Geosmin and 2-methylisoborneol exposure affects immune-related gene expression in rainbow trout (Oncorhynchus mykiss)

The terpenoid compounds geosmin (GSM) and 2-methylisoborneol (MIB), produced by a wide range of microorganisms, are abundant in many aquatic environments. Both compounds are easily detectable by humans (<5 ng/L), and they are often associated with an earthy and musty unpleasant odor in drinking water and aquatic food products (such as fish and shellfish, blue food), which are costly to circumvent. These compounds are well known to bioaccumulate in larger organisms, such as fish, but the interactions between immune responses and these off-flavor compounds are not well known. We evaluated if prior exposure to these compounds can affect immune gene expression in trout. Juvenile (∼9 g) rainbow trout (Oncorhynchus mykiss) were exposed to geosmin and MIB in environmentally relatable concentrations as well as a high concentration (10, 50, 500, 1000 ng/L) for 24 h before IP injection of lipopolysaccharide (LPS) eliciting inflammatory reactions in trout. Following another 24 h fish were euthanized and liver and spleen were sampled for gene expression measurements (qPCR). Both geosmin and MIB significantly altered expression of several immune-related genes in a tissue- and concentration-dependent manner. Geosmin exposure was associated with a dosage dependent down-regulation in the liver of genes encoding cytokines (IL-4/13a, IL-12, TNFα), acute phase proteins (SAA, precerebellin), antimicrobial peptides (cathelicidin 1 and 2), T cell markers (TCR, CD 8), and B cell marker (IgDm). This may have implications for fish in general, but is particularly notable for those living in eutrophicated waters.