PATTERN OF COTOLERANCE IN MARINE PERIPHYTON COMMUNITIES ESTABLISHED UNDER ARSENATE STRESS

Arsenate-tolerant marine periphyton communities established under arsenate stress in a flow-through aquarium system, were investigated for cotolerance to various inhibitors of photosynthesis. A short-term test system for inhibition of periphyton photosynthesis was used to quantify the community tolerance levels. Preexposure to arsenate at 10-mu-M increased arsenate tolerance > 16,000-fold compared to control communities established at background levels of arsenate. A substantial cotolerance was observed only for thiophosphate which is a phosphate analog uncoupler of photophosphorylation with a mode of action similar to that of arsenate. For the uncouplers CCCP (carbonyl cyanide m-chloro-phenylhydrazone) and Primene JMT (a primary amine with a branched C18-C22 aliphatic chain), the inhibitor of photosynthetic electron transport DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and arsenite, there was a general tendency for a small cotolerance, although for Primene JMT and DCMU an increased sensitivity was sometimes observed. The general increase in tolerance was however quantitatively insignificant compared to the specific cotolerance observed for thiophosphate, suggesting that the mode of action and tolerance mechanisms are similar for arsenate and thiophosphate, and most likely related to their phosphate analogy. We suggest that significant cotolerance is not ubiquitous nor common in periphyton, and that the emerging cotolerance pattern may be indicative of the toxicity and tolerance mechanisms.