The cetacean microbiome is the group of communities of microorganisms that reside within whales.
Microbiomes play an important role in individual health and ecology and in particular in the discovery of different microbiomes in gut, skin and nose permitted to analyze their conditions and the condition of the marinMicrobiomee environment in which they live.
Gut
The access of microbial samples from the gut out of marine mammals is limited because most species are rare, endangered, and deep divers. There are different techniques for sampling the cetacean's gut microbiome. The most common is collecting fecal samples from the environment and taking a probe from the center that is non-contaminated. Besides there are studies from rectal swabs and rare studies from stranded dead or living animals direct from the intestine.
The intestinal microbiome of Cetaceans is a complex ecosystem that plays an important role in the metabolism, health, and immunity of the host. The microbial communities of marine mammals are diverse and distinct from terrestrial mammals, and the community depends on different factors like kind of diet, phylogeny, health, and age.
As the microbiome is involved in the decomposition of food, diet is a predominant factor for the microbial community. Different studies have shown that members of Bacteroidetes and Firmicutes are the most abundant phyla of gut microorganisms in animals that are cephalopod predators or zooplankton predators like in short-finned pilot whales and baleen whales. Especially the genus Bacteroides (phyla Bacteroidetes) seems to play a major role in the decomposition of the chitin-rich diet of these species and were also found in the gut microbiome of baleen whales.
In toothed cetacean species which food consumption is mainly piscivore the most abundant phyla are Firmicutes, Fusobacteria, and Proteobacteria. Proteobacteria are classified as a minor important group for marine mammals that consume cephalopods and zooplankton but are highly abundant in piscivorous predators like bottlenose dolphins, East Asian finless porpoises, and belugas. These findings could mirror the different dietary niches of these species.
Besides the dietary also the age seems to determine the differences in the microbial community between cetaceans. Maron et al. have shown that the microbial community is changing in right whale caves during their development. Interestingly the genera Bilophila, Peptococcus, and Treponema are more abundant in older calves. The higher abundance of Bilophila might be a response to the greater milk intake of the older calves.
Skin
The skin is the first barrier that protects the individual from the outside world and the epidermal microbiome on it is considered an indicator not only of the health of the animal but is also considered an ecological indicator that shows the state of the surrounding environment. Knowing the microbiome of the skin of marine mammals under ''normal'' conditions has allowed us to understand how these communities are different from the free microbial communities found in the sea and how they can change according to abiotic and biotic variations, and also ''communities vary between healthy and sick individuals''.
Different studies on migratory marine mammals in particular Megaptera novaeangliae, killer whales, Orcinus orca, and Beluga whales, which are exposed to different habitats host different communities of Bacterioplankton and in many cases diatoms growing on the backs of migrating killer whales.
Although studies on the microbiome of the skin of these marine mammals are quite limited, thanks to the amplification of SSU rRNA genes, were discovered communities belonging to the phylum Bacteroidetes, in particular of the family Flavobacteriaceae, the genus Tenacibaculum dicentrarchi, and it seems that the role of these bacteria is to regulate the microbiome present on the skin of marine mammals, acting as predators and limit the exponential growth of other communities.
Another type of bacterium found on the skin of cetaceans is Phychrobacter, able to tolerate low temperatures and therefore present during migratory routes to high latitudes, it was also discovered that this bacterium is one of those controlled by T. dicentrarchi; while in skin lesions the bacterium spp. Moraxella was found, but not only also in healthy skin such as blowholes and mouths of dolphins