Naz, Naghma (2003) GENETICS OF METAL PRECIPITATION BY FRESH WATER AND MARINE SULPHATE REDUCING BACTERIA (SRB). PhD thesis, University of Karachi, Karachi.
Toxic metals and organic compounds are known hazards for biological ecosystems with both kinds of pollutant often being present together in contaminated wastes. Sulphate-reducing bacteria (SRB) may play an important role in anaerobic bioremediation of both organic and inorganic pollutants. In this study, SRB strains showed tolerance (up to 5 mM) towards phenol, benzoic acid and catechol. The strains also grew in the presence of cadmium, however variations were observed with respect to cadmium toxicity between the cultures as revealed by their patterns of lactate utilization, acetate production, sulphate-reduction and protein production. Desulfovibrio vulgaris DSM 644 showed the least tolerance while Desulfovibrio desulfuricans DSM 1926 and Desulfococcus multivorans DSM 2059 showed maximum tolerance towards cadmium. Treatments with cadmium in combination of either phenol, benzoic acid or catechol showed no significant effect on growth compared to growth on cadmium alone for three SRB strains tested. However, a mixed SRB culture showed decreased tolerance to cadmium in the presence of phenol, benzoic acid and catechol and Desulfomicrobium norvegicans II showed increased tolerance to cadmium in presence of phenol and benzoic acid. All SRB strains tested were found capable to precipitate cadmium as sulphide from the growth medium. Metal removal was also observed in the presence of the organic compounds but less metal precipitation was detected in the presence of catechol. Two strains, Desulfovibrio vulgaris DSM 644 and Desulfococcus multivorans DSM 2059 showed oxidation of phenol and benzoic acid. Benzoic acid oxidation was also demonstrated by Desulfovibrio desulfuricans DSM 1926. Transmission electron microscopy of Desulfovibrio desulfuricans DSM 1926 and Desulfococcus multivorans DSM 2059 revealed intracellular accumulation of cadmium suggesting the presence of metal transport and defence mechanisms inside the cell This was confirmed by the presence of homologous DNA sequences that code for bacterial metallothioneins in all SRB strains. Desulfovibrio desulfuricans DSM 1926 and Desulfococcus multivorans DSM 2059 also showed DNA homology with known genes encoding heavy metal translocating ATPases. It is concluded that SRB may show considerable potential for the bioremediation of co-polluted habitats.
|Item Type:||Thesis (PhD)|
|Uncontrolled Keywords:||metal precipitation, sulphate reducing bacteria, toxic metals, anaerobic bioremediation, pollutants, cadmium, phenol benzoic acid, catechol|
|Subjects:||Biological & Medical Sciences (c) > Biological Sciences(c1) > Evolution & genetics (c1.6)|
|Deposited By:||Mr. Muhammad Asif|
|Deposited On:||14 Feb 2007|
|Last Modified:||14 Oct 2009 15:24|
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