Nweke et al.:Toxicity of zinc to heterotrophic bacteria froma tropical river sediment APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 5(1): 123-132 Abstract. Tolerance to Zn 2+ by pure cultures of Bacillus, Salmonella and Arthrobacter species isolated from New Calabar River sediment was assessed through dehydrogenase assay. The cultures were exposed to Zn 2+ concentrations of 0.2 to 2.0 mM in a nutrient broth-glucose-TTC medium. The responses of the bacterial strains varied with Zn 2+ concentration.

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... In Salmonella sp. SED2, Zn 2+ stimulated dehydrogenase activity at 0.2 mM. In Bacillus sp. SED1 and Arthrobacter sp. SED4, dehydrogenase activity was progressively inhibited with increasing Zn 2+ concentration. The IC 50 ranges from 0.206 ± 0.030 to 0.807 ± 0.066 mM. Total inhibition of dehydrogenase activity was observed at concentrations ranging from 1.199 ± 0.042 to 1.442 ± 0.062. The order of zinc tolerance is: Salmonella sp. SED2 > Arthrobacter sp. SED4 > Bacillus sp. SED1. The result of the in vitro study indicated that Zinc is potentially toxic to sediment bacteria and could pose serious threat to their metabolism in natural environments.