Common core respiratory bacteriome of the blue whaleBalaenoptera musculus, in the Gulf of California

Abstract The number of strandings and unusual mortality events that involve cetaceans may have increased, and potential pathogens of the respiratory tract have been found during the examination of individuals in many of these events. However, investigating the health of free-ranging large whales is logistically complex. Given that the core microbiome is key to understanding host-bacteria relationships and to identifying their relevance for individual and population health, we characterized the core respiratory bacteriome of the Eastern North Pacific blue whale, Balaenoptera musculus , using blow samples collected by a small quadracopter drone. 16S rRNA gene high-throughput sequencing revealed 1,326 amplicon sequence variants (ASVs), of which 11 were shared by more than 50% of all blue whales and had a relative abundance higher than 0.02%. Cutibacterium, Oceanivirga, Tenacibaculum , and Psychrobacter composed the common core respiratory bacteriome of the blue whale. Additionally, compositional analysis identified 15 bacterial classes dominated by Gammaproteobacteria (27.14%), Bacteroidea (19.83%), and Clostridia (12.89%) as the most representative classes in the respiratory tract of blue whales. However, two whales had a high abundance of bacteria with pathogenic potential, namely M ycoplasma spp. and Streptococcus spp. in their blow. Both bacterial genera have been associated with pulmonary diseases in mammals. Ours is the first study to characterize the respiratory bacteriome of apparently healthy blue whales and is a baseline for future long-term studies on blue whale health, an endangered species of conservation concern.