Bacteriophage and their lysins for elimination of infectious bacteria

When phages were originally identified, the possibility of using them as antibacterial agents against pathogens was immediately recognized and put into practise based on the knowledge available at the time. However, with the advent of antibiotics a decline in the use of phage as therapeutics followed. Phages did, however, become more useful in the study of fundamental aspects of molecular biology and in the diagnostic laboratory for the identification of pathogenic bacteria. More recently, the original application of phage as therapeutics to treat human and animal infections has been rekindled, particularly in an era where antibiotic resistance has become so problematic/commonplace. Phage lysins have also been studied and utilized in their own right as potential therapeutics for the treatment of bacterial infections. Indeed the past decade has seen a considerable amount of research worldwide focused on the engineering of phages as antibacterial agents in a wide range of applications. Furthermore, the US Food and Drug Administration and/or the US Department of Agriculture have recently approved commercial phage preparations to prevent bacterial contamination of livestock, food crops, meat and other foods. Such developments have prompted this review into the status of phage research as it pertains to the control of infectious bacteria.     

Gene transfer agents,bacteriophages, and bacteriocins of Rhodopseudomonas capsulata

Thirty-three wild type strains of Rhodopseudomonas capsulata were examined for ability to engage in genetic recombination through mediation by “gene transfer agent” (GTA) particles. The genetic exchange assays were based on capacity of strains to produce or receive GTA required for restoration of photosynthetic growth competence to a non-photosynthetic “white” mutant or for acquisition of resistance to rifampicin. A majority of the strains could either produce or receive GTA, and it was demonstrated that the agent is species specific. Possible relations between GTA and bacteriophages or bacteriocins were investigated. Sixteen types of virulent phages active on Rps. capsulata were isolated and their host ranges determined. Tests for transduction by the phages gave uniformly negative results. The viruses showed strict species specificity, but there was no apparent correlation between capacity of the Rps. capsulata strains to donate or receive GTA and susceptibility to the phages. A comparable survey disclosed that most of the bacterial strains were sensitive to or capable of producing bacteriocins; the latter also appear to be unrelated to GTA activity. The collection of bacterial strains was also screened for detection of lysogenic properties. None of the isolates is a “true” lysogen, but phages were detected in cultures of two strains, which may be “phage carriers” or pseudolysogens.     

Class IIa bacteriocins: biosynthesis, structure and activity

In the last decade, a variety of ribosomally synthesized antimicrobial peptides or bacteriocins produced by lactic acid bacteria have been identified and characterized. As a result of these studies, insight has been gained into fundamental aspects of biology and biochemistry such as producer self protection, membrane-protein interactions, and protein modification and secretion. Moreover, it has become evident that these peptides may be developed into useful antimicrobial additives. Class IIa bacteriocins can be considered as the major subgroup of bacteriocins from lactic acid bacteria, not only because of their large number, but also because of their activities and potential applications. They have first attracted particular attention as listericidal compounds and are now believed to be the next in line if more bacteriocins are to be approved in the future. The present review attempts to provide an insight into general knowledge available for class IIa bacteriocins and discusses common features and recent findings concerning these substances.     

Replicating and non-replicating viral vectors for vaccine development

Viral vectors provide a convenient means to deliver vaccine antigens to select target cells or tissues. A broad spectrum of replicating and non-replicating vectors is available. An appropriate choice for select applications will depend on the biology of the infectious agent targeted, as well as factors such as whether the vaccine is intended to prevent infection or boost immunity in already infected individuals, prior exposure of the target population to the vector, safety, and the number and size of gene inserts needed. Here several viral vectors under development as HIV/AIDS vaccines are reviewed. A vaccine strategy based on initial priming with a replicating vector to enlist the innate immune system, target mucosal inductive sites, and prime both cellular and humoral systemic and mucosal immune responses is proposed. Subsequently, boosting with a replicating or non-replicating vector and/or protein subunits could lead to induction of necessary levels of protective immunity.     

The ecology and evolution of bacteriocins

In this review we focus on the ecological and evolutionary forces that determine the frequency and diversity of colicins inEscherichia coli. To begin, we describe that this killing phenotype is ubiquitous inE. coli, with as many as 50% of the isolates from a population producing colicin toxins, and that each population sampled has its own unique distribution of the more than 20 known colicin types. Next, we explore the dynamics of colicinogeny, which exhibits a typical form of frequency dependence, where the likelihood of successful colicin invasion into a population increases as the initial density of colicinogenic cells increases. We then incorporate thoughts on the evolution of chromosomal resistance to colicins and describe how resistance might influence the dynamics of colicinogen invasion and maintenance and the resulting colicin diversity. The final section deals with a genetic and phylogenetic characterization of colicins and a discussion of the evolutionary mechanisms responsible for generating colicin diversity. In this final section we provide details of the different molecular mechanisms known to play a role in generating colicin diversity, including the two most dominant forces in colincin evolution: recombination and positive, deversifying, selection.     

Gene transfer agents, bacteriophages, and bacteriocins of Rhodopseudomonas capsulata.

Thirty-three wild type strains of Rhodopseudomonas capsulata were examined for ability to engage in genetic recombination through mediation by "gene transfer agent" (GTA) particles. The genetic exchange assays were based on capacity of strains to produce or receive GTA required for restoration of photosynthetic growth competence to a non-photosynthetic "white" mutant or for acquisition of resistance to rifampicin. A majority of the strains could either produce or receive GTA, and it was demonstrated that the agent is species specific. Possible relations between GTA and bacteriophages or bacteriocins were investigated. Sixteen types of virulent phages active on Rps. capsulata were isolated and their host ranges determined. Tests for transduction by the phages gave uniformly negative results. The viruses showed strict species specificity, but there was no apparent correlation between capacity of the Rps. capsulata strains to donate or receive GTA and susceptibility to the phages. A comparable survey disclosed that most of the bacterial strains were sensitive to or capable of producing bacteriocins; the latter also appear to be unrelated to GTA activity. The collection of bacterial strains was also screened for detection of lysogenic properties. None of the isolates is a "true" lysogen, but phages were detected in cultures of two strains, which may be "phage carriers" or pseudolysogens.     

Structure and genetics of circular bacteriocins

Circular bacteriocins are antimicrobial peptides produced by a variety of Gram-positive bacteria. They are part of a growing family of ribosomally synthesized peptides with a head-to-tail cyclization of their backbone that are found in mammals, plants, fungi and bacteria and are exceptionally stable. These bacteriocins permeabilize the membrane of sensitive bacteria, causing loss of ions and dissipation of the membrane potential. Most circular bacteriocins probably adopt a common 3D structure consisting of four or five α-helices encompassing a hydrophobic core. This review compares the various structures, as well as the gene clusters that encode circular bacteriocins, and discusses the biogenesis of this unique class of bacteriocins.     

Production, recovery and purification of bacteriocins from lactic acid bacteria

Bacteriocins produced by lactic acid bacteria are a heterogeneous group of peptide inhibitors which include lantibiotics (class I, e.g. nisin), small heat-stable peptides (class II, e.g. pediocin AcH/PA1) and large heat-labile proteins (class III, e.g. helveticin J). Many bacteriocins belonging to the first two groups can be successfully used to inhibit undesirable microorganisms in foods, but only nisin is produced industrially and is licensed for use as a food preservative in a partially purified form. This review focuses on the production and purification of class I and class II bacteriocins from lactic acid bacteria. Bacteriocin production is growth associated but the yield of bacteriocin per unit biomass is affected by several factors, including the producing strain, media (carbohydrate and nitrogen sources, cations, etc.) and fermentation conditions (pH, temperature, agitation, aeration and dilution rate in continuous fermentations). Continuous fermentation processes with cell recycle or immobilized cells can result in a dramatic improvement in productivity over batch fermentations. Several simple recovery processes, based on adsorbing bacteriocin on resins or silica compounds, have been developed and can be used to build integrated production processes. Received: 29 December 1998 / Received revision: 23 April 1999 / Accepted: 23 April 1999     

The permeability of human cells to cations after treatment with resorcinol,n-butyl alcohol,and similar lysins

The form of families of curves relating K loss to time in systems containing hypolytic concentrations of resorcinol and of n-butyl alcohol points to the human red cell's being slightly permeable to K and Na even when it is in isotonic NaCl (or plasma), and to the effect of the hypolytic concentrations of lysin being such as to increase this permeability. The rate of reentry of K into red cells which have lost it is more rapid than the rate of the previous loss. This may be due to the reimmersion of the lysin-treated cells in isotonic KCl producing further modifications of the ion-restricting mechanisms associated with the red cell structure. The volume changes observed in systems which show the large K-Na exchanges produced by resorcinol and by n-butyl alcohol are not the same as those which would be expected on the basis of the dual mechanism of hemolysis hypothesis or of the colloid-osmotic hemolysis hypothesis. Extensive swelling of the red cells occurs only when the concentrations of lysin are large enough to produce considerable hemolysis.     

Agglutinins and lysins in the molluscan family Planorbidae: a survey of hemolymph, egg-masses, and albumen-gland extracts

1. Thirty-one strains representing eight species and four genera of the molluscan family Planorbidae were surveyed for the presence of hemagglutinins and hemolysins. Extracts prepared from albumen-glands and egg-masses, as well as hemolymph, were assayed by a micro-hemagglutination technique in which human erythrocytes were used as receptors. 2. Hemagglutinins and hemolysins for human erythrocytes were not uniformly present in all members of the family and detection of these substances depended, in part, on the material tested. 3. Neither heating to 56 degrees C, dialysis, storage at -20 degrees C for up to a year, nor repeated freezing and thawing appeared to effect the agglutinating activity of egg or albumen-gland extracts. 4. Inhibition of the agglutinating activity of Helisoma hemolymph could be accomplished with N-Acetyl-D-Galactosamine, but this sugar had no effect on the activity of Biomphalaria agglutinins. 5. There is evidence to suggest that the source and nature of agglutinins from Helisoma and Biomphalaria species are different. 6. Lectins may be of some value in characterizing snail populations and as an aid in the taxonomic discrimination of species.     

Discovering the bacterial circular proteins: bacteriocins, cyanobactins, and pilins

Over recent years, several examples of natural ribosomally synthesized circular proteins and peptides from diverse organisms have been described. They are a group of proteins for which the precursors must be post-translationally modified to join the N and C termini with a peptide bond. This feature appears to confer a range of potential advantages because these proteins show increased resistance to proteases and higher thermodynamic stability, both of which improve their biological activity. They are produced by prokaryotic and eukaryotic organisms and show diverse biological activities, related mostly to a self-defense or competition mechanism of the producer organisms, with the only exception being the circular pilins. This minireview highlights ribosomally synthesized circular proteins produced by members of the domain Bacteria: circular bacteriocins, cyanobactins, and circular pilins. We pay special attention to the genetic organization of the biosynthetic machinery of these molecules, the role of circularization, and the differences in the possible circularization mechanisms.     

The lysins of bacteriophages infecting lactic acid bacteria

This short review highlights the complete absence of literature on lysins of bacteriophages infecting species like S. salivarius subsp. thermophilus, Pediococcus and Leuconostoc species, L. helveticus, L. acidophilus, L. plantarum and L. brevis, which are also widely used in the dairy industry. The lysins described share some similar biochemical characteristics: optimal pH and temperature, site of hydrolysis inside the peptidoglycan, and some activators and inhibitors. The cloning of the genes encoding these lysins only began in the last few years and four of them have been completely sequenced. In the future, these lysin genes could be interestingly compared to the host autolysin(s) gene(s). By contrast, the passage of phage lysins through the cytoplasmic membrane of the host cell in order to reach the peptidoglycan (via a signal sequence or the presence of a holin) seems not to be clearly resolved. The presence of a second open-reading frame upstream from the gene of the lysin, enabling a putative holin to be encoded, has already been suggested. No doubt our ever increasing knowledge about bacteriophage genome organization will help to elucidate this question. Meanwhile the obtention of a Lactococcus strain with an autolytic phenotype, using a bacteriophage lysin gene, as well as the successful use of purified PL1 lysin to obtain protoplasts of L. casei encourage us to continue to explore the field of bacteriophage lysins.