Characterization of skin, cloacal, and respiratory-associated microbiota in Mediterranean loggerhead and Green Sea turtle populations

Abstract Animals are considered biological units with their microbiota, which is composed of commensal, pathogenic, and symbiont bacteria. This microbiota is shaped by the environment and through changes in the animal life history, and it plays a key role in the physiology and fitness of its host. Sea turtles are known to be good indicators of marine ecosystem health, and it is known that their populations are declining in the Mediterranean. Herein, we characterize the upper respiratory, cloaca, and skin microbiota of loggerhead sea turtles under rehabilitation at the Israeli Sea Turtle Rescue Center located in Mikhmoret, Israel, and the Stazione Zoologica Anton Dohrn located in Napoli, Italy to compare sea turtles’ microbiota in the Eastern Mediterranean Sea (EMS) and the Western Mediterranean Sea. Furthermore, we characterize the breath, skin, and cloaca microbiota of green sea turtles kept in captivity for conservation purposes at the Israeli Sea Turtle Rescue Center. Our results showed significant composition differences between the three groups of sea turtles, their surrounding water, and between the organs assessed within and between species. Additionally, we identified core bacterial taxa for the organs sampled in each sea turtle group. The dominant bacteria in all turtle groups belonged to the Gammaproteobacteria, Bacteroidia and Alphaproteobacteriaclasses. Our study is the first one to enable the comparison of the microbial composition of two loggerhead populations in the Eastern and Western Mediterranean. The results aligned with previous findings regarding the dominant bacterial groups and constituted baseline data for the core microbial communities’ composition on wild chelonians as sentinel species in the Tyrrhenian and Levantine basins. The differences in the bacterial profile enable the identification of the turtles' species, sex, and environment. Changes in the microbiota can also indicate their health status. Additionally, the microbiome characterization of the Israeli green sea turtle population allows the understanding of the microbial community composition of a breeding stock aimed to repopulate the EMS to improve its conservation status practically extinct in the area.