504
in water and sediment (Hazen et al. 2010; Kostka et al. 2011; Mason et al. 2014),
but only a handful of papers have examined this effect on marine fish species. Arias
et al. (2013) and Larsen et al. (2015) examined the effects of oil exposure on the
skin microbiome of the Gulf killifish and found no evidence for a linkage between
oil exposure and skin microbiome shifts using culture-based approaches and ribosomal intergenic spacer analysis (RISA), although neither paper reported concentrations of PAHs in water or sediment where the samples were collected. In
contrast, both Brown-Peterson et al. (2015) and Bayha et al. (2017) showed that
laboratory exposure to oil-contaminated sediment (54 and 57 mg/kg ∑50PAH,
respectively) altered the microbiome of both gills and intestines in southern flounder in ways that were clearly associated with the oil exposure, including a significant increase in the prevalence of bacteria linked to hydrocarbon degradation in
upper gill, lower gill, and intestinal communities. Both studies used predictive
metagenomics to show that KEGG (Kyoto Encyclopedia of Genes and Genomes)
pathways involved in contaminant degradation increased in abundance following
oil exposure and pathways involved in biosynthesis of metabolically important
compounds were strongly decreased in abundance following exposure to oil-contaminated sediments.
The effect of oil exposure on the commensal microbiome is likely worthy of
further study as there is a clearly demonstrated linkage between intestinal Ahr
receptor ligands and the intestinal microbiome in vertebrates. In particular, Ahr activation has been demonstrated to play a strong role in mediating tetrachlorodibenzofuran contaminant-driven shifts in intestinal microbiome structure in mice (Zhang
et al. 2018). The idea that expression of certain proteins affected by oil exposure
(such as Ahr) could influence the structure of the host microbiome has interesting
consequences for studying the interaction of host and contaminants.
29.3.6 Impacts on Immune Function
The immune system of fish, like that of mammals, is comprised of innate and adaptive immunity. Innate immunity is considered the first line of defense through
physical barriers and nonspecific recognition of microbial molecular patterns,
whereas adaptive immunity, the second line of defense, is comprised of humoral
and cell- mediated immunity, in which specific antigen recognition leads to either
B cell proliferation and antibody production or cytotoxic T cell proliferation. Both
the innate and adaptive immune responses use a complex network of signaling
molecules (cytokines, chemokines), specialized cells, and organs that work in concert to clear microbial pathogens and maintain immunological homeostasis (Rauta
et al. 2012).
Oil exposure can have a direct effect on the immune system through biotransformation or detoxification systems such as the cytochrome P450 (CYP) enzyme system. These systems are shown to be interrelated and not exclusively independent. In
M. Grosell et al.
in water and sediment (Hazen et al. 2010; Kostka et al. 2011; Mason et al. 2014),
but only a handful of papers have examined this effect on marine fish species. Arias
et al. (2013) and Larsen et al. (2015) examined the effects of oil exposure on the
skin microbiome of the Gulf killifish and found no evidence for a linkage between
oil exposure and skin microbiome shifts using culture-based approaches and ribosomal intergenic spacer analysis (RISA), although neither paper reported concentrations of PAHs in water or sediment where the samples were collected. In
contrast, both Brown-Peterson et al. (2015) and Bayha et al. (2017) showed that
laboratory exposure to oil-contaminated sediment (54 and 57 mg/kg ∑50PAH,
respectively) altered the microbiome of both gills and intestines in southern flounder in ways that were clearly associated with the oil exposure, including a significant increase in the prevalence of bacteria linked to hydrocarbon degradation in
upper gill, lower gill, and intestinal communities. Both studies used predictive
metagenomics to show that KEGG (Kyoto Encyclopedia of Genes and Genomes)
pathways involved in contaminant degradation increased in abundance following
oil exposure and pathways involved in biosynthesis of metabolically important
compounds were strongly decreased in abundance following exposure to oil-contaminated sediments.
The effect of oil exposure on the commensal microbiome is likely worthy of
further study as there is a clearly demonstrated linkage between intestinal Ahr
receptor ligands and the intestinal microbiome in vertebrates. In particular, Ahr activation has been demonstrated to play a strong role in mediating tetrachlorodibenzofuran contaminant-driven shifts in intestinal microbiome structure in mice (Zhang
et al. 2018). The idea that expression of certain proteins affected by oil exposure
(such as Ahr) could influence the structure of the host microbiome has interesting
consequences for studying the interaction of host and contaminants.
29.3.6 Impacts on Immune Function
The immune system of fish, like that of mammals, is comprised of innate and adaptive immunity. Innate immunity is considered the first line of defense through
physical barriers and nonspecific recognition of microbial molecular patterns,
whereas adaptive immunity, the second line of defense, is comprised of humoral
and cell- mediated immunity, in which specific antigen recognition leads to either
B cell proliferation and antibody production or cytotoxic T cell proliferation. Both
the innate and adaptive immune responses use a complex network of signaling
molecules (cytokines, chemokines), specialized cells, and organs that work in concert to clear microbial pathogens and maintain immunological homeostasis (Rauta
et al. 2012).
Oil exposure can have a direct effect on the immune system through biotransformation or detoxification systems such as the cytochrome P450 (CYP) enzyme system. These systems are shown to be interrelated and not exclusively independent. In
M. Grosell et al.