Preparation and purification of DNA from bacterial cells; characterization of plasmid DNA

Author(s): M. Praveen, G. Adarsh, T. Ramesh, M. Ramesh*

Abstract

The use of genetic material to deliver genes for therapeutic purposes has been practiced for many years. With the advancement in genetic engineering, foreign genes of industrial applications can be inserted into cloning vector for mass production in various host cells. Escherichia coli is an extremely important model organism in modern biological engineering, the suitable growth media is essential for the optimal expression of the genes in E. coli. The present study aims at isolation and purification of genomic DNA from E. coli, the characterization of pBR322 plasmid DNA. Bacterial culture conditions were optimized in shake – flask cultures based on optimal temperature, inoculum size and medium composition. Solutions and methods are disclosed for the effective, simple isolation of DNA from bacterial cells. High bioprocess recovery and product quality were primarily associated with the complete removal of total cellular RNA impurity. The process was demonstrated without the use of animal-derived RNase. High-molecular-weight (HMW) RNA and other impurities were removed by selective precipitation using calcium chloride at an optimal concentration. The optimal conditions for the growth of Escherichia coli were shown maximum absorbance as 7.5 at 370C temperature, 1% inoculum size using TB medium composition. The purified genomic DNA had concentration as 73.5 µg/ml and purity 1.8. The 0.5M CaCl2 was optimal concentration for removal of RNA. The plasmid DNA pBR322 was confirmed by comparing the band to 4.36 Kb, purity of plasmid was 1.85 and it contains 96.8% of super coiled DNA. The contaminants like chromosomal DNA, RNA, host cell proteins and mycoplasma were absent in the plasmid DNA.

image 10.21746/ijbio.2013.01.001

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