Culturing Putatively Obligate Epizoic Diatoms: Insights for the Evolution and Ecology of Diatoms and Their Host

Background: Our understanding of the importance of microbiomes on large aquatic animals—such as whales, sea turtles and manatees—has advanced considerably in recent years. Recent activity describing the epizoic diatoms growing on marine vertebrates suggests that these epibiotic diatom communities constitute diverse, polyphyletic, and compositionally stable assemblages that include both putatively obligate epizoic and generalist species. Here, we outline a successful attempt to culture putatively obligate epizoic diatoms without their hosts and propose further applications and research avenues in this growing area of study. Results: We cultured cells of epizoic diatoms from multiple host species sampled in the wild and captivity. Analyzing the DNA sequences of these cultures, we found that several unique diatom taxa have independently evolved to occupy in epibiotic habitats. We created a library of reference sequence data for use in metabarcoding surveys of sea turtle and manatee microbiomes that will further facilitate the use of environmental DNA for studying host specificity in epizoic diatoms and the utility of diatoms as indicators of host ecology and health. Conclusions: Our discovery that epizoic diatoms can be cultured independently from their hosts raises several questions about the nature of the interaction between these diatom species and their hosts. We encourage the interdisciplinary community working with marine megafauna to consider including diatom sampling and diatom analysis into their routine practices.