Epizoic diatoms

Besides investigating microbial communities of Adriatic loggerheads I also investigated the diatom components of those communities. Diatoms are microalgae with silica shells, omnipresent in aquatic environments and crucial for oxygenproduction and CO₂ sequestration on Earth. Interestingly, some of them inhabit only sea turtles (as far as we know). Today we also know diatoms interact with bacteria, sometimes in positive ways and sometimes not so much. Within TurtleBIOME I had the unique opportunity to look into both epizoic diatoms and their bacteria.

From carapace and skin samples of turtles (collected by gentle brushing) I isolated numerous diatom cells and established protocols for their growth in monocultures. We found a myriad of potential new diatom taxa, some of which were described recently in Majewska et al. (2020). Some of the epizoic diatoms I successfully isolated and cultures were analyzed as a part of a much larger dataset to get insight into the evolution of diatoms and their hosts by Ashworth, Majewska et al. (2021). We discovered that some diatom species are faithful to their host while other turtle diatoms were not as faithful and could be found across different host populations.

I also took the opportunity to examine and isolate bacteria associated with my diatoms in culture. Since those diatoms were carefully washed several times before establishing them in culture, we anticipated only bacteria close to the diatom could get transferred as well. Indeed, diatoms had much lower richness of bacteria in culture compared to their source environments (loggerhead carapace and skin). Additionally, we discovered that bacteria that are rare on the surface of the turtles loved growing with diatoms. Also some of them are new to us, so similarly to many novel diatom taxa, we think our turtle host is carrying many novel bacterial taxa as well. These findings are a part of the Filek et al. (2021) publication.

Currently, I am analyzing the data collected from diatom co-culturing experiment. I cultivated Achnanthes elongata (a turtle-associated diatom) together with diatoms considered to be opportunistic and not specific to turtles. The co-cultures were grown for three weeks and imaged every other day by a multi-mode plate reader (16 images per well, 3x wells per condition). From the images, I extracted information on the number of diatoms and their size and orientation (horizontal or vertical). From there I hope to get some ideas on diatom behavior that could tell us more about the epizoic diatom lifestyle preferences. This work is planned to be public in 2024.