Bacteriophages of the genus Lactobacillus

Characterization of Lactobacillus bulgaricus Bacteriophage ch2

Bacteriophage ch2, a virulent bacteriophage of Lactobacillus bulgaricus CH2, was characterized according to its morphology, genome size, structural proteins, and growth kinetics. Electron micrographs revealed that bacteriophage ch2 has an icosahedral head of 50-nm diameter and a long tail of 170 nm. Its genome is linear and 35 kilobases in length, and its structural proteins consist of two major and eight minor proteins. One-step growth kinetics of bacteriophage ch2 under optimal conditions (45 degrees C in MRS medium [Oxoid Ltd.]) showed that the latent time was 40 min, the rise period was 15 min, and the burst size was 130 bacteriophages per cell. To monitor the effects of bacteriophage infection on host growth and beta-galactosidase production, the absorbance of the culture and the beta-galactosidase activity were followed during the infection cycle. Before lysis the infected culture continued to grow and produce beta-galactosidase at the same rate as the uninfected culture.

Inactivation of Lactobacillus bacteriophage PL-1 by microwave irradiation

The effect of microwave irradiation on the survival of bacteriophage PL-1, which is specific for Lactobacillus casei, was studied using a commercial 2,450 MHz microwave oven. The phages were inactivated by microwave irradiation according to almost first-order reaction kinetics. The rate of phage inactivation was not affected by the difference in the continuous or intermittent irradiation, nor by the concentrations of phages used, but was affected by the volume of phage suspensions, which prevented the loss of generated heat. Microwave irradiation of phage suspensions produced a number of ghost phages with empty heads, but fragmentation of the tail was hardly noticed. The breakage of phage genome DNA was primarily caused by the heat generated by microwave irradiation, whereas the phage DNA was not affected by the same temperature achieved by heat from outside. Thus we concluded that the phage-inactivating effect of microwave irradiation was mainly attributed to a thermal microwave effect, which was much stronger than a simple thermal exposure.

Cloning, sequence and in vitro transcription/translation analysis of a 3.2-kb EcoRI-HindIII fragment of Leuconostoc oenos bacteriophage L10

A 3.2-kb EcoRI-HindIII DNA fragment of Leuconostoc oenos bacteriophage L10 was cloned and sequenced. Computer-assisted analysis of the sequence identified eleven possible open reading frames (ORFs) that were all on the same strand. In vitro transcription/translation analysis of the full-length DNA fragment yielded five prominent proteins that were correlated with ORFs by their sizes and expression from deleted clones. Only those ORFs containing recognizable Shine-Dalgarno sequences coded for proteins. Neither the nucleotide sequence, nor deduced amino-acid sequences showed significant homology with other known sequences.

Comparative Study of 35 Bacteriophages of Lactobacillus helveticus: Morphology and Host Range

This survey included 23 phages isolated from cheese whey and 12 temperate phages induced with mitomycin from their lysogenic host strains. All of the phages had an isometric head and a tail with a contractile sheath. In addition, short-tailed (160-nm-long) and long-tailed (260-nm-long) phages were distinguished. Short-tailed phages were by far the most widespread in French cheese factories (32 of the 35 phages studied). The study of phage relationships enabled two large groups of strains to be distinguished: those not or slightly sensitive to phages and those very sensitive to phages. There was an obvious relationship in the first group between phage sensitivity (or resistance) and the geographic origin of the strains. The second group contained primarily strains from large international collections and those isolated from commercial starters. The relationships among short-tailed phages, either temperate or isolated as lytic, suggest that lysogenic strains could be the major source of phages in French cheese factories.

Electron microscope studies on the intracellular growth of PL-1 phage of Lactobacillus casei

Ultrathin sections of the cells of Lactobacillus casei infected with or without PL-1 phages were observed by the rapid-freezing and substitution-fixation method. Phage-head-like particles were first observed in the nuclear region. The region was seen more widely dispersed in the cytoplasm than that observed by the conventional chemical fixation method. The features of cells just broken open by the infected phages were observed by the sedimentation method devised by us. The bursting occurred in more than one place in the cells with liberation of progeny phages.

Characterization of the temperate bacteriophage phi adh and plasmid transduction in Lactobacillus acidophilus ADH

Lactobacillus acidophilus ADH is lysogenic and harbors an inducible prophage, phi adh. Bacteriophage were detected in cell lysates induced by treatment with mitomycin C or UV light. Electron microscopy of lysates revealed phage particles with a hexagonal head (62 nm) and a long, noncontractile, flexible tail (398 nm) ending in at last five short fibers. Phage phi adh was classified within Bradley's B1 phage group and the Siphoviridae family. The phi adh genome is a linear double-stranded DNA molecule of 41.7 kilobase pairs with cohesive ends: a physical map of the phi adh genome was constructed. A prophage-cured derivative of strain ADH, designated NCK102, was isolated from cells that survived UV exposure. NCK102 did not exhibit mitomycin C-induced lysis, but broth cultures lysed upon addition of phage. Phage phi adh produced clear plaques on NCK102 in media containing 10 mM CaCl2 at pH values between 5.2 and 5.5. A relysogenized derivative (NCK103) of NCK102 was isolated that exhibited mitomycin C-induced lysis and superinfection immunity to phage phi adh. Hybridization experiments showed that the phi adh genome was present in the ADH and NCK103 chromosomes, but absent in NCK102. These results demonstrated classic lytic and lysogenic cycles of replication for the temperate phage phi adh induced from L. acidophilus ADH. Phage phi adh also mediates transduction of plasmid DNA. Transductants of strain ADH containing pC194, pGK12, pGB354, and pVA797 were detected at frequencies in the range of 3.6 x 10(-8) to 8.3 x 10(-10) per PFU. Rearrangements or deletions were not detected in these plasmids as a consequence of transduction. This is the first description of plasmid transduction in the genus Lactobacillus.

Genetic transfer systems for delivery of plasmid deoxyribonucleic acid to Lactobacillus acidophilus ADH: conjugation, electroporation, and transduction

Lactobacillus acidophilus ADH is a bacteriocin-producing human isolate that adheres to human fetal intestinal cells and human ileal cells. We have employed both electroporation and conjugation methodologies to transfer various plasmids to L. acidophilus ADH. Furthermore, we have demonstrated transduction of plasmid DNA within this strain by a temperate bacteriophage (phi adh) harbored by L. acidophilus ADH. Plasmid pGK12 was introduced into strain ADH by electroporation at frequencies as high as 3.3 X 10(5) transformants/micrograms of plasmid DNA. Transconjugants of strain ADH were recovered at frequencies of 10(-2) (pAMB1), 10(-4) (pVA797::Tn917), and 10(-4) (pVA797) per donor cell after filter-mating with Lactococcus lactis ssp. lactis. Plasmid pGK12 was transduced from a phage phi adh lysogen into a recipient strain of L. acidophilus ADH at an average frequency of 3.4 X 10(-8) transductants/pfu. Transformants, transconjugants, or transductants were verified by both phenotype and plasmid profile for acquisition of plasmid DNA. The ability to transfer plasmids and mobilize DNA sequences by electroporation, conjugation, and transduction will augment our efforts to define and characterize the activities of L. acidophilus in the intestinal tract.

Bacteriophages of lactobacilli

Lactobacilli are members of the bacterial flora of lactic starter cultures used to generate lactic acid fermentation in a number of animal or plant products used as human or animals foods. They can be affected by phage outbreaks, which can result in faulty and depreciated products. Two groups of phages specific of Lactobacillus casei have been thoroughly studied. 1. The first group is represented by phage PL-1. This phage behaves as lytic in its usual host L. casei ATCC 27092, but can lysogenize another strain, L. casei ATCC 334. Bacterial receptors of this phage are located in a cell-wall polysaccharide and rhamnose is the main component of the receptors. Ca2+ and adenosine triphosphate (ATP) are indispensable to ensure the injection of the phage DNA into the bacterial cell. The phage DNA is double-stranded, mostly linear, but with cohesive ends which enables it to be circularized. The vegetative growth of PL-1 proceeds according to the classical mode. Cell lysis is produced by an N-acetyl-muramidase at the end of vegetative growth. 2. The second group is represented by the temperate phage phi FSW of L. casei ATCC27139. It has been shown how virulent phages originate from this temperate phage in Japanese dairy plants. The lysogenic state of phi FSW can be altered either by point mutations or by the insertion of a mobile genetic element called ISL 1, which comes from the bacterial chromosome. This is the first transposable element that has been described in lactobacilli. Lysogeny appears to be widespread among lactobacilli since one study showed that 27% of 148 strains studied, representing 15 species, produced phage particles after induction by mitomycin C. Similarly, 23 out of 30 strains of Lactobacillus salivarius are lysogenic and produce, after induction by mitomycin C, temperate phages, killer particles, or defective phages. Temperate phages have also been found in 10 out of 105 strains of Lactobacillus bulgaricus or Lactobacillus lactis after induction by mitomycin C. Phages so far studied of the latter 2 and closely related lactobacilli, either temperate or isolated as lytic, may be divided into 4 unrelated groups called a, b, c and d. Most of these phages are found in group a and an unquestionable relationship has already been shown between lytic phages and temperate phages that belong to this group. Lytic phage LL-H of L. lactis LL 23, isolated in Finland, is one of the most representative of those of group a and has been extensively studied on the molecular level.

Thirteen Virulent and Temperate Bacteriophages of Lactobacillus bulgaricus and Lactobacillus lactis Belong to a Single DNA Homology Group

Thirteen virulent phages and two temperate phages of two closely related bacterial species ( Lactobacillus lactis and L. bulgaricus ) were compared for their protein composition, their antigenic properties, their restriction endonuclease patterns, and their DNA homology. The immunoblotting studies and the DNA-DNA hybridizations showed that the phages could be differentiated into two groups. One group contained 2 temperate phages of L. bulgaricus and 11 virulent phages of L. lactis. Inside each group, at least two common proteins of identical sizes could be detected for each phage. These proteins were able to cross-react in immunoblotting experiments with an antiserum raised against one phage of the same group. Temperate phage DNAs showed partial homology with DNAs from some virulent phages. These homologies seem to be located on the region coding for the structural proteins since recombinant plasmids coding for one of the major phage proteins of one phage were able to hybridize with the DNAs from phages of the same group. These results suggest that temperate and virulent phages may be related to one another.

Physical and genetic characterization of the genome of Lactobacillus lactis bacteriophage LL-H

Bacteriophage LL-H is a virulent phage of Lactobacillus lactis LL23. A restriction map of the phage genome was constructed with various restriction endonucleases. This chromosome has a 34-kilobase size and seems to be circularly permuted. We used a bank of LL-H restriction fragments to study the expression of five of the seven main phage particle proteins. Immunoblotting experiments permitted the mapping on the chromosome of several genes coding for phage particle proteins. We also show that the gene of the main capsid protein is expressed from its own promoter in an Escherichia coli strain.

The bacteriophages of lactic acid bacteria with emphasis on genetic aspects of group N lactic streptococci

The paper reviews the bacteriophages of the group N lactic streptococci centering on isolation, ultrastructure and morphology, phage receptors, the structure of the genome, protein components, the phenomenon of the lysogenic state, restriction-modification systems and genetic exchange by transfection and transduction. The resulting consequences on industrial fermentations are briefly discussed.