Two major groups of colicin factors: their molecular weights

Bacteriocin release proteins: mode of action, structure, and biotechnological application

The mechanism by which Gram-negative bacteria like Escherichia coli secrete bacteriocins into the culture medium is unique and quite different from the mechanism by which other proteins are translocated across the two bacterial membranes, namely through the known branches of the general secretory pathway. The release of bacteriocins requires the expression and activity of a so-called bacteriocin release protein and the presence of the detergent-resistant phospholipase A in the outer membrane. The bacteriocin release proteins are highly expressed small lipoproteins which are synthesized with a signal peptide that remains stable and which accumulates in the cytoplasmic membrane after cleavage. The combined action of these stable, accumulated signal peptides, the lipid-modified mature bacteriocin release proteins (BRPs) and phospholipase A cause the release of bacteriocins. The structure and mode of action of these BRPs as well as their application in the release of heterologous proteins by E. coli is described in this review.

Virulence-related genes in ColV plasmids of Escherichia coli isolated from human blood and intestines

DNA probes for the colicin V, traT, iss, and iu genes were used in this study of four representative ColV plasmids together with 200 Escherichia coli strains isolated from the stools of patients with diarrhea and 146 E. coli strains isolated from the blood of patients with bacteremia. The study indicated that the ColV plasmids are heterogeneous. Southern and colony hybridization analyses showed that in most of the colicin V-producing intestinal E. coli strains, the colicin V genes are located in the chromosome (14 of 16); in most of the colicin V-producing E. coli strains isolated from the blood, they are located in plasmids (18 of 22). In both intestinal and blood E. coli isolates, the traT, iss, and aerobactin receptor genes were present at similar frequencies, but the frequency of the aerobactin synthesis genes was significantly different. The aerobactin receptor gene was present in 25% of the intestinal E. coli strains that lack the aerobactin synthesis gene. In the blood isolates, the aerobactin synthesis and receptor genes were present at almost equal frequencies. Among the colicin V-producing isolates, the iss, traT, and iu genes were present in 95.5, 86.4, and 90.9% of the blood isolates and in only 68.8, 43.8, and 81.3% of the intestinal isolates, respectively. The ColV plasmids from blood isolates that were tested for the presence of traT, iss, and iu genes were homogeneous and had DNA sequences that hybridized with each of the probes. On the other hand, the two intestinal strains containing ColV genes in a plasmid were heterogeneous in regard to the carriage of these genes. The presence of ColV is not restricted to specific O types.

The nucleotide sequences of the replication origins of plasmids ColA and ColD

The nucleotide sequences of the replication origin regions of plasmids ColA-CA31 and ColD-CA23 were obtained. Analysis of the nucleotide sequences showed a high degree of homology of these regions with the plasmid ColE1 region responsible for its autonomous replication. In the ColA and ColD regions involved in the regulation of replication, sites have been revealed identical to those participating in the transcription initiation of the ColE1 plasmid RNA I and primer RNA. The presumed RNA polymerase binding sites and the RNA polymerase recognition sequences are identical in ColA, ColD, and ColE1 plasmids. In spite of the differences in the nucleotide sequences, RNA I and the preprimer RNA of ColA and ColD may form structures analogous to the respective structures of ColE1.

Complete nucleotide sequence of the structural gene for colicin A, a gene translated at non-uniform rate

The complete nucleotide sequence of the structural gene for colicin A has been established. This sequence consists of 1776 base-pairs. According to the predicted amino acid sequence, the colicin A polypeptide chain comprises 592 amino acids and has a molecular weight of 62,989. The amino-terminal part is rich in proline and glycine and accordingly secondary structure prediction indicates that this region (1 to 185) is beta-structured. The rest of the molecule (residues 186 to 592) is very rich in alpha-helix. An uncharged amino acid sequence of 48 residues is located in the C-terminal part of the molecule, which is involved in the membrane depolarization caused by colicin A. A similar region has been found in colicin E1, which has the same mode of action as colicin A. Three peptides of these bacteriocins were found to be homologous, but a comparison of the bacteriocin genes did not reveal any significant homology out of the corresponding regions. The codon usage of both genes, however, exhibits some similarity and is quite different from that of genes coding for highly or weakly expressed proteins of Escherichia coli.

Physical map of pColA-CA31, an amplifiable plasmid, and location of colicin A structural gene

Evidence showing that the plasmic ColA, derived from strain CA31[pColA] can be amplified in the presence of chloramphenicol is presented. This plasmid has been purified and its Mr-value has been found to be 4.6 X 10(6) or 7 kb. Twelve cleavage sites have been mapped in pColA by using single and double restriction endonuclease digestions. These sites were ordered in relation to the single HindIII site. The other restriction endonucleases used were, respectively, SmaI, AvaI, PstI and HincII. Establishment of the map was helped by hybridization of pColA endonuclease digest products with 32P-labeled colicin A-mRNA. The structural gene for colicin A was contained in a 2.17-kb HincII fragment.

Serum resistance among Escherichia coli strains causing urinary tract infection in relation to O type and the carriage of hemolysin, colicin, and antibiotic resistance determinants

The sensitivity to normal human serum of 91 smooth strains of Escherichia coli isolated from urinary tract infections was determined. Production of hemolysin, which was common and associated primarily with the types O4, O6, O18, and O75, was significantly correlated with high levels of serum resistance, both within the total population and within individual O types. In contrast, serum resistance was not significantly associated with antibiotic resistance (whether transmissible or not), with colicinogeny in general, or with colicin V production in particular. This indicates that the carriage of R and ColV plasmids, shown previously to be capable of conferring increased levels of serum resistance on individual strains of E. coli isolated from other sources, does not play an important part in determining the serum sensitivity of the E. coli population involved in urinary tract infection.

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.

Spread of R-plasmids among Escherichia coli causing urinary tract infections

The incidence of multiple-antibiotic resistance among Escherichia coli isolated from urinary tract infections at Charing Cross Hospital, London, increased over the last 10 years, and its distribution was related to O-type. Among strains of the eight O-types most frequently causing such infections at this hospital, O4, O9, and O18 had a high incidence of multiple resistance (35, 22, and 19%, respectively); O2 and O6 had a intermediate incidence (14 and 11%, respectively); and O7, O1, and O75 had a low incidence (8, 6, and less than 3%, respectively). This nonrandom distribution appears to be a consequence of unequal plasmid recipient ability. After overnight mating with antibiotic-resistant donors, R-plasmid infection frequencies among antibiotic-sensitive urinary tract isolates differed by up to 10(5)-fold, and such differences were correlated with the variation in the incidence of antibiotic resistance among the O-types. The inherent differences in the ability to achieve significant R-plasmid spread, which appear to be determined by the host, not the plasmid, may be compounded in some cases by the inhibition of potential mating partners by colicin production.

Identification and characterization of Col plasmids from classical colicin E-producing strains

A series of transformants have been derived which carry the Col plasmids from 11 E-colicin-producing strains isolated by Fredericq or Hamon. The ColE plasmids identified included four of type E1, five of type E2, and two of a type designated E4 by Horak (Zentralbl. Bakteriol. Parasitenkd. Infektionskr. Hyg. Abt. 1 Orig. Reihe A 233:58-63, 1975). Strain K317 was shown to carry a ColE7 plasmid and a 2.7-megadalton (Md) ColE2imm plasmid which confers immunity to colicin E2 but not the ability to produce colicin. Other plasmids identified in the colicinogenic isolates were a 3.4-Md ColN plasmid and a 1.3-Md Col plasmid of unknown type. The ColE1 plasmids all continued replicating in cultures treated with chloramphenicol. Strains carrying the ColE4 or ColE3-CA38 plasmid exhibited partial sensitivity to their own colicins and exhibited an unusual clearing-zone morphology when overlaid on stabs of colicin E2- or E7-producing strains. Except for ColE1-K53, ColE1-K47, ColE2-CA42, and ColE7-K317, all of the ColE plasmids were found to be about 4.3 Md in size. ColE2-CA42 and ColE7-K317 are both about 3.9 Md and are the only two plasmids of the E2, E3, E4, and E7 types that did not yield a 0.39-Md deoxyribonucleic acid fragment as an EcoRI digestion product. The comparisons of the ColE plasmids suggest several structural and functional relationships among them.