The microbial diversity and functioning around oceanic islands is poorly described, despite its importance for ecosystem homeostasis. Here, we aimed to verify the occurrence of microbe-driven phenanthrene co-oxidation in the seawater surrounding the Trindade Island (Brazil). We also used Next-Generation Sequencing to evaluate the effects of aliphatic and polycyclic aromatic hydrocarbons (PAHs) on these microbial community assemblies. Microcosms containing seawater from the island enriched with either labelled (9-14C) or non-labelled phenanthrene together with hexadecane, weathered oil, fluoranthene or pyrene, and combinations of these compounds were incubated. Biodegradation of phenanthrene-9-14C was negatively affected in the presence of weathered oil and PAHs but increased in the presence of hexadecane. PAH contamination caused shifts in the seawater microbial community-from a highly diverse one dominated by Alphaproteobacteria to less diverse communities dominated by Gammaproteobacteria. Furthermore, the combination of PAHs exerted a compounded negative influence on the microbial community, reducing its diversity and thus functional capacity of the ecosystem. These results advance our understanding of bacterial community dynamics in response to contrasting qualities of hydrocarbon contamination. This understanding is fundamental in the application and monitoring of bioremediation strategies if accidents involving oil spillages occur near Trindade Island and similar ecosystems.

Centro para Pesquisa Interdisciplinar em Biotecnologia CIP Biotec Universidade Federal do Pampa São Gabriel Rio Grande do Sul Brazil

Department of Sustainable Soils and Grassland Systems Rothamsted Research Harpenden Hertfordshire UK

Laboratório de Biofísica Ambiental Departamento de Biologia Universidade Federal de Viçosa Viçosa Minas Gerais Brazil

Laboratório de Biotecnologia e Biodiversidade para o Meio Ambiente Departamento de Microbiologia Universidade Federal de Viçosa Viçosa Minas Gerais Brazil

Laboratório de Ecologia e Biologia Molecular de Microrganismos Departamento de Biologia Universidade Federal de Juiz de Fora Juiz de Fora Minas Gerais Brazil

Laboratory of Environmental Microbiology Institute of Microbiology of the Czech Institute of Sciences Prague Czech Republic

Soil Microbiology Laboratory Department of Soil Science Luiz de Queiroz College of Agriculture ESALQ USP Piracicaba São Paulo Brazil

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