Mercury Influences Uptake of Amino Acids by Marine Bacteria

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Abstract
Natural multispecies bacterial communities, in a resting state and at low initial densities, were used to study effects of dissolved Hg on nutrient absorption. Nutrients were offered as 10 .mu.M amino-acid mixture, in the relative proportions encountered in natural sea-water samples. Uptake, commencing after an initial stationary phase, resulted from induction of transport mechanisms in a relatively constant number of bacteria, rather than from increased densities due to multiplication following nutrient availability. The periods elapsed to reduce ambient amino-acid concentrations to half of the initially present levels were influenced by the presence of low levels of Hg, revealing significant uptake inhibition at a sensitivity threshold of 0.625 .mu.g/l Hg. Low Hg levels affected induction and uptake in dormant bacteria but had no effect on uptake in a high density community in the log phase. Higher levels of up to 488 .mu.g/l Hg decreased rates of uptake and prolonged the duration of lag phases, due to changes in species composition. Use of natural multispecies communities allowed the simultaneous quantitative detection of a sequence of different Hg levels, varying from lowest (0.625) to highest (488 .mu.g/l Hg) ambient concentrations. Initially present levels of total (2.5 .mu.g/l) and dissolved Hg decreased rapidly, while Hg associated with the particulate material increased to constant values between 12-16 h after the start of experiments. Toxicity was due less to concentration of Hg alone than to the relation between concentration and biomass. Because of unavoidable changes in sea-water properties resulting from handling between sampling and start of the tests (transport, storage and freeing of collected samples from originally present bacteria), the procedure is probably not appropriate for detecting subtle differences in water quality present in the sea at dumping sites and in adjacent polluted areas.

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