the 16S rRNA gene, using the same sequencing platform (Illumina MiSeq). Independently of the primer set used, all blows shared Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria phyla in their composition. V3-V4 resulted in a higher diversity of taxa with relative abundance above 1%, whereas the V4-V5 primers captured a higher number of microbial Amplicon Sequence Variants, detecting the rare microbial biosphere with pathogen potential. Additionally, it captured the core microbiome more efficiently. Thus, this study provides a detailed characterisation of SFPW respi- ratory-associated microbial communities, strengthening the idea of sociality influencing microbiome composition in the respiratory tract. Moreover, it supports the use of blow as a relevant biomarker for the physiological state of the airways in free-ranging cetaceans.