The Effects of Pretreatment of Competent Cells with Nalidixic Acid on Efficiency of Chemically-Induced Transformation in Escherichia coli B23

Abstract

Transformation of Escherichia coli with foreign DNA is dependent on DNA binding and translocation at the cell surface. Nalidixic acid is an antibacterial agent that disrupts DNA replication and arrests the cell cycle, resulting in elongated, serpentine cell forms. This study investigated the effect of increased cell surface area, produced by exposure to nalidixic acid, on the transformation efficiency of E. coli. E. coli B23 cells were either treated with a sublethal dose of nalidixic acid or left untreated, then transformed with a plasmid encoding ampicillin resistance by using a calcium chloride/heat shock method. Cells treated with nalidixic acid had -10 a transformation frequency of 5.6 x 10 cfu/ μ g per viable cell while untreated cells had a -10 transformation frequency of 53 x 10 cfu/ μ g per viable cell. Our results demonstrate that cell elongation caused by nalidixic acid decreases transformation efficiency and suggest that this is due to lower viability following heat shock.