The crude control oil has over gut microbiomes

 PAHs (polycyclic aromatic hydrocarbons) are components of crude oil which are released into the marine environment from anthropogenic contamination. These have strong cardiotoxicity effects in fish and can induce immunosuppression. 

Walter et al. (2019) used high-throughput illumine sequencing of the 16s rRNA V4 region to look at the gut microbiome of Gadus morhua (Atlantic cod) from two different locations along Norway: the south where, due to high levels of anthropogenic activities there is expected to be greater amounts of PAHs and from the northern waters which should be pristine in comparison. The bacterial taxa present can be used as a novel indicator of PAH contamination as pollutants are a controlling factor that shapes the gastrointestinal microbiome. 

Several groups of PAH-degrading bacteria were found only in the fish from the southern region including Deferribacteraceae a family which are biomarkers of oil pollution along with many OTUs that represent additional hydrocarbon-degrading bacteria. Comparison of the gut microbiomes suggests that cod from the southern region have a higher exposure to PAHs and therefore require an altered microbiome to breakdown these pollutants. The importance of looking at the functional aspect of the microbiome is highlighted in this paper as the change in pollutants has direct control of the microbiome and the fishes' ability to adapt to the pollutants they encounter. 

Walter, J. M., Bagi, A., & Pampanin, D. M. (2019). Insights into the Potential of the Atlantic Cod Gut Microbiome as Biomarker of Oil Contamination in the Marine Environment. Microorganisms, 7(7), 209.