Colicins and related bacteriocins

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Solute and Ion Transport: Outer Membrane Pores and Receptors

Two membranes enclose Gram-negative bacteria-an inner membrane consisting of phospholipid and an outer membrane having an asymmetric structure in which the inner leaflet contains phospholipid and the outer leaflet consists primarily of lipopolysaccharide. The impermeable nature of the outer membrane imposes a need for numerous outer membrane pores and transporters to ferry substances in and out of the cell. These outer membrane proteins have structures distinct from their inner membrane counterparts and most often function without any discernable energy source. In this chapter, we review the structures and functions of four classes of outer membrane protein: general and specific porins, specific transporters, TonB-dependent transporters, and export channels. While not an exhaustive list, these classes exemplify small-molecule transport across the outer membrane and illustrate the diversity of structures and functions found in Gram-negative bacteria.

Biomedical applications of fermenticin HV6b isolated from Lactobacillus fermentum HV6b MTCC10770

Fermenticin HV6b is a class IIa antimicrobial peptide produced by Lactobacillus fermentum HV6b MTCC 10770 isolated from human vaginal ecosystem. It shows growth inhibition of a wide range of opportunistic pathogens of humans, for example, Bacteroides, Gardnerella vaginalis, Mobiluncus, Staphylococci, and Streptococci, associated with bacterial vaginosis in humans. It does possess an impressive sperm immobilization and spermicidal activity tested against human sperms which makes it an attractive proposition for formulating antibacterial vaginosis and contraceptive products. Apart from this, in vitro studies conducted against four different tissue models have indicated its potential to be used as a component of anticancerous drug therapy as it is reported to induce apoptosis in cancerous cells. This information could be integrated in future studies focusing on in vivo assessment of anticancerous activity of lactic acid bacterial toxins or bacteriocins.

Translocation trumps receptor binding in colicin entry into Escherichia coli

Of the steps involved in the killing of Escherichia coli by colicins, binding to a specific outer-membrane receptor was the best understood and earliest characterized. Receptor binding was believed to be an indispensable step in colicin intoxication, coming before the less well-understood step of translocation across the outer membrane to present the killing domain to its target. In the process of identifying the translocator for colicin Ia, I created chimaeric colicins, as well as a deletion missing the entire receptor-binding domain of colicin Ia. The normal pathway for colicin Ia killing was shown to require two copies of Cir: one that serves as the primary receptor and a second copy that serves as translocator. The novel Ia colicins retain the ability to kill E. coli, even in the absence of receptor binding, as long as they can translocate via their Cir translocator. Experiments to determine whether colicin M uses a second copy of its receptor, FhuA, as its translocator were hampered by precipitation of colicin M chimaeras in inclusion bodies. Nevertheless, I show that receptor binding can be bypassed for killing, as long as a translocation pathway is maintained for colicin M. These experiments suggest that colicin M, unlike colicin Ia, may normally use a single copy of FhuA as both its receptor and its translocator. Colicin E1 can kill in the absence of receptor binding, using translocation through TolC.

Mechanism of colicin action: early events

The kinetics and the temperature dependence of potassium loss from Escherichia coli cells treated with colicin K have been examined. At 37 C, after a single lethal hit, essentially all of the intracellular potassium is lost within the first few minutes of treatment. The initial rate of loss is linearly related to colicin concentration up to a multiplicity of 30. As the temperature is decreased over the range from 37 to 1 C, an increasing delay is seen in the initiation of potassium loss after colicin adsorption. This delay can be overcome by increasing colicin multiplicity and probably reflects an alteration of the cell membrane at these temperatures. A comparison of this effect with an apparently related effect of temperature on the action of irehdiamine A indicates that the delay may represent the inhibition of a transmission process occurring in the membrane.

Mode of Action of Vibriocin: Initial Interaction with Vibrio comma Cells

Certain metabolic requirements, upon initial interaction of sensitive cells with vibriocin, were a prerequisite for lethal activity. Transient "immunity" of these cells, manifested under suboptimal growth conditions, differed from the immunity of vibriocinogenic cells.

Inhibition of colicin e2 activity by bacterial lipopolysaccharide

Lipopolysaccharide isolated from colicin E2-sensitive Escherichia coli and from "receptor-minus" mutants inhibits the activity of colicin E2. Lipid A and the polysaccharide fraction obtained by mild acid hydrolysis of lipopolysaccharide are inactive either alone or when tested in combination. Periodate oxidation of lipopolysaccharide destroys over 85% of its inhibition activity.

The dual role of bacteriocins as anti- and probiotics

Bacteria employed in probiotic applications help to maintain or restore a host's natural microbial floral. The ability of probiotic bacteria to successfully outcompete undesired species is often due to, or enhanced by, the production of potent antimicrobial toxins. The most commonly encountered of these are bacteriocins, a large and functionally diverse family of antimicrobials found in all major lineages of Bacteria. Recent studies reveal that these proteinaceous toxins play a critical role in mediating competitive dynamics between bacterial strains and closely related species. The potential use of bacteriocin-producing strains as probiotic and bioprotective agents has recently received increased attention. This review will report on recent efforts involving the use of such strains, with a particular focus on emerging probiotic therapies for humans, livestock, and aquaculture.

Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import

Colicin Ia is a 69 kDa protein that kills susceptible Escherichia coli cells by binding to a specific receptor in the outer membrane, colicin I receptor (70 kDa), and subsequently translocating its channel forming domain across the periplasmic space, where it inserts into the inner membrane and forms a voltage-dependent ion channel. We determined crystal structures of colicin I receptor alone and in complex with the receptor binding domain of colicin Ia. The receptor undergoes large and unusual conformational changes upon colicin binding, opening at the cell surface and positioning the receptor binding domain of colicin Ia directly above it. We modelled the interaction with full-length colicin Ia to show that the channel forming domain is initially positioned 150 A above the cell surface. Functional data using full-length colicin Ia show that colicin I receptor is necessary for cell surface binding, and suggest that the receptor participates in translocation of colicin Ia across the outer membrane.

Purification and characterization of pertucin produced by Pseudomonas pertucinogena

Pertucin, a bacteriocin active against phase I organisms of Bordetella pertussis, was extracted from Pseudomonas pertucinogena, strain 190 or 6627, by freezing and thawing of bacteria-free agar medium and was purified by ammonium sulfate fractionation, dialysis, zinc chloride precipitation, and polyacrylamide gel electrophoresis. The specific activity of purified pertucin was approximately 80 times that of the crude extract. The purified pertucin preparation was homogeneous on ultracentrifugal analysis and polyacrylamide gel electrophoresis, and was found to be composed of protein (80%) and carbohydrate (20%), the latter assumed not to be bound covalently to the protein. Neither nucleic acids nor lipids were demonstrated. N-terminal analysis by dansylation revealed only methionine in strain 190 and only glycine in strain 6627. The isoelectric point was found to be 4.8, and the molecular weight was estimated to be 31,500. Amino acid analysis of the protein moiety demonstrated that it contained all of the common amino acids with somewhat more of the hydrophilic amino acids. With respect to thermostability, pH stability, and effects of metal ions and various buffers, pertucin behaves like a protein and is stable in 0.05 M tris(hydroxymethyl)aminomethane buffer, pH 8.0, containing 0.01 M Ca(2+).

Characterization of two antagonistic strains ofRahnella aquatilis isolated from soil in egypt

In an attempt to obtain biological control agents for controlling bacterial spot of cucumber, over 250 bacterial strains were isolated from agricultural soil samples, collected from different localities in Giza Governorate (Egypt) and screened for in vitro antibiosis towards Xanthomonas campestris. Only 2 strains showed antagonistic activity. They and their culture filtrates restricted the growth of a number of G- and G(+)-indicator bacteria. On Chrome Azurol S agar, both strains exhibited a marked siderophore production. Biolog plates identified these strains as Rahnella aquatilis. Their characteristics were studied and compared with literature data on R. aquatilis. This antagonistic bacterium has not been previously isolated in Egypt.

Crystal structure of colicin E3: implications for cell entry and ribosome inactivation

Colicins kill E. coli by a process that involves binding to a surface receptor, entering the cell, and, finally, intoxicating it. The lethal action of colicin E3 is a specific cleavage in the ribosomal decoding A site. The crystal structure of colicin E3, reported here in a binary complex with its immunity protein (IP), reveals a Y-shaped molecule with the receptor binding domain forming a 100 A long stalk and the two globular heads of the translocation domain (T) and the catalytic domain (C) comprising the two arms. Active site residues are D510, H513, E517, and R545. IP is buried between T and C. Rather than blocking the active site, IP prevents access of the active site to the ribosome.

Crystal structure of colicin E3 immunity protein: an inhibitor of a ribosome-inactivating RNase

BACKGROUND

Colicins are antibiotic-like proteins of Escherichia coli that kill related strains. Colicin E3 acts as an RNase that specifically cleaves 16S rRNA, thereby inactivating the ribosomes in the infected cell. The producing organism is protected against colicin E3 by a specific inhibitor, the immunity protein Im3, which forms a tight 1:1 complex with colicin E3 and renders it inactive. Crystallographic studies on colicin E3 and Im3 have been undertaken to unravel the structural basis for the ribonucleolytic activity and its inhibition.

RESULTS

The crystal structure of Im3 has been determined to a resolution of 1.8 A. The structure consists of a four-standard antiparallel beta sheet flanked by three alpha helices on one side of the sheet. Thr7, Phe9, Phe16 and Phe74 form a hydrophobic cluster on the surface of the protein in the vicinity of Cys47. This cluster is part of a putative binding pocket which also includes nine polar residues.

CONCLUSIONS

The putative binding pocket of Im3 is the probable site of interaction with colicin E3. The six acidic residues in the pocket may interact with some of the numerous basic residues of colicin E3. The involvement of hydrophobic moieties in the binding is consistent with the observation that the tight complex can only be dissociated by denaturation. The structure of Im3 resembles those of certain nucleic acid binding proteins, in particular domain II of topoisomerase I and RNA-binding proteins that contain the ribonucleoprotein (RNP) sequence motif. This observation suggests that Im3 has a nucleic acid binding function in addition to binding colicin E3.

Characterization and plasmid profile of an inhibitory strain of Erwinia herbicola isolated from Phaseolous vulgaris in Egypt

Erwinia herbicola strain 48 was isolated from diseased phaseolous seedlings and characterized by biochemical properties, cellular fatty acid analysis and SDS-PAGE of the soluble cell protein. Although cellular fatty acid profile and the soluble cellular protein pattern showed high degree of similarity in comparison to those from E. herbicola strain 347417, obtained from the International Mycological Institute U.K., plasmid profiles were different. Both strains harbor a 23.1 kb plasmid, in addition, E. herbicola 48 contains 2 more plasmids (26.8 and 32.5 kb). The antagonism of E. herbicola 48 against a number of Gram-negative and Gram-positive bacteria was tested in vitro. Only Gram-negative bacteria were inhibited, suggesting that the inhibitory factor is likely to be bacteriocin.

Mode of action of a lysostaphin-like bacteriolytic agent produced by Streptococcus zooepidemicus 4881

Electron microscopy of zoocin A-treated sensitive streptococcus cells revealed cytoplasmic disruption and ultimately complete rupture of the cell wall. Culture viability and optical density were shown to decrease rapidly and simultaneously in Streptococcus pyogenes FF22 but less quickly in the relatively more resistant Streptococcus mutans 10449. Zoocin A was shown to cleave hexaglycine in a colorimetric cell-free microtiter assay system, and it is concluded that the killing action of zoocin A, like that of lysostaphin, is most probably the result of direct cleavage of the peptidoglycan cross-links in the cell wall. The relationship between sensitivity to zoocin A and the peptidoglycan cross-linkage structure of Streptococcus zooepidemicus, Lactococcus spp., S. pyogenes, Streptococcus gordonii, Streptococcus oralis, S. mutans, and Streptococcus rattus has been evaluated.

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.

Construction and characterization of pyocin-colicin chimeric proteins

Chimeric proteins were constructed from pyocin S1 or S2 and colicin E3 or E2, and their characteristics were investigated with special reference to the domain structure. The nuclease domains were interchangeable between two bacteriocins so that a new kind of pyocin, with RNase activity, was created. A bacteriocin which can kill both Pseudomonas aeruginosa and Escherichia coli was also constructed. Investigations with various chimeric proteins indicate that the translocation domain as well as the receptor-binding domain is species specific. Inhibition of lipid synthesis, which is characteristic of pyocins, was also observed with chimeric pyocins carrying the DNase domain of colicin E2 but not with those carrying the RNase domain of E3. Thus, the DNase domain is responsible for the inhibition of lipid synthesis.

Partial purification and characterization of bacteriocin from Yersinia kristensenii

A raw milk bacterial isolate, identified as Yersinia kristensenii was found to produce a bacteriocin which was inhibitory to Yersinia enterocolitica but not to other selected species of Yersinia or Gram-negative bacteria. Maximum production of bacteriocin was obtained when the organism was grown in shake culture at 28 degrees C. Mitomycin C at a concentration of 0.5 micrograms ml-1 induced bacteriocin production. The bacteriocin was partially purified and characterized by ammonium sulphate fractionation and gel filtration. The bacteriocin was completely inactivated when treated with proteolytic enzymes (trypsin and chymotrypsin). Bacteriocin activity was heat-resistant and it retained some of its activity after 5 min at boiling temperature. A total of 15 bacteriocin sensitive-suspected food isolates were further identified biochemically as Yersinia enterocolitica and a non-sensitive isolate was identified as Yersinia intermedia.

Antimicrobial effect of fermented Ghanaian maize dough

Unhygienic conditions of a typical rural community in a developing country were simulated in the laboratory by inoculating fermented maize dough porridge with Shigella flexneri and enterotoxigenic Escherichia coli (ETEC). The antimicrobial effects of the different processes involved in the preparation of fermented maize dough porridge were assessed. The soaking process reduced the pH but no antimicrobial effect against shigella and ETEC was noted. Unfermented maize dough did not inhibit any of the test strains. When the fermentation process had become established, half of the strains tested were inhibited by the fermented maize dough when examined 8 h after inoculation. Cooking the fermented maize dough into porridge reduced the antimicrobial effect but there was still significant inhibition of pathogens. This suggests that the antimicrobial effect of fermented maize dough is not due to pH per se. Fermentation of maize dough appears to be a useful strategy for reducing contamination of weaning foods by Sh. flexneri and ETEC. The possible nature of the antimicrobial agent(s) produced during the fermentation of maize dough is discussed.

Evidence for a chromosomally determined bacteriocin production by Klebsiella pneumoniae

Location of the genes responsible for pneumocin production in Klebsiella pneumoniae was examined by classical procedures. Conjugal intrageneric transfers, elimination experiments with various curing agents, high temperature and plasmid isolation procedures showed that this strain did not harbour any plasmid. Hence chromosomal location of the genetic determinants is suggested.

Bacteriocin involved in premature death of Lactobacillus acidophilus NCFM during growth at pH 6

Lactobacillus acidophilus NCFM maintained at pH 6 during growth in lactobacilli MRS broth appeared to exhibit premature death. However, during extended incubation, the culture reinitiated growth. Spent broth collected from the culture when it began the premature death was very toxic to the culture, but growth did occur during extended incubation of the assay tubes. When several successive subcultures with extended incubation were made in MRS broth containing added inhibitory spent broth, a strain (identified as L. acidophilus) was isolated that was resistant to the inhibitor. This strain produced a bacteriocin that was inhibitory to the growth of L. acidophilus NCFM and the predominating strains isolated from it. The producer strain grew more slowly than did the predominating strains in culture NCFM. The results show that when L. acidophilus NCFM, a mixed strain culture, was grown at pH 6, the inhibitory strain was able to grow sufficiently to produce enough bacteriocin to destroy the predominating strain(s) in the culture.

Colicin E1 in planar lipid bilayers

The channel formed by the C-terminal domain of colicin E1 in planar lipid bilayers has proven to be more complex than one might have guessed for such a simple system. The protein undergoes a pH-dependent rearrangement which transforms it from a water soluble form to a much different membrane bound form. There are at least two bound states which don't form a channel. The process by which the channel opens and closes is regulated by the pH and the transmembrane voltage. The voltage is probably sensed by at least 3 (and more likely 4 or more) lysine residues which must be driven through the field to open the channel. The process appears to be hindered by particular carboxyl groups when they are in the unprotonated state. The open channel has several substates and several superstates. Very large positive voltage catalyzes a transition of the open channel to an inactivated state, and may be able to drive the channel-forming region of the protein across the membrane. Little is known about the structure of any of these states, but the open channel is large enough to allow NAD to traverse the membrane and appears to be formed by one colicin molecule. This single polypeptide mimics many of the properties found in channels of mammalian cell membranes, but it may prove more relevant as a model for the transport of proteins across membranes. The comparative ease with which the protein can be manipulated chemically and genetically, along with the complexity of its behavior, promises to keep several laboratories busy for some time.

Recognition of T-cell murine leukemia by bacteriocin (colicin); correlation with transplantation experiments

The presence of potential murine leukemia and overt leukemia cells in various organs at different phases of leukemogenesis was demonstrated by transplantation experiments and sensitivity to bacteriocin (colicin HSC10). Such correlation was found in three experimental models: AKR mice developing spontaneous T-cell leukemia and BL/6 mice infected with radiation leukemia virus variants inducing a high or low overt T-cell leukemia incidence. The sensitivity to bacteriocin was evaluated by testing the cell cycle perturbation following in-vitro incubation of lymphoid cells with colicin (or Tris buffer as controls) monitored by flow-cytometry. The analysis was based on measuring relative differences in fluorescence intensity of propidium iodide stained DNA in the individual cells. The interaction with colicin of leukemic cells and lymphoid cells containing potential leukemic cells (PLC) resulted in a reduction in the cell number of the G0/G1 and SG2M phases while cells accumulated in the "pre-G1" channels. In contrast, normal lymphoid cells exposed to bacteriocin did not show such changes in the DNA histograms. The distribution pattern of PLC in the thymus and spleen (in the models tested) obtained by transplantation studies coincided with sensitivity of spleen and thymus cells to colicin. However, in most instances, the PLC in the bone marrow were not recognized by colicin, but their leukemogenic potential was reduced following interaction with colicin as shown by PLC transplantation studies. It is thus suggested that colicin might be used for identification and eradication of transformed cells.

Purification and characterization of the Lactobacillus acidophilus bacteriocin lactacin B

Parameters for production and purification of a bacteriocin produced by Lactobacillus acidophilus N2 are described. Production of lactacin B was pH dependent, with maximum activity detected in broth cultures maintained at pH 6. Lactacin B was purified by ion-exchange chromatography, ultrafiltration, and successive gel filtrations in the presence of 8 M urea and then 0.1% sodium dodecyl sulfate. The molecular weight of lactacin B was ca. 6,000 to 6,500, and the purified compound showed maximum absorbance at 211 nm. The activity of purified lactacin B was bactericidal to sensitive cells and restricted to members of the family Lactobacilliaceae, L. leichmannii, L. bulgaricus, L. helveticus, and L. lactis. Characteristics identified for lactacin B indicated that it was a peptide and confirmed its identity as a bacteriocin.

Purification and characterization of a bacteriocin from Bacteroides fragilis

A bacteriocin produced by Bacteroides fragilis 1356 was purified from culture medium and characterized. The spectrum of the inhibitory activity of this bacteriocin was species specific. The bacteriocin was recovered from the initial stages of purification as a complex, greater than 2 X 10(7) daltons in mass, containing protein, lipid, and carbohydrate. The dissociation of this complex by 6.0 M guanidine hydrochloride permitted further purification of the bacteriocin by removal of lipid and carbohydrate. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the purified bacteriocin was homogeneous, with a relative molecular weight of 5,000. The activity of the purified bacteriocin was not affected by RNase, DNase, phospholipase A, pancreatic lipase, or dextranase, but was destroyed by trypsin, proteinase K, heat (80 degrees C, 30 min), or a pH below 5 or above 8. Amino acid analysis indicated a predominance of acidic and polar amino acids.

Production of a bacteriocin, ulceracin 378, by Corynebacterium ulcerans

The production of the bacteriocin ulceracin 378 by Corynebacterium ulcerans 378 was demonstrated during the growth of the organism on solid medium. Ulceracin 378 was not found in broth cultures and could not be extracted from the organisms by various solvents and salt solutions. Ulceracin 378 was not inducible by UV irradiation or mitomycin C treatments. Ulceracin 378 was active against all of the C. ulcerans strains tested and some related species, but it was not autoinhibitory. The active material was not phage related and was extracted from cultures grown on semisolid media composed of proteose peptone, Tween 80, Casamino Acids, glycerol, and sodium chloride. The yield was significantly reduced by either increasing the agar concentration or omitting Tween 80. Ulceracin 378 was resistant to DNase, RNase, phospholipases C and D, and alkaline phosphatase but was susceptible to proteolytic enzymes. This suggests that the active principle of ulceracin is protein in nature. Ulceracin 378 was partially purified by ammonium sulfate fractionation, dialysis, and chromatography on DEAE-cellulose.

Bacteriocin and flow cytometry in laboratory diagnosis of leukemic peripheral blood lymphocytes and bone marrow cells

The bacteriocin, colicin HSC10, produced by Escherichia coli HSC10, was studied as a laboratory tool for detection and differentiation of leukemic from normal lymphocytes in human peripheral blood. Flow cytometry studies detected DNA loss in bacteriocin-affected cells by computerized histograms. Differential analysis is given for the peripheral blood of 26 individuals using bacteriocin, cytochemistry and surface markers. Sensitivity to colicin was detected in 10 (83%) of the 12 patients with chronic lymphocytic leukemias and other leukemias with morphologically immature lymphocytes. Cells were lost from the G0/G1 phase and accumulated in the 'pre-G1' channels of the histogram, indicative of cells with reduced DNA content. The lymphocytes of 14 normals, however, were not or only slightly affected by the bacteriocin (P less than 0.001). Similarly, normal bone marrow cells exposed to bacteriocin remained unaffected (P greater than 0.2). Thus, immaturity per se was not recognized by bacteriocin. The bacteriocin effect was more discriminatory than other laboratory tests reported here and in most cases differentiated malignant from normal cells.

An epidemiological study of Serratia marcescens infections by bacteriocin typing

Bacteriocin sensitivity typing according to the method of Traub (Appl. Microbiol. 1971. 21: 837-840) was carried out on 226 clinical isolates of Serratia marcescens obtained from inpatients at Nagasaki University Hospital during the period from January 1976 to December 1978. The isolates were divided into 16 different bacteriocin types, mainly 26, 4, and 9. The distribution of the types suggests that Serratia marcescens infections may be caused by cross infection. Reproducibility of bacteriocin typing and the relationship between serotypes (O-antigen) and bacteriocin types are discussed in regard to the application of this method to the study of nosocomial infections.

Cloning of colicin E1 tolerant tolC (mtcB) gene of Escherichia coli K12 and identification of its gene product

A mutation in the tolC(mtcB) gene of Escherichia coli K12 results in increased sensitivity to sodium dodecylsulfate (SDS), sodium deoxycholate, basic dyes, mitomycin C, and bleomycin, and makes the cell tolerant to the killing action of colicin E1. From lysogens with lambda cI857S7 integrated at a secondary attachment site, a transducing phage (lambda dtolC+) that transduces a tolC recipient to SDS resistance was isolated. A recombinant DNA molecule was constructed in vitro from plasmid pBR322 as a vector, and an EcoRI-BamHI fragment of lambda tolC+ DNA. The resulting plasmid, designated pOK1, was 5.6 megadaltons (Md). The tolC bacteria transformed with plasmid pOK1 restored the TolC+ phenotype with regard to mitomycin C, SDS, and colicin E1 sensitivities. A plasmid with an amber mutation in the tolC gene, designated pOK18, was isolated by the same procedure used for the isolation of pOK1. The plasmid had a molecular weight of 5.6 Md and produced the same size of DNA fragments as the tolC+ plasmid, pOK1, after digestion with the indicated restriction enzymes. The plasmid, pOK18, conferred the TolC+ phenotype when introduced into a tolC strain in the presence of, but not the absence of, an amber suppressor. Plasmid-specified polypeptides were determined by using maxicells of strains uvrA recAsup+ and uvrA recA tyrT, containing each plasmid. Three additional proteins of 54,000 (54K), 29K, and 27K were produced in maxicells containing pOK1. These three proteins were synthesized in maxicells of the uvrA recA tyrT strain carrying pOK18, whereas synthesis of the 54K protein by pOK18 did not take place in maxicells of the uvrA recA sup+ strain, although the other two proteins were produced in normal amounts. From these results we concluded that the product of the tolC gene is a protein with a molecular weight of 54K.

Structured habitats and the evolution of anticompetitor toxins in bacteria

We demonstrate that in liquid cultures, defined in this study as a mass habitat, the outcome of competition between Escherichia coli that produce an antibacterial toxin (colicin) and sensitive E. coli is frequency dependent; the colicinogenic bacteria are at an advantage only when fairly common (frequencies in excess of 2 X 10(-2)). However, we also show that in a soft agar matrix, a structured habitat, the colicinogenic bacteria have an advantage even when initially rare (frequencies as low as 10(-6)). These contrasting outcomes are attributed to the colicinogenic bacteria's lower intrinsic growth rate relative to the sensitive bacteria and the different manner in which bacteria and resources are partitioned in the two types of habitats. Bacteria in a liquid culture exist as randomly distributed individuals and the killing of sensitive bacteria by the colicin augments the amount of resource available to the colicinogenic bacteria to an extent identical to that experienced by the surviving sensitive bacteria. On the other hand, the bacteria in a soft agar matrix exist as single-clone colonies. As the colicinogenic colonies release colicin, they kill neighboring sensitive bacteria and form an inhibition zone around themselves. By this action, they increase the concentration of resources around themselves and overcome their growth rate disadvantage. We suggest that structured habitats are more favorable for the evolution of colicinogenic bacteria.

Temperature-sensitive, colicin M-tolerant mutant of Escherichia coli

A mutant sensitive to colicin M at 30 degrees C and tolerant at 42 degrees C to high concentrations of colicin M was isolated from Escherichia coli K-12. A temperature shift from 30 to 42 degrees C rescued all cells up to the time they started to lyse at 30 degrees C (25 min after addition of colicin M). The growth rate at 42 degrees C remained unaffected by colicin M. AT 42 degrees C the cell-bound colicin M was inactivated by trypsin, sodium dodecyl sulfate, and antiserum against colicin M. Ferrichrome competed with colicin M at 42 degrees C only during the initial adsorption to the common receptor protein in the outer membrane. Since cells lysed earlier at 30 degrees C when they had been preincubated with colicin M at 42 degrees C, we conclude that the process leading finally to cell lysis is initiated at 42 degrees C and stops at a later stage of colicin M trypsin, dodecyl sulfate, and antiserum when cells were transferred from 30 to 42 degrees C, we assume that colicin M is translocated from its target site towards the cell surface. The mutation conferring tolerance was mapped close to the rpsL gene.

Structural and functional properties of colicin M

Colicin M of Escherichia coli Cl139 was isolated in pure form. It consisted of a single polypeptide with a molecular weight of 27,000 +/- 2,000. Colicin M lysed sensitive cells of E. coli but had to act continuously up to the point when lysis commenced (after 20 min). Colicin M was largely resistant to hydrolysis by trypsin except when adsorbed to cells. Within 4 to 5 min after addition of colicin M, cells could be rescued by trypsin or sodium dodecyl sulfate. Later, colicin M was apparently inaccessible to these inactivating agents. Killing of cells by colicin M required Ca2+ ions. Cells could be rescued with ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetate (EGTA) immediately before the onset of lysis. Under these conditions, colicin M remained bound to the cells, and it became again sensitive to trypsin. We conclude that under the influence of EGTA colicin M is removed from its site of action and becomes again accessible to trypsin at the cell surface.

Rifampin and bacteriocin resistance in Bacteroides fragilis

A low-molecular-weight bacteriocin produced by a Bacteroides fragilis strain inhibited ribonucleic acid polymerase activity in crude extracts of a susceptible B. fragilis indicator strain. A total of 10 rifampin-resistant mutants of the indicator strain were isolated. Nine of the rifampin-resistant mutants were resistant to the bacteriocin, and the other mutant was hypersusceptible. The rifampin- and bacteriocin-resistant mutants all adsorbed approximately the same amount of the bacteriocin as the indicator strain. Two of these rifampin- and bacteriocin-resistant mutants were investigated further, and the polymerase activity in crude extracts of the two mutants was not affected by either rifampin or the bacteriocin. The in vitro ribonucleic acid polymerase activity of the hypersusceptible strain was more susceptible to the bacteriocin than the parent indicator strain was. The bacteriocin-producing strain was susceptible to rifampin but was resistant to its own bacteriocin in vivo. The in vitro ribonucleic acid polymerase activity of the producer strain was only slightly affected by 64 arbitrary units of the bacteriocin. Increasing concentrations of the bacteriocin inhibited ribonucleic acid polymerase extracts of the producer strain.

Purification of the viridicin produced by Aerococcus viridans

A new bacteriocin produced by Aerococcus viridans was purified. Bacteria grown on liquid medium synthesized a bacteriocin, viridicin, which can be extracted from the cells by treatment with 0.86 M NaCl solution. Viridicin production was not induced by ultraviolet irradiation or by treatment with mitomycin C. The bacteriocin was purified by ultrafiltration, gel filtration, and preparative polyacrylamide disc gel electrophoresis. The molecular weight was between 100,000 and 120,000. The purified viridicin was homogeneous on polyacrylamide gel electrophoresis. The viridicin was composed of protein, carbohydrate, and lipid.

Colicin E2 is DNA endonuclease

Colicin E2 purified by conventional methods contains a tightly bound low-molecular-weight protein, as has been found with purified colicin E3 [Jakes,N.&Zinder,N.D.(1974) Proc. Natl. Acad. Sci. USA 71, 3380-3384]. Such E2 preparations do not cause DNA cleavage in vitro. After separation from the low-molecular-weight protein, colicin E2 retained the original in vivo killing activity, and in addition showed a high activity in vitro in cleaving various DNA molecules, such as a ColE1 hybrid plasmid and DNAs from Escherichia coli, lambda phage, chiX174 phage, and simian virus 40. The low-molecular-weight protein ("E2-immunity protein") specifically prevented this in vitro DNA cleavage reaction, i.e., had an "immunity function." The results demonstrate that colicin E2 itself is a DNA endonuclease and explain the in vivo effects caused by E2 in sensitive cells as well as the mechanism of immunity in E2-colicinogenic cells.

Bacillus pumilus plasmid pPL10: properties and insertion into Bacillus subtilis 168 by transformation

Bacillus pumilus ATCC 12140 harbors 10 or more copies per chromosome of each two small plasmids. Variants of this strain were isolated which were sensitive to a killing activity produced by the plasmid-containing parent. Each of 24 such sensitive (S) variants tested lacked detectable levels of supercoiled deoxyribonucleic acid. Transduction of S variants to the Kill+ phenotype was performed using phage PBP1 propagated on a mutant of ATCC 12140, designated strain L10, that remained Kill+ but retained only a single plasmid species (plasmid pPL10; molecular weight, approximately 4.4 X 10(6), approximately 20 copies per chromosome; RHO = 1.698). Resulting Kill+ transductants of S variants contained a single plasmid species having a size and copy number comparable to that of pPL10. Transfer of pPL10 from strain L10 TO B. pumilus strain NRS 576 was accomplished by transduction with selection for the Kill+ phenotype. Strain NRS 576 naturally harbors about two copies per chromosome of a 28-million-dalton plasmid, pPL576. In Kill + transductants of NRS 576, plasmids pPL10 and pPL576 stably coexisted at a ratio of about 11 molecules of pPL10 to 1 molecule of pPL576. Therefore, pPL576 and pPL10 are compatible plasmids. B. subtilis 168 is naturally resistant to pPl10- determined killing activity. Plasmid pPl10 was therefore inserted into B-subtilis 168 by transformation, using an indirect selection procedure and a spoB mutant as recipient. The plasmid is stably maintained at an estimated 10 copies per chromosome in the spore- recipient and in spore+ transformants. pPL10 is sensitive to cleavage by the endonucleases Hind III and EcoR1.

Isolation and characterization of T-even ghost-tolerant mutants of Escherichia coli

Mutants of Escherichia coli tolerant to the ghosts of T-even phages (T2, T4, and T6) have been isolated from a strain supersensitive to T6 phage. First, T6 supersensitive mutants were isolated from mutagenized E. coli W2252 by replica plating to T6 phage-overlaid agar. One of them, strain NM101, was mutagenized again, grown, and then plated with a high multiplicity of T4 and T6 ghosts. Surviving cells were checked for tolerance to ghosts and adsorption of phages. One such ghost-tolerant mutant, strain GT29, was tolerant to ghosts of both T4 and T6 phages and sensitive to T2 ghosts. This mutant was also sensitive to ethylenediaminetetraacetic acid and penicillin G and intermediately sensitive to acriflavine, sodium dodecyl sulfate, sodium deoxycholate, actinomycin D, and lysozyme. Another mutant, strain GT62, was tolerant not only to T4 and T6 ghosts but also to T2 ghosts. It was sensitive to sodium dodecyl sulfate, sodium deoxycholate, penicillin G, acridine orange, actinomycin D, phenethyl alcohol, and novobiocin and intermediately sensitive to acriflavine and lysozyme. Spontaneous revertants of strain GT62 were isolated with a frequency of 2.7 X 10(-9). It is suggested that ghosts attack host bacteria indirectly through the cell surface by a mechanism similar to the transmission hypothesis that was originally adopted by Nomura (1967) to explain the mechanism of the action of colicins, and that our ghost-tolerant mutants presumably have defects in the cell surface.

The generation of a ColE1-Apr cloning vehicle which allows detection of inserted DNA

A 3.2 Mdal sequence of DNA, TnA, which contains the ampicillin (Ap) resistance determinant has been translocated from an R plasmid to the plasmid ColE1. A total of 12 isolates were studied. There are at least 8 sites in ColE1 at which TnA has inserted. Insertion at five of these has resulted in a Col-phenotype. One ColE1-Apr plasmid, RSF2124, was examined further and its replication properties are found to be similar to that of the parent plasmid. RSF2124 appears to be a useful plasmid vehicle for the molecular cloning of DNA from diverse prokaryotic sources: it codes for readily detectable Ap resistance and contains a single EcoRI site in a gene affecting colicin biosynthesis so that it is unable to produce colicin upon ligation to other DNA.

Production and properties of an extracellular bacteriocin from Streptococcus mutans bacteriocidal for group A and other streptococci

An extracellular bacteriocidal substance is produced by a serotype c strain of Streptococcus mutans in liquid meduim during the stationary phase of growth. The lethal effect of the substance was demonstrated by the decrease in viable counts of a standardized suspension of group A streptococci in broth. No lysis of affected cells was observed and no changes in appearance of these cells was seen in electron micrographs. The material was effective against certain strains of immmunological groups A, C, D, G, H, L, and O streptococci. It was inactive against strains of S. mutans belonging to the a, b, c, and d serotypes, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The factor was purified 273-fold from the culture fluid by column chromatography. It was sensitive to trysin and Pronase and resistant to catalase. It possessed a molecular weight of more than 20,000 and was not dialyzable. The properties of this substance indicate that it is a bacteriocin. Group A streptococci, which had been treated with antiserum specific for the cell wall group and type antigens, were susceptible to the bacteriocin. Streptococcal strains resistant to the lethal action of the bacteriocin adsorbed the bacteriocin from the solutions, as did the sensitive cells. The bacteriocin was not adsorbed at 0 C.