Cytochrome P450 (CYP) proteins are involved in the first line of detoxification mechanism against diverse polycyclic aromatic hydrocarbons (PAHs) including benzo[a]pyrene (B[a]P). In aquatic invertebrates, there is still a lack of knowledge on the CYP genes involved in the molecular response to B[a]P exposure due to limited gene information. In this study, we cloned the entire 25 CYP genes in the monogonont rotifer Brachionus koreanus with the aid of next generation sequencing (NGS) technologies and analyzed their transcript profiles with a real-time RT-PCR array to better understand B[a]P-triggered molecular response over different time courses. As a result, B[a]P exposure induced CYP2/3-involved detoxification mechanisms and defensome, including phase II detoxification and antioxidant systems with a modulation of the chaperone heat shock protein (hsp) expression but did not change expression of other CYP clans in B. koreanus . Therefore, we found that B[a]P induced a strong detoxification mechanism to overcome detrimental effects of B[a]P associated with B[a]P-induced growth retardation as a trade-off in fitness costs. Also, this approach revealed that the entire CYP profiling can be a way of providing a better understanding on the mode of action of B[a]P in B. koreanus with respect to molecular defense metabolism.

To examine the deleterious effects of the water accommodated fraction (WAF) of crude oil, the growth curve, fecundity, and lifespan of the monogonont rotifer (Brachionus koreanus) were measured for 24 h in response to three different doses (0.2×, 0.4×, and 0.8×) of WAFs. A higher dose of WAFs significantly reduced the fecundity and lifespan. A rotifer 32K microarray chip showed that the Bk-CYP3045C1 gene had the highest expression. Of the 25 entire CYP genes, the Bk-CYP3045C1 gene showed a significant expression for different doses and times in response to WAFs and chemical components of WAFs (naphthalene and phenanthrene); also, glutathione S-transferase genes, ABC transporter, and other genes showed dose responses upon exposure to 80% WAF over time. Different doses of WAFs increased the oxidative stress with an induction of reactive oxygen species (ROS) and a depletion of glutathione (GSH). Exposure to WAFs did not show toxic effects on survivability in B. koreanus; however, toxicity to WAFs was shown when piperonyl butoxide, a potent inhibitor of cytochrome P450 (CYP) enzymes, was added. This toxicity was dose-dependent. After WAFs exposure, p-ERK was activated over time in response to WAFs, which suggests that WAFs can be activated by the p-ERK signaling pathway.