Kinetics of colicin E2-induced solubilization and fragmentation of Escherichia coli DNA in vivo

Regulated breakdown of Escherichia coli deoxyribonucleic acid during intraperiplasmic growth of Bdellovibrio bacteriovorus 109J

During growth of Bdellovibrio bacteriovorus on [2-14C]deoxythymidine-labeled Escherichia coli, approximately 30% of the radioactivity was released to the culture fluid as nucleoside monophosphates and free bases; the remainder was incorporated by the bdellovibrio. By 60 min after bdellovibrio attack, when only 10% of the E. coli deoxyribonucleic acid (DNA) had been solubilized, the substrate cell DNA was degraded to 5 X 10(5)-dalton fragments retained within the bdelloplast. Kinetic studies showed these fragments were formed as the result of sequential accumulation of single- and then double-strand cuts. DNA fragments between 2 X 10(3) and 5 X 10(5) daltons were never observed. Chloramphenicol, added at various times after initiation of bdellovibrio intraperiplasmic growth on normal or on heated E. coli, which have inactivated deoxyribonucleases, inhibited further breakdown and solubilization of substrate cell DNA. Analysis of these intraperiplasmic culture deoxyribonuclease activities showed that bdellovibrio deoxyribonucleases are synthesized while E. coli nucleases are inactivated. It is concluded that continuous and sequential synthesis of bdellovibrio deoxyribonucleases of apparently differing specificities is necessary for complete breakdown and solubilization of substrate cell DNA, and that substrate cell deoxyribonucleases are not involved in any significant way in the degradation process.

Induction of lesions in deoxyribonucleic acid by low molecular weight substances from normal and colicin E2-treated cells of Escherichia coli

A fraction containing a variety of low molecular weight substances was extracted into 80% aqueous acetone from both a colicin E2-treated cell culture of Escherichia coli and an untreated one. The extract was divided into five fractions by Sephadex G15 chromatography. One of them, Fraction B, was separated into three subfractions by Sephadex G10 chromatography. Two subfractions, Fraction BI and Fraction BII, were further fractionated by several chromatographic systems. DNA was incubated with an aliquot from each of these fractions and was then analyzed by sedimentation in an alkaline sucrose density gradient. The activity which caused a decrease in the sedimentation coefficient of the DNA was found in some of these fractions. The activity from colicin E2-treated cells was compared with that from untreated ones. It was revealed that colicin E2 induces some increases in the activity toward DNA in one of the subfractions, Fraction BI, and also causes the appearance of a new species in another fraction, Fraction BII, which potentiates the activity in Fraction BI. These colicin E2-induced changes appeared at 5 min after the addition of colicin E2. The possible significance of such reactions for the action of colicin E2 are discussed.

Inhibtory effect of colicin E2 on transport systems of Escherichia coli in the presence of the rex gene of lambda prophage

Purified colicin E(2) was found to cause marked inhibition of the permeation rate of o-nitrophenyl-galactoside (ONPG) in several lambda-lysogenic strains of Escherichia coli in the presence of chloramphenicol to prevent prophage induction. The inhibitory effect of colicin E(2) on transport systems was analyzed with cells of E. coli CP78(lambda). The dose of colicin E(2) for the half-maximum inhibition of the ONPG-permeation rate was about 9 molecules of the colicin per bacterium under the aerobic condition, which corresponded to about 1 killing unit per bacterium. Kinetics of the transport of [(14)C]methylthiogalactoside suggested that colicin E(2) began to inhibit the influx rate of beta-galactosides within a few minutes after the colicin addition, and the maximum inhibition reached more than 80%. Extensive leakage of intracellular potassium ion and inhibition of l-proline transport also occurred at the same time. Acid solubilization of cellular deoxyribonucleic acid by the colicin was apparently delayed to the initiation of the transport inhibition. The extents of the inhibition of beta-galactoside transport and leakage of potassium ion by the colicin were extensive in cells lysogenic for wild lambda phage or lambdaind(-), whereas the extents were slight in the nonlysogenic cells or cells carrying lambdarex(-) prophage. It was concluded that the sensitization of membrane transport systems of E. coli cells to colicin E(2) was achieved by the presence of the rex gene product of lambda phage.

[Nature of bacteriocins]

The bacteriocins comprise a large, heterogeneous group of bactericidal substances produced by bacteria from widely differing species. The best known bacteriocins are the colicins. Some aspects of research on colicins are discussed especially their chemical nature and mode of action, and their genetic determinants.