A pure strain of Azotobacter vinelandii was isolated from soil samples with no known history of contamination by crude oil, mercury, silver or any other heavy metal salts. The isolate was grown to a density of 10 8 cells/ml as the primary culture, in an enriched mineral Azotobacter medium. From this, 90 ml was pipetted into each of 15 conical flasks divided into five sets of three replicates. A set was treated with mercury (II) chloride (2.5 mmol/l), silver chloride (4.6 mmol/l), Bonny light crude oil (1.0%, w/v), or Fenton reagent. A set with normal Azotobacter medium served as the control. The mean total cell protein harvested from the various flasks ranged from 0.503 to0.245 mg/ml within 48 hr of incubation. The differences in the mean total protein concentrations were statistically significant (p < .05). The protein carbonyl contents from the flasks also were significantly different but for the pair of control/Hg2+ -treated media. Lipid peroxidation levels in all the treated media were significantly higher than that of control. Lipid peroxidation and protein oxidation products signaled cell injury or damage, which might comprom ise cell growth/proliferation and biological nitrogen-fixing activity of the micro-organism in the soil.
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Ikechukwu N.E. Onwurah (1999) studied this question.