Effect of Azamethiphos on enzymatic activity and metabolic fingerprints of marine microbial communities from the water column

Salmon production in Chile has increased significantly since the 1990s. However, there have been significant economic losses owing to outbreaks of Caligus rogercresseyi. Pesticides, among them Azamethiphos, are used to mitigate the impact of this sea louse. Azamethiphos can affect non-target species living near salmon farms such as microbial plankton, although there is little information about this. The general objective of this study was to determine the effect of different concentrations of the pesticide Azamethiphos on the metabolism of microbial plankton communities (< 100 mu m) in two contrasting zones, one without salmon farming and the other with a high level of aquaculture activity. Several methodological approaches were used, including the enzymatic activity of j3-glucosidase and malate dehydrogenase (MDH), fingerprinting techniques (EcoPlates for bacteria and FF microplate for marine fungi) and the estimation of microbial aerobic respiration. We found greater de gradation of the pesticide Azamethiphos in the salmon culture zone (-72.4%) than in an area not previously used in salmon production (-26.1%). The response of microbial beta-glucosidase activity to Azamethiphos is highly variable, but there is a tendency toward more activity in the smaller size fractions (5-25 mu m and 0.22-3 mu m) when exposed to high Azamethiphos concentrations. We also detected a highly variable response in microbial MDH activity. The most widely used carbon substrates by bacterioplankton and marine fungi are those related to carbohydrate metabolism. We also found increased use of carboxylic acids and amino acids in the treatments with higher concentrations of Azamethiphos. Enzyme activity, together with metabolic fingerprints, could be used as an indicator of perturbations in marine microbial communities.