Participation of Reactive Oxygen Intermediates in the Killing of Ingested Bacteria by Crassostrea gigas Hemocytes

Abstract

The participation of reactive oxygen intermediates (ROIs) in the killing of ingested bac -teria by hemocytes of the Pacific oyster, Crassostrea gigas, has been investigated under aerobic and anaerobic conditions. In the present study, we used five different species as target organisms, i.e., Arthrobacter ramosus, Bacillus subtilis, Deleya pacifica, Escherichia coli, and Micrococcus luteus . In order to measure the ROI-production by the C. gigas hemocytes, we used chemiluminescence (CL). Significant stimulation of the hemocyte-derived CL occurred in response to A. ramosus , whereas no increase in the ROI-generation was observed when the C. gigas hemocytes were exposed to the other four bacterial species. Although the C. gigas hemocytes exerted a phagocytic ability against all the bacterial strains tested, there were no statistical differences in all the bacterial strains under both aerobic and anaerobic conditions. In the anaerobic environment, the intracellular killing per -cent of A. ramosus by the C. gigas hemocytes significantly decreased to 36.7% when compared with the 66.2% intracellular killing under the aerobic conditions. Contrary to the intracellular killing activity of the C, gigas hemocytes toward the other four bacterial strains, there was no significant difference between the aerobic and anaerobic environments. Intracellular killing of A. ramosus was also repressed by the addition of diphenyleneiodonium (DPI), which is a potent inhibitor of NADPH oxidase.