Community Structure of Skin Microbiome of Gulf Killifish, Fundulus grandis, Is Driven by Seasonality and Not Exposure to Oiled Sediments in a Louisiana Salt Marsh

Mucus of fish skin harbors complex bacterial com- munities that likely contribute to fish homeostasis. When the equilibrium between the host and its external bacterial symbi- onts is disrupted, bacterial diversity decreases while opportu- nistic pathogen prevalence increases, making the onset of path- ogenic bacterial infection more likely. Because of that relation- ship, documenting temporal and spatial microbial community changes may be predictive of fish health status. The 2010 Deepwater Horizon oil spill was a potential stressor to the Gulf of Mexico's coastal ecosystem. Ribosomal intergenic spacer analysis (RISA) and pyrosequencing were used to ana- lyze the bacterial communities (microbiome) associated with the skin and mucus of Gulf killifish (Fundulus grandis )t hat were collected from oiled and non-oiled salt marsh sites in Barataria Bay, LA. Water samples and fin clips were collected to examine microbiome structure. The microbiome of Gulf killifish was significantly different from that of the surrounding water, mainly attributable to shifts in abundances of Cyanobacteria and Proteobacteria. The Gulf killifish's microbiome was dominated by Gammaproteobacteria, specifi- cally members of Pseudomonas. No significant difference was found between microbiomes of fish collected from oiled and non-oiled sites suggesting little impact of oil contamination on fish bacterial assemblages. Conversely, seasonality significant- ly influenced microbiome structure. Overall, the high similarity observed between the microbiomes of individual fish observed during this study posits that skin and mucus of Gulf killifish have a resilient core microbiome.