Heavy metal tolerance in chromogenic and non-chromogenic marine bacteria from Arabian Gulf

A simple method - direct agar diffusion assay - was optimised for rapid assessment of heavy metal toxicity to marine chromogenic and non-chromogenic bacteria. The procedure involved spotting of a 10 microliter test solution on the seeded agar plate and incubation of the plates at 30 degrees C to accelerate bacterial growth. Under optimum conditions, test results were obtainable within 12-18 hr instead of 96 hr incubation time generally required for a marine bacterial assay by conventional agar plate methods. A range of sixteen heavy metals, each at 5 different concentrations was tested. Toxicity was demonstrated by the formation of a clear zone of growth inhibition around the point of application. Toxicity of tested chemicals could be easily demonstrated at concentrations as low as 0.1 mu g per spot on the agar plate. A dose dependent relation between metal concentration (mu g/spot) and the diameter of the clear zone on agar plate was observed, suggesting potential of this method as an easy and economical tool in quantitative toxicology studies.