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M Dua

Publications and source records attributed to M Dua.

9 recordsLinked to original sources
PubMed2002

Biotechnology and bioremediation: successes and limitations.

With advances in biotechnology, bioremediation has become one of the most rapidly developing fields of environmental restoration, utilizing microorganisms to reduce the concentration and toxicity of various chemical pollutants, such as petroleum hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phthalate esters, nitroaromatic compounds, industrial solvents, pesticides and metals. A number of bioremediation strategies have been developed to treat contaminated wastes and sites. Selecting the most appropriate strategy to treat a specific site can be guided by considering three basic principles: the amenability of the pollutant to biological transformation to less toxic products (biochemistry), the accessibility of the contaminant to microorganisms (bioavailability) and the opportunity for optimization of biological activity (bioactivity). Recent advances in the molecular genetics of biodegradation and studies on enzyme-tailoring and DNA-shuffling are discussed in this paper.

Biodegradation, Environmental↗
PubMed2000

The importance of homologous recombination in the generation of large deletions in hybrid plasmids in Amycolatopsis mediterranei.

The cloning vector pRL60 was developed previously as a tool for genetic manipulations in Amycolatopsis mediterranei, which produces the commercially and medicinally important antibiotic rifamycin. Here, a method based on intraplasmid recombinations is described for the construction of smaller plasmids in A. mediterranei, which also helped in delimiting the origin of replication (pA-rep) of the parent plasmid. The strategy involved the cloning of a selectable marker, erythromycin resistance gene (ermE), onto plasmids pULAM2 and pULVK2A (derivatives of pRL1), followed by selection of the hybrid or concatemeric plasmids pRL50 and pRL80 (with large homologous repeats) in Escherichia coli GM2163. These hybrid plasmids were then transferred to A. mediterranei DSM 40773 by electroporation, with selection in the presence of different antibiotics. During the process of transformation and selection in A. mediterranei, pRL50 and pRL80 underwent intraplasmid recombinations, yielding derivatives that retained a common region essential for maintenance and replication, as well as the selected resistance genes. This approach produced several smaller plasmids designated pRL51, pRL52, pRL53, pRL60, pRL81, and pRL82. These plasmids, isolated from A. mediterranei DSM 40773, could be transferred to different Amycolatopsis strains at transformation efficiencies ranging from 0.7 x 10(2) to 4 x 10(4) transformants/microg DNA. The electroporation parameters under which maximum transformation efficiencies were obtained varied from strain to strain. Since the isolation of plasmid DNA from Amycolatopsis strains were extremely difficult, a convenient and rapid method of direct transfer of plasmid DNA, i.e., electroduction, was also developed in which the above-described shuttle plasmids were transferred directly from A. mediterranei to E. coli. In addition, the sequence of the minimal (pA-rep, approximately 1.0 kb) of plasmid pRL51 was determined. The nucleotide base sequence of the pA-rep region did not have any clear similarity to the DNA or amino acid sequences in various databases, suggesting that it is unique.

Actinomycetales↗
PubMed2000

Enhanced degradation of hexachlorocyclohexane isomers by Sphingomonas paucimobilis.

Hexachlorocyclohexane (HCH) has been banned for use in technologically advanced countries; however, it is still in use in tropical countries like India. Earlier we reported the degradation of HCH isomers by Sphingomonas paucimobilis within 12 days of incubation. Here we report the role of different factors that could enhance the degradation rate of HCH isomers. We found that an increase in the cell number from 10(2) to 10(8) cells/ml resulted in an increased degradation rate of HCH isomers viz. alpha, beta, gamma, and delta-HCH. While alpha-HCH and gamma-HCH disappeared completely from the medium within 3 days of incubation, a maximum of only 90% and 85% degradation was observed for beta and delta-HCH, respectively. We have also observed that adapted cultures degraded HCH isomers more efficiently than did the normal cultures.

Biodegradation, Environmental↗
PubMed1999

Characterization and regulation of catabolic genes.

Although a wide range of microorganisms have been discovered that are able to degrade highly stable, toxic xenobiotics, still many pollutants persist in the environment. Recent advances in the field of r-DNA technology has provided solutions to these problems. One important factor limiting the bioremediation of sites contaminated with certain hazardous wastes is the slow rate of degradation. This slow rate limits the practicality of using bacteria in remediating contaminated sites. It is possible to extend the range of substrates that an organism can utilize. It is even possible to endow an organism with the ability to degrade a predetermined range of xenobiotics. Because biotechnological processes are based on natural activities of microorganisms and constitute variations in classic domestic waste treatment processes, they are publicly more accepted. This is an area where genetic engineering can make a marked improvement by manipulating catabolic genes of microorganisms. Advances in r-DNA technology have opened up new avenues to move toward the goal of genetically engineered microorganisms to function as "designer biocatalysts" in which certain desirable biodegradation pathways or enzymes from different organisms are brought together in a single host with the aim of performing specific detoxification. In the last 2 decades much progress has been made in this direction, and as a result catabolic genes have been cloned and characterized for organochlorines, polychlorinated biphenyls, chlorobenzoates, naphthalene etc. The aim of this review is to provide an insight in the recent advances made on characterization and expression of catabolic genes that encode the degradation/detoxification of these persistent and toxic xenobiotic compounds.

Anthracenes↗
PubMed1998

Selection of suitable marker genes for the development of cloning vectors and electroporation in different strains of Amycolatopsis mediterranei.

To select suitable genetic markers for optimizing electroporation efficiency in Amycolatopsis mediterranei, thiostrepton (tsr), erythromycin (ermE) and apramycin (am) resistance genes were used. Although tsr could not be suitably expressed in A. mediterranei, the cloning of ermE in pRL1 or its derivative (containing am) resulted in the development of cloning vectors pRLM20, pRLM30 and pRL90. In contrast to tsr and km (kanamycin resistance gene), ermE and am were suitably expressed in A. mediterranei strains and no spontaneous mutants were observed among transformants. Under optimum conditions, maximum electroporation efficiency of 1.2 x 10(4) transformants/micrograms DNA was achieved for A. mediterranei DSM 40,773. These plasmids could also be effectively transferred in other strains of A. mediterranei including F1/24 and T-195. With the cloning of ermE and am and their expression in different strains of Amycolatopsis, we have overcome the problem of the choice of suitable selectable markers for A. mediterranei and related species.

Actinomycetaceae↗
PubMed1996

Genetic manipulations of microorganisms for the degradation of hexachlorocyclohexane.

Hexachlorocyclohexane (HCH) is an organochlorine insecticide which has been banned in technologically advanced countries. However, it is still in use in tropical countries for mosquito control and thus new areas continue to be contaminated. Anaerobic degradation of HCH isomers have been well documented but until recently there have been only a few reports on aerobic microbial degradation of HCH isomers. The isolation of these microbes made it possible to design experiments for the cloning of the catabolic genes responsible for degradation. We review the microbial degradation of HCH isomers coupled with the genetic manipulations of the catabolic genes. The first part discusses the persistence of residues in the environment and microbial degradation while the second part gives an account of the genetic manipulations of catabolic genes involved in the degradation.

Bacteria↗