Determination of Heavy Metals Tolerance and their Damaging Effects on a Local Soil Thermophilic Isolate Bacillus stearothermophilus

Abstract

This research aimed to detect the tolerance of a local soil thermophilic isolate to some heavy metals (HM) and determine of minimal inhibition concentration (MIC). Also, plasmid profile was studied and its relationship with HM resistant. Deleterious effect of mercury (Hg), chromium (Cr) and Cobalt (Co) were evaluated on bacterial shape, growth and DNA scan between 200-40nm. Mutation effect was also studied. Local thermophilic Bacillus stearothermophilus was resist zinc, molbidium, silver at a concentration reached 80mM; it is sensitive to Hg, Cr and Co with MIC reached 0.004, 0.03 and 0.007 respectively. Plasmid profile revealed the absence of plasmid from B. stearothermophilus. Some of bacterial shapes were changed to short bacilli, coccobacilli and cocci; many bacterial cell fragment were seen after treatment with Hg, Cr and Co. Bacterial growth decreased when treated with Hg and Cr after 18h while, little effect was seen with Co treatment with Hg and Co induced heat sensitive mutation with 200-300 mutated cfu /ml from 10⁴ cfu/ml; no heat sensitive mutation were detected for Cr treatment. DNA UV scan 200-400nm showed no changes with Hg while, curve shape changed for Cr and cobalt.