Abstract
BackgroundThe expansion of offshore oil exploration increases the risk of marine species being exposed to oil pollution in currently pristine areas. The adverse effects of oil exposure through toxic properties of polycyclic aromatic hydrocarbons (PAHs) have been well studied in Atlantic cod (Gadus morhua). Nevertheless, the fate of conjugated metabolites in the intestinal tract and their effect on the diversity of intestinal microbial community in fish is less understood. Here, we investigated the intestinal microbial community composition of Atlantic cod after 28 days of exposure to crude oil (concentration range 0.0–0.1 mg/L).ResultsAnalysis of PAH metabolites in bile samples confirmed that uptake and biotransformation of oil compounds occurred as a result of the exposure. Various evidence for altered microbial communities was found in fish exposed to high (0.1 mg/L) and medium (0.05 mg/L) concentrations of oil when compared to fish exposed to low oil concentration (0.01 mg/L) or no oil (control). First, altered banding patterns were observed on denaturing gradient gel electrophoresis for samples pooled from each treatment group. Secondly, based on 16S rRNA sequences, higher levels of oil exposure were associated with a loss of overall diversity of the gut microbial communities. Furthermore, 8 operational taxonomic units (OTUs) were found to have significantly different relative abundances in samples from fishes exposed to high and medium oil concentrations when compared to samples from the control group and low oil concentration. Among these, only one OTU, a Deferribacterales, had increased relative abundance in samples from fish exposed to high oil concentration.ConclusionsThe results presented herein contribute to a better understanding of the effects of oil contamination on the gut microbial community changes in fish and highlight the importance of further studies into the area. Our findings suggest that increased relative abundance of bacteria belonging to the order Deferribacterales may be indicative of exposure to oil at concentrations higher than 0.05 mg/L.
Highlights
The expansion of offshore oil exploration increases the risk of marine species being exposed to oil pollution in currently pristine areas
Support parameters Chemical analysis of the Troll C crude oil used in this exposure confirmed that all 16 Environmental Protection Agency (EPA) polycyclic aromatic hydrocarbon (PAH) were present, their sum was 1.6 g/L
Chemical analysis showed that Troll C crude oil, to other crude oils used in exposure studies of Atlantic cod, e.g., North Sea crude, contained significant amounts of PAHs
Summary
The expansion of offshore oil exploration increases the risk of marine species being exposed to oil pollution in currently pristine areas. The fate of conjugated metabolites in the intestinal tract and their effect on the gut microbiota is still under investigation. Considering the metabolic diversity of the gut microbiota, conjugated metabolites could undergo biotransformation as a result of bacterial activity in the gastrointestinal (GI) tract [11]. Studies on the potential interactions between biliary metabolites and gut microbiota in fish are scarce, and most microbiota studies have so far been carried out on mammals, e.g., mice and humans [13, 14]. Their results indicate that gut microbiota can be actively involved in biotransformation of environmental pollutants. These pollutants can in return influence the composition of the gut microbiota
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