Transcription of the Col E1 genome in colicinogenic E. coli strains during induction with mitomycin C

Bacteriocins: nature, function and structure

Bacteriocins are extracellular substances produced by different types of bacteria, including both Gram positive and Gram negative species. They can be produced spontaneously or induced by certain chemicals such as mitomycin C. They are biologically one of the important substances, and have been found to be useful in membrane studies and also in typing pathogenic microorganisms causing serious nosocomial infections. Bacteriocins are a heterogeneous group of particles with different morphological and biochemical entities. They range from a simple protein to a high molecular weight complex: the active moiety of each molecule in all cases seems to be protein in nature. The genetic determinants of most of the bacteriocins are located on the plasmids, apart from few which are chromosomally encoded. These bactericidal particles are species specific. They exert their lethal activity through adsorption to specific receptors located on the external surface of sensitive bacteria, followed by metabolic, biological and morphological changes resulting in the killing of such bacteria. This review summarises the classification, biochemical nature, morphology and mode of action of bacteriocins as well as their genetic determinants and the microbiological relevance of these bactericidal agents.

Interfaces of the yeast killer phenomenon

A new prophylactic and therapeutic antimicrobial strategy based on a specific physiological target that is effectively used by killer yeasts in their natural ecological competition is theorized. The natural system exploited is the yeast killer phenomenon previously adopted as an epidemiological marker for intraspecific differentiation of opportunistic yeasts, hyphomycetes, and bacteria. Pathogenic microorganisms (Candida albicans) may be susceptible to the activity of yeast killer toxins due to the presence of specific cell wall receptors. On the basis of the idiotypic network, we report that antiidiotypic antibodies, produced against a monoclonal antibody bearing the receptor-like idiotype, are in vivo protecting animals immunized through idiotypic vaccination and in vitro mimicking the antimicrobial activity of yeast killer toxins, thus acting as antibiotics.

Transcription regulation of colicin Ib synthesis

Bacteriophage Mud (Casadaban and Cohen 1979) was used to bring the transcription of the gene for beta galactosidase (lacZ) under the control of the promoter of the structural gene for colicin Ib (cia(Ib)) on a derivative of the Col plasmid Col-Ib.P9. Transcription of this fusion operon was stimulated by agents which damaged cellular DNA (mitomycin C, bleomycin and colicin E2). Increased transcription of the cia-lacZ operon could be detected within 13 min of the addition of these agents. In a strain bearing the tif-1 (recA441) mutation, constitutive expression of the SOS DNA repair system at 42 degree C also increased transcription of the cia-lacZ operon. Transcription of the cia-lacZ operon was also stimulated by inhibition of DNA gyrase activity with nalidixic acid but not with novobiocin. Transitory inhibition of protein synthesis with chloramphenicol or by proline starvation of a proline auxotroph did not stimulate cia-lacZ transcription. Transcription of the cia-lacZ operon was substantially reduced in the presence of a recA mutation, but was largely unaffected by a mutation in recB affecting the RecBC DNase or by catabolite repression. Control experiments in which the production of colicin Ib was measured confirmed that the experiments with the fusion operon gave an accurate indication as to the activity of the wild type cia gene except for the effect of catabolite repression, where we observed up to 99% reduction in colicin Ib production in strains carrying mutant crp or cya alleles. The overall results confirm previous suggestions that there was considerable similarity between the regulatory systems controlling production of colicins and the repressor-dependent regulation of lambdoid prophage induction.

The fate of a bacterial plasmid in mammalian cells

When hamster cells are infected with the bacterial plasmid colicinogenic factor E1 (ColE1), as much as 5-8% of the input plasmid radioactivity is found in the recipient cell, mainly in the nuclear fraction. Density shift experiments with bromodeoxyuridine labeled ColE1 DNA indicate that part of the input DNA may be replicated in the nucleus. ColE1 specific RNA but no colicin E1, can be detected during the first two generations after the uptake of ColE1 DNA. However, extrachromosomal ColE1 DNA is unstable in the mammalian cells and is degraded to acid soluble fragments after a few generations.