engleski

Microbiota of marine reptiles: it is about more than just the gastrointestinal tract

Loggerhead sea turtles are vastly understudied when it comes to their microbes even though they are considered a keystone species and a potential sentinel species in the Mediterranean Sea. The gastrointestinal (GI) tract bacterial communities are being increasingly explored ; however, loggerheads carry a myriad of unexplored prokaryotic and eukaryotic microorganisms on their shells and skin as well. As bacteria and diatoms are among the first colonizers of underwater surfaces, they also colonize the skin and carapace of sea turtles, establishing complex multi-domain biofilms. Here we describe our efforts in unfolding the bacterial communities associated with the loggerhead sea turtles on several levels: the GI endomicrobiota (oral and cloacal), animal’s surfaces epimicrobiota (skin and carapace), and the turtle-associated diatoms’ phycosphere (bacteria closely associated with diatoms derived from turtles). We obtained oral and cloacal swabs, and skin and carapace scrapings for profiling of the total bacterial community. Skin and carapace scrapings resuspended in sterile seawater were also obtained for isolation of diatoms. Total DNA was extracted from cloacal, oral, carapace, skin, and diatom cultures samples. Bacterial communities were profiled by sequencing V3-V4 (endomicrobiota) and V4 region (epimicrobiota) of the 16S rRNA gene on the Illumina MiSeq platform. Also, bacteria were isolated and cultured from several diatom cultures and identified by partial 16S rRNA gene sequencing. Our results show that the oral microbiota is reflective of the turtle’s environment but that it also maintains several microbial taxa regardless of the environmental shifts. On the other hand, cloacal communities resist change and show a high prevalence of the novel Kiritimatiellaeota phylum and unclassified Proteobacteria, indicating a high incidence of undiscovered bacteria in the marine reptile endomicrobiota. Epimicrobiota is rich in Proteobacteria, Bacteroidota, and Bdellovibrionota phyla, while the associated diatom cultures retain a small portion of specific bacterial taxa in their phycosphere. Also, several bacterial families were enriched in diatom cultures but are rare in source samples (Alcanivoracaceae, Marinobacteraceae, Phycisphaeraceae). Our multi-level investigations provide the first inventory of loggerhead sea turtles’ endo- and epimicrobiota, while revealing high microbial diversity and potential of microbes beyond the gut.

phycosphere, diatoms, microbiota, loggerhead sea turtles

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