engleski

From Sea Turtle Associated Microbial Biofilms to Diatom Monocultures: A Bacterial Perspective

Background: Diatoms and bacteria are among the first colonizers of surfaces of submerged non- living objects but are also known to colonize the skin of aquatic animals such as the sea turtles. Sea turtles' carapace and skin harbor putative specific as well as non-specific diatom taxa in association with diverse microbial communities. An increasing number of studies point to the importance of bacteria interacting with planktonic and benthic diatoms but to date little is known about bacterial communities associated with epizoic diatoms. Objectives: This study aims to provide an inventory of diatom-associated bacteria inhabiting the carapace and skin of the loggerhead sea turtle. Methods: We sampled carapaces and skins of loggerhead sea turtles from the Adriatic Sea both for diatom isolation and 16S rRNA gene profiling of the total surface bacterial community. Single diatom cells were isolated and 19 xenic monocultures were established and grown in F2 medium at 18-20 °C in 12:12 h light-dark cycles (7-10 μmol/m2/s) for at least six months prior to bacterial community analyses. Total DNA was extracted from diatom cultures as well as from four carapace samples and two skin samples. The V4 region of the 16S rRNA gene (515F-806R primers) was sequenced via Illumina MiSeq platform. In addition, we isolated bacterial strains from several diatom monocultures and performed initial bacterial strain identification by partial 16S rRNA gene sequencing (BLK1 primer). Results: Preliminary analyses show that bacterial families Rhodobacteriaceae, Flavobacteriaceae, Spongiibacteraceae, Moraxellaceae, and Alteromonadaceae were detected both in the microbiome of skin and carapace samples as well as in diatom cultures, with relative abundances in skin and carapace samples ranging from 1% to 26%. Out of all bacterial isolates (total 117) from ten diatom cultures, 7%, 11%, and 22% of isolates belonged to Flavobacteriaceae, Alteromonadaceae, and Rhodobacteriaceae, respectively. Additionally, groups such as Stappiaceae, Marinobacteriaceae, Thalassospiraceae, and Alcanivoracaceae were detected in carapace and skin microbiomes at relative abundances lower than 1% even though Marinobacteriaceae and Alcanivoracaceae were common constituents of the cultivable portion of the diatom cultures’ bacterial communities (13% and 36% of all bacterial isolates, respectively).

diatoms ; microbiota ; sea turtle ; microbial communities

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