Physicochemical characterization of phage adsorption toLactobacillus helveticusATCC 15807 cells

Whole Genome Sequence Analysis of Lactiplantibacillus plantarum Bacteriophage P2

Phage P2 was isolated from failed fermentation broth carried out by Lactiplantibacillus plantarum IMAU10120. A previous study in our laboratory showed that this phage belonged to the Siphoviridae family. In this study, this phage's genomic characteristics were analyzed using whole-genome sequencing. It was revealed that phage P2 was 77.9 kb in length and had 39.28% G + C content. Its genome included 96 coding sequences (CDS) and two tRNA genes involved in the function of the structure, DNA replication, packaging, and regulation. Phage P2 had higher host specificity; many tested strains were not infected. Cell wall adsorption experiments showed that the adsorption receptor component of phage P2 might be a part of the cell wall peptidoglycan. This research might enrich the knowledge about genomic information of lactobacillus phages and provide some primary data to establish phage control measures.

Bacteriophage-encoded enzymes destroying bacterial cell membranes and walls, and their potential use as antimicrobial agents

Appearance of pathogenic bacteria resistant to most, if not all, known antibiotics is currently one of the most significant medical problems. Therefore, development of novel antibacterial therapies is crucial for efficient treatment of bacterial infections in the near future. One possible option is to employ enzymes, encoded by bacteriophages, which cause destruction of bacterial cell membranes and walls. Bacteriophages use such enzymes to destroy bacterial host cells at the final stage of their lytic development, in order to ensure effective liberation of progeny virions. Nevertheless, to use such bacteriophage-encoded proteins in medicine and/or biotechnology, it is crucial to understand details of their biological functions and biochemical properties. Therefore, in this review article, we will present and discuss our current knowledge on the processes of bacteriophage-mediated bacterial cell lysis, with special emphasis on enzymes involved in them. Regulation of timing of the lysis is also discussed. Finally, possibilities of the practical use of these enzymes as antibacterial agents will be underlined and perspectives of this aspect will be presented.

Virulence of Leuconostoc phages: Influence of stress conditions associated to dairy processes on their host-phage interactions

In this work, we assessed the impact of technological cell stress conditions, commonly present in industrial dairy processes, on the host strain-phage interactions in Leuconostoc. Adsorption and burst size of LDG (Leuconostoc pseudomesenteroides) and Ln-9 (Leuconostoc mesenteroides) phages were evaluated under the following conditions: i) MRS broth, 30 °C; ii) MRS broth at pH 5.5, 30 °C (acidic stress); iii) MRS broth added of NaCl at 4% w/v, 30 °C (osmotic stress) and iv) MRS broth, 10 °C (cold stress). Experiences were performed with the host strains growing both in MRS broth (30 °C) and under stress conditions. On the other hand, the effect of diverse levels of NaCl, KCl, saccharose and glucose on the adsorption for LDG phage was evaluated. Acidic and cold conditions did not significantly affect the adsorption rates for any phage. However, adsorption rate of phage LDG was highly reduced under osmotic stress (NaCl), except when the host strain previously grew in presence of the salt. LDG phage adsorption was not modified by addition of saccharides, but it drastically decreased in presence of salts. Acidic conditions did not affect the burst size for LDG phage, but Ln-9 phage diminished this parameter (61 phage particles/infected cell). Latency time showed a lengthening of 10 min for both phages, while the burst time remained unaltered for LDG and it was delayed 10 min for Ln-9. LDG phage did not propagate under osmotic conditions, but Ln-9 phage released phage particles with an important increase of its latent period and burst time. No phage particles were released within 90 min after the adsorption step under cold stress. This is the first report about this subject. Under certain conditions of technological stress (osmotic and cold) associated to dairy processes, phage infections on the two systems studied in this work could be delayed/inhibited.

A scaled-down model for the translation of bacteriophage culture to manufacturing scale

Therapeutic bacteriophages are emerging as a potential alternative to antibiotics and synergistic treatment of antimicrobial-resistant infections. This is reflected by their use in an increasing number of recent clinical trials. Many more therapeutic bacteriophage is being investigated in preclinical research and due to the bespoke nature of these products with respect to their limited infection spectrum, translation to the clinic requires combined understanding of the biology underpinning the bioprocess and how this can be optimized and streamlined for efficient methods of scalable manufacture. Bacteriophage research is currently limited to laboratory scale studies ranging from 1-20 ml, emerging therapies include bacteriophage cocktails to increase the spectrum of infectivity and require multiple large-scale bioreactors (up to 50 L) containing different bacteriophage-bacterial host reactions. Scaling bioprocesses from the milliliter scale to multi-liter large-scale bioreactors is challenging in itself, but performing this for individual phage-host bioprocesses to facilitate reliable and robust manufacture of phage cocktails increases the complexity. This study used a full factorial design of experiments approach to explore key process input variables (temperature, time of infection, multiplicity of infection, agitation) for their influence on key process outputs (bacteriophage yield, infection kinetics) for two bacteriophage-bacterial host bioprocesses (T4 - Escherichia coli; Phage K - Staphylococcus aureus). The research aimed to determine common input variables that positively influence output yield and found that the temperature at the point of infection had the greatest influence on bacteriophage yield for both bioprocesses. The study also aimed to develop a scaled down shake-flask model to enable rapid optimization of bacteriophage batch bioprocessing and translate the bioprocess into a scale-up model with a 3 L working volume in stirred tank bioreactors. The optimization performed in the shake flask model achieved a 550-fold increase in bacteriophage yield and these improvements successfully translated to the large-scale cultures.

Changes in Environmental Conditions Modify Infection Kinetics of Dairy Phages

Latent period, burst time, and burst size, kinetic parameters of phage infection characteristic of a given phage/host system, have been measured for a wide variety of lactic acid bacteria. However, most studies to date were conducted in optimal growth conditions of host bacteria and did not consider variations due to changes in external factors. In this work, we determined the effect of temperature, pH, and starvation on kinetic parameters of phages infecting Lactobacillus paracasei, Lactobacillus plantarum, and Leuconostoc mesenteroides. For kinetics assessment, one-step growth curves were carried out in MRS broth at optimal conditions (control), lower temperature, pH 6.0 and 5.0 (MRS₆ and MRS₅, respectively), or in medium lacking carbon (MRS_N) or nitrogen (MRS_C) sources. Phage infection was progressively impaired as environmental conditions were modified from optimal. At lower temperature or pH, infection was delayed, as perceived by longer latent and burst times. Burst size, however, was lower, equal or higher than for controls, but this effect was highly dependent on the particular phage-host system studied. Phage infection was strongly inhibited in MRS_C, but only mildly impaired in MRS_N. Nevertheless, growth of all the bacterial strains tested was severely compromised by starvation, without significant differences between MRS_C and MRS_N, indicating that nitrogen compounds are specifically required for a successful phage infection, beyond their influence on bacterial growth.

Characterization of Two Temperate Lactobacillus paracasei Bacteriophages: Morphology, Kinetics and Adsorption

Background/Aims: Adsorption and kinetic parameters, latent period, burst size and burst time, are characteristics of phage/host systems and can be affected by several environmental factors. As only few studies have focused on temperate dairy phages, we characterized these parameters on temperate Lactobacillus paracasei phages Φ iLp84 and Φ iLp1308, infective for probiotic strains. Methods: Phages were characterized by transmission electron microscopy and genomic DNA restriction. Adsorption under different environmental conditions, phage kinetics and efficiency of plating (EOP) were determined using the double-layer titration method. Results: Phages Φ iLp84 and Φ iLp1308 belong to the Siphoviridae family and have genome sizes of 38 and 34 kbp, respectively. Adsorption was affected by calcium concentration, pH, temperature and host viability, and reached a limit at very high multiplicity of infection. Latency, burst time and burst size were of 85 min, 131 min and 46 for Φ iLp84, and 51 min, 92 min and 28 for Φ iLp1308, respectively, at 37°C. A clear influence of temperature on phage kinetics was observed. Regarding EOP, Φ iLp84 produced plaques on only 1 out of 8 strains tested. Conclusion: Noticeable differences in adsorption, kinetics and EOP were found for two morphologically identical temperate L. paracasei phages of similar origin.

A single-cell analysis of virioplankton adsorption, infection, and intracellular abundance in different bacterioplankton physiologic categories

Culture studies of phage-host systems have shown that phage proliferation strongly depends on the physiological state of the host, but it is still unclear to what extent this holds true within aquatic ecosystems. We used a combination of flow sorting and electron microscopy to explore how the frequency of bacterial cells with attached viruses (FCAV), of visibly infected cells, and the number of intracellular viruses are distributed within five physiologic categories: cells with high (HNA) and low (LNA) nucleic acid content, with a compromised membrane, in division, and with an intact-looking morphology. FCAV was not different between the cellular physiologic categories, suggesting low influence of host physiology on viral adsorption. Infected cells were found within all the physiologic categories, besides the dividing cells, but showed different levels of new virion production, with the abundance of intracellular viruses ranked as follows: HNA > intact-looking cells > LNA > compromised membrane cells. These results favor the physiological control hypothesis of viral progeny production. The calculation of viral production rate of the HNA and LNA cells show that viral infection of HNA cells likely accounts for the majority of viral production. It also show that cells considered as less active can still act as resources for phages, although they contain much less intracellular phage particles.

Isolation and characterisation of a novel Podoviridae-phage infecting Weissella cibaria N 22 from Nham, a Thai fermented pork sausage

A novel Podoviridae lactic acid bacteria (LAB) phage from Nham, a Thai fermented pork sausage, is reported. From a total of 36 samples, 41 isolates of LAB were obtained and employed as hosts for the isolation of phages. From these LAB, only one phage, designated Φ 22, was isolated. The lactic acid bacterial isolate named N 22, sensitive to phage Φ 22 infection was identified by an API 50 CHL kit and N 22's complete sequence of the 16S rDNA sequence. BLASTN analysis of the 16S rDNA sequence revealed a 99% similarity to the 16S rDNA sequence of Weissella cibaria in the GenBank database. Electron micrographs indicated that the phage head was icosahedral with head size and tail length of 92 × 50 nm and 27 nm, respectively. On the basis of the morphology, this phage belongs to the family Podoviridae. Host-range determination revealed that the phage Φ 22 was not capable of infecting the other 40 isolates of LAB and referenced Weissella strains used. A one-step growth experiment showed that the latent period and burst size were estimated at 110 min and 55 phage particles/infected cell, respectively. Furthermore, the phage was infective over a wide range of pH (pH 5.0-8.0) and the D time of Φ 22 was calculated as 88 s at 70 °C and 15s at 80 °C. Phage titers decreased below the detection limit (20 PFU/ml) after heating for more than 60s at 80 °C, or 20s at 90 °C or less than 10s at 100 °C. The results from the study of Nham revealed that Φ 22 was active against the potential starter culture (W. cibaria N 22) for Nham fermentation. Phage infection could adversely affect the fermentation process of Nham by delaying acidification when using W. cibaria N 22 as a starter. However, the results from a sensory test revealed that the panelists did not detect any defects in the final products. This is the first report on the isolation of W. cibaria phage.

Lysogeny in Lactobacillus delbrueckii strains and characterization of two new temperate prolate-headed bacteriophages

AIMS

Frequency of lysogeny in Lactobacillus delbrueckii strains (from commercial and natural starters) and preliminary characterization of temperate bacteriophages isolated from them.

METHODS AND RESULTS

Induction of strains (a total of 16) was made using mitomycin C (MC) (0.5 mug ml(-1)). For 37% of the MC-treated supernatants, it was possible to detect phage particles or presence of killing activity, but only two active bacteriophages were isolated. The two temperate phages isolated were prolate-headed phages which belonged to group c of Lact. delbrueckii bacteriophages classification. Different DNA restriction patterns were obtained for each phage, while the structural protein profiles and packaging sites were identical. Distinctive one-step growth curves were exhibited by each phage. An influence of calcium ions was observed for their lysis in broth but not on the adsorption levels.

CONCLUSIONS

Our study showed that lysogeny is also present in Lact. delbrueckii strains, including commercial strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Commercial strains could be lysogenic and this fact has a great practical importance since they could contribute to the dissemination of active-phage particles in industrial environments.

Argentinean Lactococcus lactis bacteriophages: genetic characterization and adsorption studies

AIMS

Characterization of four virulent Lactococcus lactis phages (CHD, QF9, QF12 and QP4) isolated from whey samples obtained from Argentinean cheese plants.

METHODS AND RESULTS

Phages were characterized by means of electron microscopy, host range and DNA studies. The influence of Ca(2+), physiological cell state, pH and temperature on cell adsorption was also investigated. The double-stranded DNA genomes of these lactococcal phages showed distinctive restriction patterns. Using a multiplex PCR, phage QP4 was classified as a member of the P335 polythetic species while the three others belong to the 936 group. Ca(2+) was not needed for phage adsorption but indispensable to complete cell lysis by phage QF9. The lactococci phages adsorbed normally between pH 5 and pH 8, and from 0 degrees C to 40 degrees C, with the exception of phage QF12 which had an adsorption rate significantly lower at pH 8 and 0 degrees C.

CONCLUSIONS

Lactococcal phages from Argentina belong to the same predominant groups of phages found in other countries and they have the same general characteristics.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work is the first study to characterize Argentinean L. lactis bacteriophages.

Characterization of a new virulent phage (MLC-A) of Lactobacillus paracasei

A new virulent bacteriophage (MLC-A) was recently isolated in Argentina from a probiotic dairy product containing a strain of Lactobacillus paracasei. Observation of the lysate with an electron microscope revealed bacteriophage particles with an icosahedral capsid of 57 +/- 2 nm; with a collar and a noncontractile tail of 156 +/- 3 nm terminating with a baseplate to which a tail fiber was attached. Therefore, phage MLC-A belongs to the Siphoviridae family. This phage was able to survive the pasteurization process and was resistant to alcohols and sodium hypochlorite (400 mg/kg). Only peracetic acid could inactivate high-titer suspensions of phages in a short time. The maximum rates of phage adsorption to its host cells were obtained at 30 degrees C with a pH between 5 and 7, and in the presence of calcium or magnesium ions. The host range of phage MLC-A encompassed L. paracasei and Lactobacillus casei strains, but it was not able to infect Lactobacillus rhamnosus or Lactobacillus gasseri strains. One-step growth kinetics of its lytic development revealed latent and burst periods of 30 and 135 min, respectively, with a burst size of about 69 +/- 4 plaque-forming units per infected cell. Phage MLC-A had a distinctive restriction profile when compared with the 2 well-studied Lactobacillus phages, PL-1 and J-1. The genome size of the MLC-A phage was estimated to be approximately 37 kb. This study presents the description of the first phage specific for L. paracasei isolated in Argentina. The isolation of phage MLC-A indicates that, beside lactic acid bacteria starters, probiotic cultures can also be sensitive to virulent phages in industrial processes.

Phages of Lactobacillus casei/paracasei: response to environmental factors and interaction with collection and commercial strains

AIM

To investigate the influence of several environmental factors on the viability and cell-adsorption for two Lactobacillus casei/paracasei bacteriophages (PL-1 and J-1).

METHODS AND RESULTS

Both phages showed a remarkably high specificity of species, sharing similar host spectra. Two phages and four sensitive strains were used to conform five phage/strain systems. Each showed a particular behaviour (burst size: ranging from 32 to 160 PFU/infective centre; burst time: 120-240 min and latent time: 5-90 min). For both phages, the viability was not significantly affected from pH 4 to 11 (room temperature) and from pH 5 to 10 (37 degrees C). Adsorption rates were not influenced by calcium ions, but decreased after the thermal inactivation of cells. Adsorption rates were high between 0 and 50 degrees C with maximum values at 30 degrees C and pH 6. System PL-1/Lact. paracasei A showed noticeable differences in comparison with the others, being times required to reach 90% of adsorption of 4 h and lower than 45 min, respectively.

CONCLUSIONS

The data obtained in this work demonstrated that environmental parameters can influence the viability and cell adsorption rates of Lact. casei/paracasei phages. The extent of this influence was phage dependent.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work contributes to the enlargement of the currently scarce knowledge of phages of probiotic bacteria.

Characterization of three Lactobacillus delbrueckii subsp. bulgaricus phages and the physicochemical analysis of phage adsorption

AIMS

Three indigenous Lactobacillus delbrueckii subsp. bulgaricus bacteriophages and their adsorption process were characterized.

METHODS AND RESULTS

Phages belonged to Bradley's group B or the Siphoviridae family (morphotype B1). They showed low burst size and short latent periods. A remarkably high sensitivity to pH was also demonstrated. Indigenous phage genomes were linear and double-stranded DNA molecules of approx. 31-34 kbp, with distinctive restriction patterns. Only one phage genome appeared to contain cohesive ends. Calcium ions did not influence phage adsorption, but it was necessary to accelerate cell lysis and improve plaque formation. The adsorption kinetics were similar on viable and nonviable cells, and the adsorption rates were high between 0 and 50 degrees C. SDS and proteinase K treatments did not influence the phage adsorption but mutanolysin and TCA reduced it appreciably. No significant inhibitory effect on phage adsorption was observed for the saccharides tested. This study also revealed the irreversibility of phage adsorption to their hosts.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY

The study increases the knowledge on phages of thermophilic lactic acid bacteria.

Characterization of phage receptors in Streptococcus thermophilus using purified cell walls obtained by a simple protocol

A simple protocol was designed and applied to obtain Streptococcus thermophilus purified cell walls. To identify the structures involved in phage adsorption, the cell walls of two Strep. thermophilus strains were treated with sodium dodecyl sulphate and proteinase K. These treatments did not reduce the adsorption of phages CYM and 0BJ to the cell walls of Strep. thermophilus YSD10 and Strep. thermophilus BJ15, respectively. However, phage binding was reduced when the cell envelopes were treated with mutanolysin or trichloroacetic acid 5%, suggesting that the phage receptor component is part of the peptidoglycan or a polymer closely linked to it. The ability of several saccharides to inactivate both phages was also assayed. These phage inhibition experiments suggested that the phage CYM adsorbed to a component involving glucosamine and rhamnose, while glucosamine and ribose interfered with the adsorption of phage 0BJ.