Pakistan Research Repository


Talat, Mah-e- (2000) GENETIC MECHANISM OF HEAVY METAL RESISTANCE OF PSEUDOMONAS AERUGINOSA CMG103. PhD thesis, University of Karachi, Karachi.



Eight bacterial strains, designated as strains CMG101-CMG108, were isolated from metal polluted water samples of the Malir river, Karachi, Pakistan, for their resistance to high concentrations of Zn. Although all strains were identified as Pseudomonas aeruginosa species, they were considered as different strains on the basis of various characteristics. Beside Zn, the CMG strains displayed significant resistance to Cd and some tolerance to Bi and Te. The comparative study of CMG isolates with other known reference strains showed that CMG103 and CMG108 exhibited one of the highest resistance against Zn and Cd reported i.e., up to 8 mM Zn and 2mM Cd Growth experiments at high temperature and induction experiments indicate that the resistance for Zn and Cd in P.aeruginosa strains CMG103 and CMG108 is linked and controlled by an active metal resistance system. Since both, CMG103 and CMG 108, did not show the presence of plasmids, it was assumed that Zn/Cd resistance is mediated by a chromosomal borne locus. A mutant, czr-13km CMG108#13, impaired in Zn/Cd resistance was obtained in CMG108 by km transposon mutagenesis. Czr-13km was found to be complemented by a genomic 12.8 kb HindIII fragment of CMG103 cloned in pLAFR3. DNA-DNA hybridization studies revealed the presence of czr in a conserved region of P.aeruginosa from different origins Nucleotide sequence of this fragment demonstrated the presence of four potential genes czrRCBA covering about approximately 6598 bp involved in Zn and Cd resistance and two ORFs which showed similarities with aromatic catabolic genes. The comparison of czrCBA with other sequences in the Genbank EMBL data base demonstrated significant similarities with the structural genes of the plasmid brone metal resistant determinants czr, ncc and cnr. The remarkable similarities with ZcrCBA/CNRCBA which determine a cation-antiporter efflux system suggest that a similar kind of efflux system functions in P.aeruginosa. The predicted protein sequence of the potential regulatory gene, czrR, showed significant similarities cop and pco of P. syringae pv. Tomatoe and E. coli, respwctrively, czrR is located upstream of czrCBA and is divergently described The heterolgous expression of czr was examined in various strains. In P.fluorescens and A. eutrophus, czr was expressed at low level, while there was no expression in E.coli. However, spontaneous mutants showing increased resistance to Zn and Cd were observed in A.eutrophus due to the insertion of DNA sequences originating from the chromosome of A. eutrophus. These insertion were located in the region containing czrR and the proposed promoter of the czrCBA operon. Insertion of the DNA sequences from A. eutrophus chromosomal DNA in the regulatory region of CZR decreased its expression in P.aeruginosa. This selection was found to be useful to fish out mobile genetic elements in A.eutrophus

Item Type:Thesis (PhD)
Uncontrolled Keywords:pseudomonas aeruginosa cmg103, bacterial strains, dna sequences, heavy metal pollution
Subjects:Biological & Medical Sciences (c) > Biological Sciences(c1) > Evolution & genetics (c1.6)
ID Code:1077
Deposited By:Mr. Muhammad Asif
Deposited On:20 Dec 2006
Last Modified:04 Oct 2007 21:04

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