The potential role of endogenous bacteriophages in controlling invading pathogens

Bacteriophages (phages) are omnipresent in our environment, and recent studies highlight their potential impact on the microbial world. Phages can also be present in mammalian organisms, including man (intestines, oral cavity, urine, sputum and serum). Data are available which suggest that those endogenous phages could play an important role in eliminating bacteria and regulating the body ecosystem. Furthermore, our most recent findings suggest that phages can exert immunosuppressive action in the gut, helping control local inflammatory and autoimmune reactions, and demonstrate anticancer activity. We hypothesize that phages could act in concert with the immune system in immunosurveillance against bacteria, viruses and cancer.

Preventing phage lysis of Lactococcus lactis in cheese production using a neutralizing heavy-chain antibody fragment from llama

Bacteriophage infection is still a persistent problem in large dairy processes despite extensive studies over the last decades. Consequently, new methods are constantly sought to prevent phage infection. In this paper, we show that phage neutralizing heavy-chain antibody fragments, obtained from Camelidae and produced at a large scale in the generally regarded as safe microorganism Saccharomyces cerevisiae, can effectively be used to impede phage induced lysis during a cheese process. The growth inhibition of the cheese starter culture by 10(5) pfu/ml cheese-milk of the small isometric-headed 936-type phage p2 was prevented by the addition of only 0.1 microg/ml (7 nM) of the neutralizing antibody fragment. The use of such antibody fragments in cheese manufacturing are a realistic and interesting option because of the small amount of antibody fragments that are needed. Moreover the antibodies are produced in a food grade microorganism and can easily be isolated from the fermentation liquid in a pure and DNA free form.

Gene organization in a central DNA fragment of Oenococcus oeni bacteriophage fOg44 encoding lytic, integrative and non-essential functions

The nucleotide sequence of a DNA fragment previously shown to contain the attachment site (attP) of Oenococcus oeni phage fOg44 (. Arch. Virol. 143, 523-536) has been determined. Sequence analysis indicated that this 6226bp EcoRI fragment harbours an integrase gene, in the vicinity of a direct repeat rich region defining attP, as well as genes encoding a muramidase-related lysin (Lys) and a holin polypeptide (Hol). Transcriptional studies suggested that lys and hol are mainly co-expressed, late in the lytic cycle, from a promotor located upstream of lys. Between the lytic cassette and the phage integration elements three additional open reading frames were found: orf217 and orf252 of unknown function and orf72, the putative product of which bears 32% identity with acidic excisionases from other Gram positive phages. We have established that the first two orfs, as well as the predicted promotor of orf72, are included in a 2143-bp DNA segment missing from the genome of the deletion mutant fOg44Delta2. Although lysogens of fOg44 and fOg44Delta2 exhibited similar properties, each phage produced two distinguishable types of lysogenic strains, differing in inducibility and immunity to other oenophages.

Lysogenization of Salmonella choleraesuis by phage 14 increases average length of O-antigen chains, serum resistance and intraperitoneal mouse virulence

Three clones from a strain of Salmonella choleraesuis (serogroup C1) were lysogenized with phage 14 (P14) which converts the O-antigen of serogroup C1 salmonellae from O-6,7 to O-6,7,14. The lysogens were compared with their parental non-lysogenic clones with respect to the following properties: average length of O-antigen polysaccharide chains, sensitivity to normal human serum, and mouse-virulence. SDS-polyacrylamide gel electrophoresis of lipopolysaccharides extracted from these bacteria showed that samples from lysogens consisted mainly of long-chained molecules whereas those from non-lysogens contained mainly short-chained molecules. The O-antigen polysaccharide from a lysogen was estimated by chemical analysis to be six times as long as that from a non-lysogen. Lysogens were serum-resistant whereas non-lysogens were serum-sensitive. About 10 times more colony forming units of a lysogen than of a non-lysogen were recovered from the livers and spleens of mice on day 1 and 3 after intraperitoneal inoculation of equal doses. By comparison with S. choleraesuis, lysogenization of S. typhimurium with phage P22 or phage A4 did not affect the chain-length distribution of O-antigen polysaccharide. Our data suggest that phage 14-coded determinants increase efficiency of O-antigen biosynthesis in S. choleraesuis leading to increase in average length of O-polysaccharide chains. Increased serum resistance and mouse virulence are logical consequences of increase in average length of O-polysaccharide chains and represent phage-conferred selective advantage not previously described in Salmonella.

Characterization of the lysogenic repressor (c) gene of the Pseudomonas aeruginosa transposable bacteriophage D3112

Bacteriophage D3112 is a Mu-like temperate transposable phage of Pseudomonas aeruginosa. Genetic mapping and DNA sequence analysis have identified the left end of the phage genome as encoding the transposase enzyme (A) and the lysogenic (c) repressor. The c open reading frame (ORF), located at the leftmost end of the phage genome and transcribed from right to left, has four possible GTG initiation codons. Using site-directed mutagenesis, each of the four GTG codons was modified to GTA, which cannot serve as an initiation codon. Plasmids were constructed expressing either the wild-type repressor ORF or the ORFs containing the mutated GTA codons. When introduced into Pseudomonas aeruginosa, no immunity to superinfection by D3112 was observed when the second GTG had been mutated. Northern blotting analysis demonstrated that the D3112 c repressor is transcribed as a 900-nt mRNA. The promoter region was defined by transcriptional lacZ fusions and primer extension analyses to bp 972-940 from the left end of the phage genome. When the D3112 c repressor was overexpressed and purified as a fusion protein with a C-terminal six-histidine extension (cts15-His6), it showed high affinity for a 261-bp PvuII fragment localized directly upstream of the c repressor ORF. Our results indicate that although D3112 c shows higher amino acid similarity to the lambda family of repressors than it does to those of Mu and D108, it appears that its structure and function more accurately reflect an evolutionary ancestry with those from transposable coliphages Mu and D108.

The primary immunity determinant in modulating the lysogenic immunity of the filamentous bacteriophage cf

Bacteriophage cf is the first single-stranded DNA phage that has been shown to set up a stable lysogenic state with its genome integrated into the host chromosome. From the isolation and characterization of a virulent mutant, cf-tv2, we report the first investigation into the mechanisms of the immunity established by the filamentous bacteriophage. The mutation in cf-tv2 enables the phage to produce plaques on lawns of cf lysogenic cells. The mutation was defined as a 49-nucleotide deletion located in a 0.59 kb NcoI/KpnI fragment of cf replicative form DNA. Two messages, cM1 and cM2, transcribed from the immunity region of wild-type cf but in opposite directions, were detected. In cf-tv2, the 49-nucleotide deletion abolishes cM2 transcription. The primer extension assay suggests a possible RNA-RNA interaction directed by base-pairing of the cM1 and cM2 RNAs. A frameshift mutation of the open reading frame ORF 165, encoded by cM2, resulted in a 10(5) plating efficiency on the cf lysogen. These observations suggest that both RNA-RNA interaction and repressor protein inhibition are involved in the mechanism of cf immunity. A model is proposed for the regulation of cf immunity.

Temperate Bacteriophages-The Powerful Indirect Modulators of Eukaryotic Cells and Immune Functions

Bacteriophages are natural biological entities that limit the growth and amplification of bacteria. They are important stimulators of evolutionary variability in bacteria, and currently are considered a weapon against antibiotic resistance of bacteria. Nevertheless, apart from their antibacterial activity, phages may act as modulators of mammalian immune responses. In this paper, we focus on temperate phages able to execute the lysogenic development, which may shape animal or human immune response by influencing various processes, including phagocytosis of bacterial invaders and immune modulation of mammalian host cells.

[Functional organization of prophage and lysogeny in Erwinia carotovora with participation of a temperate bacteriophage ZF40]

Functional organization of a prophage of the temperate bacteriophage ZF40 of Erwinia carotovora subsp. carotovora which includes its immunity and inducibility as well as its effect on the host phenotype. It was established that the prophage ZF40 forms several different states in E. carotovora which are distinguished by the indices of spontaneous and lysogenic induction. In contrast to other prophages, including the lambdoid ones, the prophage ZF40 is capable to establish cytoplasmic overimmunity which protects the lysogenic system from superinfection by virulent mutants or other homoimmune bacteriophages. An increase of sensitivity of ZF40-lysogens to killing activity of colicino-like carotovoricin (CCTV) and destabilization of defective lysogeny, or resistant MCTV-prophages are related to the phenomenon of the phage lysogenic conversion of E. carotovora.

[The role of the antilysozyme activity of Shigella flexneri as a factor controlling the degree of its resistance to the lytic action of bacteriophages]

The level of the antilysozyme activity of S. flexneri in ensuring the high level of their phage resistance has been studied. The realization of the phage protective effect of antilysozyme activity has been noted to occur due to disturbances in the lysis of infected bacteria by phage-synthetized lysozyme-like enzyme. The direct relationship between the level of the lysozyme production of bacteriophages and their capacity for overcoming the antilysozyme protection of the host bacterium has been shown.