Journal article
Biochemical characterization of a multiple heavy metal, pesticides and phenol resistant Pseudomonas fluorescens strain


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Author list: Samina Wasi, Ghulam Jeelani, Masood Ahmad *
Publication year: 2007
Volume number: 71
Issue number: 2008
Start page: 1348
End page: 1355
Number of pages: 8
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Pseudomonas fluorescens SM1 isolate was found to be resistant to some major water pollutants namely Cd2+, Cr6+, Cu2+, Ni2+, Pb2+,
BHC, 2,4-D, mancozeb and phenols up to a concentration four times to the normal levels occurring in the highly pollulated regions.
Curing experiment brought about the loss of one or more resistance markers indicating the plasmid born resistance. Plasmid profile
of SM1 strain showed the presence of one DNA band of 43.6 kb. This Plasmid was isolated from SM1 strain and introduced into Escherichia coli DH5a with a transformation frequency of 6.7 104 transformants/recipient cell. The test SM1 strain was also capable of
biotransforming Cr(VI) to Cr(III) which is less toxic compounds. Present studies further indicated that the test SM1 strain was not only
resistant to 2,4-D, phenols and catechol but also capable of bioremediating these toxicants quite efficiently. Moreover, studies with inhibitors like sodium azide, 2,4-DNP and chloramphenicol suggested that the major mechanism for the bioremediation of the heavy metals
other than Cr6+ would be the biosorption process.
2007 Elsevier Ltd. All rights reserved.
Keywords: Transformation; Curing; Pseudomonas fluorescens; Plasmid; Escherichia coli DH5a; Biosorption
1. Introduction
Pseudomonas fluorescens belongs to a group of common
non-pathogenic saprophytes that colonize soil, water and
plant surface environments. Physiological and genetic
features of Pseudomonas make them a promising agent for
utilization in biotechnology, agriculture and environmental
bioremediation applications. The ability to biodegrade hazardous chemical wastes is an interesting feature of P. fluorescens (Appanna and Hamel, 1996; Barathi and Vasudevan,
2003). Heavy metals, pesticides, as well as phenols all pose
a serious threat to living systems. They can react with proteins, nucleic acids and phospholipids, and thus arrest cellular proliferation (Frausto da Silva and Williams, 1993).
Environmental pollution by heavy metals as a result of
fossil fuel burning and industrial discharges has been
increasing. In the case of water bodies, the continued influx
of pollution load is aggravated in summers when the water
evaporates and thereby increasing metal content. During
this process, many bacteria acquire metal tolerance (Ghosh
et al., 2000). Moreover, bacteria can also degrade and
detoxify a wide variety of hazardous compounds. Many
of these bacteria also carry plasmids (Silver and Misra,
1988; Mergeay, 1991). The role of plasmids in Pseudomonas sp. in the biotransformation of certain heavy metals,
pesticides and phenolics is also well documented (RajiniRani and Mahadevan, 1992; Deshpande et al., 2001; Thakur et al., 2001).
The ability of a genetic marker for transfer from one
bacterium to another through conjugation and/or transformation provides a good presumptive evidence for the
involvement of plasmid, particularly if the frequency of
transfer is high. Moreover, loss of certain genetic markers
as a result of treatment of bacterial cell to plasmid curing
agents also suggests for the plasmidial nature of the marker
(Mesas et al., 2004).
0045-6535/$ - see front matter 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2007.11.023
* Corresponding author. Tel.: +91 571 2700741; fax: +91 571 2706002.
E-mail addresses: sam_wasi@yahoo.com (S. Wasi), jeelani22@gmail.
com (G. Jeelani), smasood_ahmad@lycos.com (M. Ahmad).
www.elsevier.com/loc


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