Combination of a pesticide exposure and a bacterial challenge: In vivo effects on immune response of Pacific oyster, Crassostrea gigas (Thunberg)

Abstract

To assess the impact of pollution induced by pesticides on Pacific oyster, Crassostrea gigas, health in France, in vivo effects of combined pesticide exposure and bacterial challenge on cell activities and gene expression in hemocytes were tested using flow cytometry and real-time PCR. As a first step, an in vivo model of experimental contamination was developed. Pacific oysters were exposed to a mixture of eight pesticides (atrazine, glyphosate, alachlor, metolachlor, fosetyl-alumimium, terbuthylazine, diuron and carbaryl) at environmentally relevant concentrations over a 7-day period. Hemocyte parameters (cell mortality, enzyme activities and phagocytosis) were monitored using flow cytometry and gene expression was evaluated by real-time PCR (RT-PCR). The expression of 19 genes involved in C. gigas hemocyte functions was characterized using RT-PCR. After 7 days of exposure, phagocytosis was significantly reduced and the 19 selected genes were down-regulated in treated animals. As a second step, the experimental contamination method previously developed was used to study interactions between pesticide exposure and bacterial challenge by intramuscular injection of two Vibrio splendidus-related pathogenic strains. Oyster mortality and expression of 10 of the 19 selected genes were followed 4 and 24h post-injection. Oyster mortality was higher in pesticide-treated oysters compared to untreated oysters after the bacterial challenge. Gene expression was up-regulated in pesticide-treated oysters compared to untreated oysters after the bacterial challenge. We hypothesize that gene over-expression due to an interaction between pesticides and bacteria could lead to an injury of host tissues, resulting in higher mortality rates. In conclusion, this study is the first to show effects of pesticides at environmentally relevant concentrations on C. gigas hemocytes and to hypothesize that pesticides modulate the immune response to a bacterial challenge in oysters.

Effects of Pesticides on Marine Bivalves: What Do We Know and What Do We Need to Know?

“…A study with a mix of herbicides containing atrazine, diuron and isoproturon revealed effects on gene expression in the Pacific cupped oyster, Crassostrea gigas (Tanguy et al, 2005). Gagnaire et al (2007) studied also the impact of pesticides on C. gigas, monitoring gene expression in hemocytes by real-time PCR. The expression of genes involved in C. gigas hemocyte functions was up-regulated in pesticide-treated oysters compared to untreated oysters after a bacterial challenge.…”

“…It has been shown in several vertebrates and invertebrates that pesticides are capable of diminishing immune defenses and/or of modifying genomes. They may render animals more vulnerable to infectious diseases (Ross et al, 1996;Gagnaire et al, 2007). Although pesticide effects on marine bivalves have been already studied in bivalves, a few of reviews summarizing their different effects are available.…”

Variability of fresh- and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment

“…The intensive irrigation and the use of pesticides provoked a deterioration of the water quality and quantity used to refill oyster ponds. This deterioration had strong impact on the oyster maturing (Gagnaire et al, 2007(Gagnaire et al, , 2006.…”

The Effects of 4-Nonylphenol on the Immune Response of The Pacific Oyster, Crassostrea Gigas, Following Bacterial Infection (Vibrio Campbellii)

“…These results suggest that exposure to noylphenol at high enough levels has the ability to modulate Cg-galectin gene expression. In their study examining effects of pesticides on oyster immunity, Gagnaire et al (2007) suggested that pesticides modified the oyster immune response by inducing an up-regulation of genes involved in hemocyte functions and defense mechanisms as we see here. Despite this up-regulation, they saw higher mortality in bacterially treated oysters.…”

“…Subsequent to exposure, oysters mount two-fold defense mechanisms encompassed by cellular and humoral components that work in concert to recognize and eliminate pathogens. Despite lack of an acquired immunity that relies on immunological memory (i.e., antibodies), C. gigas has a developed system that can discriminate advantageous microorganisms from deleterious ones (Canesi et al, 2002;Gagnaire et al, 2007).…”