Abstract
Interactions of living benthic epiphytic foraminifera, Pararotalia spinigera (Le Calvez) and Rosalina macropora (Hofker), with unidentified natural organic compounds (UNOC) derived from decomposed seaweeds, heavy metal ions and three tracer xenobiotics, acridine orange (AO), neutral red (NR) and fluorescein (FLU), were investigated. Changes of redox state of nicotinamide adenine dinucleotide (NAD) in foraminifera, induced by UNOC, indicated that these compounds contained both metabolic substrates and toxic components (natural uncouplers). The presence of toxic components in UNOC was confirmed by results of a dye extrusion test with FLU with cadmium ions acting as an uncoupler. The following defense mechanisms against xenobiotics were discovered in foraminifera studied: (1) mucopolysaccharide coat that forms additive diffusion barriers and binds some cationic xenobiotics, (2) plasma membrane that forms impermeable diffusion barrier against natural and anthropogenic anionic xenobiotics, (3) membrane carrier-mediated transport system for elimination of anionic xenobiotics from the cell, (4) active intralysosomal accumulation and isolation of some cationic xenobiotics, (5) peroxidases that protect foraminiferal cytoplasm against an excess of oxygen and peroxides, (6) haloperoxidases that protect the cytoplasm against Brand I- penetration and produce brominated or iodinated xenobiotics, and (7) metallthioneine-like Cu2+-binding tryptophan-containing proteins protecting the foraminifera against some toxic metals. Presence of UNOC in seawater decreased acute toxicity of heavy metal ions for foraminifera. The state of the defense system against xenobiotics in benthic epiphytic foraminifera can serve as a very sensitive biomarker for monitoring and prediction of ecological consequences of anthropogenic pollution.
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