Mytilus galloprovincialis as sentinel to detect marine hydrocarbon contamination: an integrated approach

Oil spills cause significant impacts on the coastal marine ecosystem. Studying and investigating the immune mechanisms that contribute in hydrocarbon (HC) detoxification processes is crucial to better understand the responses of marine organisms under pollutant exposure. The mussel Mytilus galloprovincialis, due to its filtration behaviour and the evidence about its ability to response early to environmental stressors, is considered an excellent model species for ecotoxicological studies. In this work, specimens of M. galloprovincialis were exposed for 4 days to different concentrations of dieselengine oil mixture. Increasing concentrations of the mixture significantly decreased the phagocytic activity of the haemocytes. Enzymatic analyses of the main oxidative stress and inflammation markers confirmed the immunomodulation resulting from short-term exposure to the mixture. Histomorphological analyses on digestive gland showed that HCs mixture compromised the tubules’s tissue structures, inducing necrosis especially for the highest concentrations. Furthermore, the modulation of the molecular markers HSP70 and HSC70 was also assessed by western blot, demonstrating their involvement in maintaining the organism's homeostasis. Finally, the effects of HCs mixture on the diversity and structure of microbiome of hepatopancreas and haemolymph were also evaluated by Automated Ribosomal Intergenic Spacer (ARISA) and 16S rRNA gene sequencing analyses. The exposure to increasing HCs concentrations has a positive effect on microbial diversity, with an increase in relative abundance of several known degrading bacterial genera. These results confirmed the role of M. galloprovincialis as a sentinel of environmental pollution, thanks to its ability to respond sensitively and quickly to hydrocarbon pollution.