In the billion years that bacteriophage (or phage) have existed together with bacteria the phage have evolved systems that may be exploited for our benefit. One of these is the lytic system used by the phage to release their progeny from an infected bacterium. Endolysins (or lysins) are highly evolved enzymes in the lytic system produced to cleave essential bonds in the bacterial cell wall peptidoglycan for progeny release. Small quantities of purified recombinant lysin added externally to gram-positive bacteria results in immediate lysis causing log-fold death of the target bacterium. Lysins have now been used successfully in a variety of animal models to control pathogenic antibiotic resistant bacteria found on mucosal surfaces and in infected tissues. The advantages over antibiotics are their specificity for the pathogen without disturbing the normal flora, the low chance of bacterial resistance, and their ability to kill colonizing pathogens on mucosal surfaces, a capacity previously unavailable. Lysins therefore, may be a much-needed anti-infective (or enzybiotic) in an age of mounting antibiotic resistance.
bacteriophage; endolysin; gram-positive bacteria; lytic enzymes; mucosal colonization; phage; prophylaxis; therapeutic
Peptidoglycan lytic enzymes (endolysins) induce bacterial host cell lysis in the late phase of the lytic bacteriophage replication cycle. Endolysins OBPgp279 (from Pseudomonas fluorescens phage OBP), PVP-SE1gp146 (Salmonella enterica serovar Enteritidis phage PVP-SE1) and 201ϕ2-1gp229 (Pseudomonas chlororaphis phage 201ϕ2-1) all possess a modular structure with an N-terminal cell wall binding domain and a C-terminal catalytic domain, a unique property for endolysins with a Gram-negative background. All three modular endolysins showed strong muralytic activity on the peptidoglycan of a broad range of Gram-negative bacteria, partly due to the presence of the cell wall binding domain. In the case of PVP-SE1gp146, this domain shows a binding affinity for Salmonella peptidoglycan that falls within the range of typical cell adhesion molecules (Kaff = 1.26×106 M−1). Remarkably, PVP-SE1gp146 turns out to be thermoresistant up to temperatures of 90°C, making it a potential candidate as antibacterial component in hurdle technology for food preservation. OBPgp279, on the other hand, is suggested to intrinsically destabilize the outer membrane of Pseudomonas species, thereby gaining access to their peptidoglycan and exerts an antibacterial activity of 1 logarithmic unit reduction. Addition of 0.5 mM EDTA significantly increases the antibacterial activity of the three modular endolysins up to 2–3 logarithmic units reduction. This research work offers perspectives towards elucidation of the structural differences explaining the unique biochemical and antibacterial properties of OBPgp279, PVP-SE1gp146 and 201ϕ2-1gp229. Furthermore, these endolysins extensively enlarge the pool of potential antibacterial compounds used against multi-drug resistant Gram-negative bacterial infections.
Endolysins (or lysins) are highly evolved enzymes produced by bacteriophage (phage for short) to digest the bacterial cell wall for phage progeny release. In Gram-positive bacteria, small quantities of purified recombinant lysin added externally results in immediate lysis causing log-fold death of the target bacterium. Lysins have been used successfully in a variety of animal models to control pathogenic antibiotic-resistant bacteria found on mucosal surfaces and infected tissues. Their specificity for the pathogen without disturbing the normal flora, the low chance of bacterial resistance, and their ability to kill colonizing pathogens on mucosal surfaces, a capacity previously unavailable, make them ideal anti-infectives in an age of mounting resistance. Here we review the current literature showing the effectiveness of these enzymes in controlling a variety of infections.
Phage; Bacteriophage; Cell wall; Gram-positive bacteria; Infection; Lysin
Bacillus cereus is a foodborne pathogen that causes emetic or diarrheal types of food poisoning. The incidence of B. cereus food poisoning has been gradually increasing over the past few years, therefore, biocontrol agents effective against B. cereus need to be developed. Endolysins are phage-encoded bacterial peptidoglycan hydrolases and have received considerable attention as promising antibacterial agents.
The endolysin from B. cereus phage B4, designated LysB4, was identified and characterized. In silico analysis revealed that this endolysin had the VanY domain at the N terminus as the catalytic domain, and the SH3_5 domain at the C terminus that appears to be the cell wall binding domain. Biochemical characterization of LysB4 enzymatic activity showed that it had optimal peptidoglycan hydrolase activity at pH 8.0-10.0 and 50°C. The lytic activity was dependent on divalent metal ions, especially Zn2+. The antimicrobial spectrum was relatively broad because LysB4 lysed Gram-positive bacteria such as B. cereus, Bacillus subtilis and Listeria monocytogenes and some Gram-negative bacteria when treated with EDTA. LC-MS analysis of the cell wall cleavage products showed that LysB4 was an L-alanoyl-D-glutamate endopeptidase, making LysB4 the first characterized endopeptidase of this type to target B. cereus.
LysB4 is believed to be the first reported L-alanoyl-D-glutamate endopeptidase from B. cereus-infecting bacteriophages. The properties of LysB4 showed that this endolysin has strong lytic activity against a broad range of pathogenic bacteria, which makes LysB4 a good candidate as a biocontrol agent against B. cereus and other pathogenic bacteria.
Lysins are highly evolved enzymes produced by bacteriophage ( phage for short) to digest the bacterial cell wall for phage progeny release. In gram-positive bacteria, small quantities of purified recombinant lysin added externally results in immediate lysis causing log-fold death of the target bacterium. Lysins have been used successfully in a variety of animal models to control pathogenic antibiotic resistant bacteria found on mucosal surfaces and infected tissues. The advantages over antibiotics are their specificity for the pathogen without disturbing the normal flora, the low chance of bacterial resistance to lysins, and their ability to kill colonizing pathogens on mucosal surfaces, a capacity previously unavailable. Thus, lysins may be a much needed anti-infective in an age of mounting antibiotic resistance.
Phage; Bacteriophage; Cell wall; Gram-positive bacteria; Infection; Lysin; Lytic enzymes; Mucosal colonization; Pathogens; Peptidoglycan
Bacteriophage endolysins (lysins) bind to a cell wall substrate and cleave peptidoglycan, resulting in hypotonic lysis of the phage-infected bacteria. When purified lysins are added externally to Gram-positive bacteria they mediate rapid death by the same mechanism. For this reason, novel therapeutic strategies have been developed using such enzybiotics. However, like other proteins introduced into mammalian organisms, they are quickly cleared from systemic circulation. PEGylation has been used successfully to increase the in vivo half-life of many biological molecules and was therefore applied to Cpl-1, a lysin specific for S. pneumoniae. Cysteine-specific PEGylation with either PEG 10K or 40K was achieved on Cpl-1 mutants, each containing an additional cysteine residue at different locations To the best of our knowledge, this is the first report of the PEGylation of bacteriophage lysin. Compared to the native enzyme, none of the PEGylated conjugates retained significant in vitro anti-pneumococcal lytic activity that would have justified further in vivo studies. Since the anti-microbial activity of the mutant enzymes used in this study was not affected by the introduction of the cysteine residue, our results implied that the presence of the PEG molecule was responsible for the inhibition. As most endolysins exhibit a similar modular structure, we believe that our work emphasizes the inability to improve the in vivo half-life of this class of enzybiotics using a cysteine-specific PEGylation strategy.
Bacteriophage; S. pneumoniae; Cpl-1; PEGylation; Endolysin; Enzybiotic
Mycobacteriophages are dsDNA viruses that infect mycobacterial hosts. The mycobacteriophage Ms6 accomplishes lysis by producing two cell wall hydrolytic enzymes, Lysin A (LysA) that possesses a central peptidoglycan recognition protein (PGRP) super-family conserved domain with the amidase catalytic site, that cleaves the amide bond between the N-acetylmuramic acid and L-alanine residues in the oligopeptide crosslinking chains of the peptidoglycan and Lysin B (LysB) a mycolylarabinogalactan esterase that hydrolyzes the mycolic acids from the mycolyl-arabinogalactan-peptidoglycan complex. Examination of the endolysin (lysA) DNA sequence revealed the existence of an embedded gene (lysA241) encoded in the same reading frame and preceded by a consensus ribosome-binding site. In the present work we show that, even though lysA is essential for Ms6 viability, phage mutants that express only the longer (Lysin384) or the shorter (Lysin241) endolysin are viable, but defective in the normal timing, progression and completion of host cell lysis. In addition, both endolysins have peptidoglycan hydrolase activity and demonstrated broad growth inhibition activity against various Gram-positive bacteria and mycobacteria.
Interest in phage therapy has grown over the past decade due to the rapid emergence of antibiotic resistance in bacterial pathogens. However, the use of bacteriophages for therapeutic purposes has raised concerns over the potential for immune response, rapid toxin release by the lytic action of phages, and difficulty in dose determination in clinical situations. A phage that kills the target cell but is incapable of host cell lysis would alleviate these concerns without compromising efficacy.
We developed a recombinant lysis-deficient Staphylococcus aureus phage P954, in which the endolysin gene was rendered nonfunctional by insertional inactivation. P954, a temperate phage, was lysogenized in S. aureus strain RN4220. The native endolysin gene on the prophage was replaced with an endolysin gene disrupted by the chloramphenicol acetyl transferase (cat) gene through homologous recombination using a plasmid construct. Lysogens carrying the recombinant phage were detected by growth in presence of chloramphenicol. Induction of the recombinant prophage did not result in host cell lysis, and the phage progeny were released by cell lysis with glass beads. The recombinant phage retained the endolysin-deficient genotype and formed plaques only when endolysin was supplemented. The host range of the recombinant phage was the same as that of the parent phage. To test the in vivo efficacy of the recombinant endolysin-deficient phage, immunocompromised mice were challenged with pathogenic S. aureus at a dose that results in 80% mortality (LD80). Treatment with the endolysin-deficient phage rescued mice from the fatal S. aureus infection.
A recombinant endolysin-deficient staphylococcal phage has been developed that is lethal to methicillin-resistant S. aureus without causing bacterial cell lysis. The phage was able to multiply in lytic mode utilizing a heterologous endolysin expressed from a plasmid in the propagation host. The recombinant phage effectively rescued mice from fatal S. aureus infection. To our knowledge this is the first report of a lysis-deficient staphylococcal phage.
Staphylococcus aureus is a food-borne pathogen and the most common cause of infections in hospitalized patients. The increase in the resistance of this pathogen to antibacterials has made necessary the development of new anti-staphylococcal agents. In this context, bacteriophage lytic enzymes such as endolysins and structural peptidoglycan (PG) hydrolases have received considerable attention as possible antimicrobials against gram-positive bacteria.
S. aureus bacteriophage vB_SauS-phiIPLA88 (phiIPLA88) contains a virion-associated muralytic enzyme (HydH5) encoded by orf58, which is located in the morphogenetic module. Comparative bioinformatic analysis revealed that HydH5 significantly resembled other peptidoglycan hydrolases encoded by staphylococcal phages. The protein consists of 634 amino acid residues. Two putative lytic domains were identified: an N-terminal CHAP (cysteine, histidine-dependent amidohydrolase/peptidase) domain (135 amino acid residues), and a C-terminal LYZ2 (lysozyme subfamily 2) domain (147 amino acid residues). These domains were also found when a predicted three-dimensional structure of HydH5 was made which provided the basis for deletion analysis. The complete HydH5 protein and truncated proteins containing only each catalytic domain were overproduced in E. coli and purified from inclusion bodies by subsequent refolding. Truncated and full-length HydH5 proteins were all able to bind and lyse S. aureus Sa9 cells as shown by binding assays, zymogram analyses and CFU reduction analysis. HydH5 demonstrated high antibiotic activity against early exponential cells, at 45°C and in the absence of divalent cations (Ca2+, Mg2+, Mn2+). Thermostability assays showed that HydH5 retained 72% of its activity after 5 min at 100°C.
The virion-associated PG hydrolase HydH5 has lytic activity against S. aureus, which makes it attractive as antimicrobial for food biopreservation and anti-staphylococcal therapy.
Bacteriophage endolysins are peptidoglycan hydrolases employed by the virus to lyse the host at the end of its multiplication phase. They have found many uses in biotechnology; not only as antimicrobials, but also for the development of novel diagnostic tools for rapid detection of pathogenic bacteria. These enzymes generally show a modular organization, consisting of N‐terminal enzymatically active domains (EADs) and C‐terminal cell wall‐binding domains (CBDs) which specifically target the enzymes to their substrate in the bacterial cell envelope. In this work, we used individual functional modules of Listeria phage endolysins to create fusion proteins with novel and optimized properties for labelling and lysis of Listeria cells. Chimaeras consisting of individual EAD and CBD modules from PlyPSA and Ply118 endolysins with different binding specificity and catalytic activity showed swapped properties. EAD118–CBDPSA fusion proteins exhibited up to threefold higher lytic activity than the parental endolysins. Recombineering different CBD domains targeting various Listeria cell surfaces into novel heterologous tandem proteins provided them with extended recognition and binding properties, as demonstrated by fluorescent GFP‐tagged CBD fusions. It was also possible to combine the binding specificities of different single CBDs in heterologous tandem CBD constructs such as CBD500‐P35 and CBDP35‐500, which were then able to recognize the majority of Listeria strains. Duplication of CBD500 increased the equilibrium cell wall binding affinity by approximately 50‐fold, and the enzyme featuring tandem CBD modules showed increased activity at higher ionic strength. Our results demonstrate that modular engineering of endolysins is a powerful approach for the rational design and optimization of desired functional properties of these proteins.
With their ability to lyse Gram-positive bacteria, phage lytic enzymes (or lysins) have received a great deal of attention as novel anti-infective agents. The number of known genes encoding these peptidoglycan hydrolases has increased markedly in recent years, due in large part to advances in DNA sequencing technology. As the genomes of more and more bacterial species/strains are sequenced, lysin-encoding open reading frames (ORFs) can be readily identified in lysogenized prophage regions. In the current study, we sought to assess lysin diversity for the medically relevant pathogen Clostridium perfringens. The sequenced genomes of nine C. perfringens strains were computationally mined for prophage lysins and lysin-like ORFs, revealing several dozen proteins of various enzymatic classes. Of these lysins, a muramidase from strain ATCC 13124 (termed PlyCM) was chosen for recombinant analysis based on its dissimilarity to previously characterized C. perfringens lysins. Following expression and purification, various biochemical properties of PlyCM were determined in vitro, including pH/salt-dependence and temperature stability. The enzyme exhibited activity at low µg/ml concentrations, a typical value for phage lysins. It was active against 23 of 24 strains of C. perfringens tested, with virtually no activity against other clostridial or nonclostridial species. Overall, PlyCM shows potential for development as an enzybiotic agent, demonstrating how expanding genomic databases can serve as rich pools for biotechnologically relevant proteins.
Lysin; Prophage; Enzybiotic; Muramidase; Clostridium perfringens
Group B streptococci (GBS) are the leading cause of neonatal meningitis and sepsis worldwide. The current treatment strategy is limited to intrapartum antibiotic prophylaxis in pregnant women to prevent early-onset neonatal diseases, but considering the potential for antibiotic resistance, the risk of losing control over the disease is high. To approach this problem, we have developed a bacteriophage (phage) lytic enzyme to remove colonizing GBS. Bacteriophage muralytic enzymes, termed lysins, are highly evolved molecules designed to degrade the cell wall of host bacteria to release phage particles from the bacterial cytoplasm. Several different lysins have been developed to specifically kill bacterial pathogens both on mucosal surfaces and in blood and represent a novel approach to control infection. A lysin cloned from a phage infecting GBS was found to contain two putative catalytic domains and one putative binding domain, which is similar to the domain organization of some staphylococcal phage lysins. The lysin (named PlyGBS) was recombinantly expressed in Escherichia coli, and purified PlyGBS efficiently killed all tested GBS serotypes in vitro. In a mouse model, a single dose of PlyGBS significantly reduced bacterial colonization in both the vagina and oropharynx. As an alternative strategy for intrapartum antibiotic prophylaxis, this approach may be used to reduce vaginal GBS colonization in pregnant women before delivery or to decontaminate newborns, thus reducing the incidence of GBS-associated neonatal meningitis and sepsis.
Staphylococcus aureus is an important pathogen, with methicillin-resistant (MRSA) and multi-drug resistant strains becoming increasingly prevalent in both human and veterinary clinics. S. aureus causing bovine mastitis yields high annual losses to the dairy industry. Conventional treatment of mastitis by broad range antibiotics is often not successful and may contribute to development of antibiotic resistance. Bacteriophage endolysins present a promising new source of antimicrobials. The endolysin of prophage ΦSH2 of Staphylococcus haemolyticus strain JCSC1435 (ΦSH2 lysin) is a peptidoglycan hydrolase consisting of two catalytic domains (CHAP and amidase) and an SH3b cell wall binding domain. In this work, we demonstrated its lytic activity against live staphylococcal cells and investigated the contribution of each functional module to bacterial lysis by testing a series of deletion constructs in zymograms and turbidity reduction assays. The CHAP domain exhibited three-fold higher activity than the full length protein and optimum activity in physiological saline. This activity was further enhanced by the presence of bivalent calcium ions. The SH3b domain was shown to be required for full activity of the complete ΦSH2 lysin. The full length enzyme and the CHAP domain showed activity against multiple staphylococcal strains, including MRSA strains, mastitis isolates, and CoNS.
mastitis; phage endolysin; coagulase negative staphylococci
Lysins are phage-encoded, peptidoglycan (cell wall) hydrolases that accumulate in the bacterial cytoplasm during a lytic infection cycle. Late during infection, the lysins undergo holin-mediated translocation across the inner membrane into the peptidoglycan matrix where they cleave cell wall covalent bonds required for wall stability and allow bacterial lysis and progeny phage release. This potent hydrolytic activity is now the foundation of a powerful genetic-based screening process for the identification and analysis of phage lysin proteins. Here, we describe a method for identifying a lysin, PlyG, from a bacteriophage that specifically infects the Gram-positive organism Bacillus anthracis, however, the techniques described can be adapted to clone, express and analyze lysins from any phage infecting Gram-positive bacteria or possibly even Gram-negative bacteria.
lysin; hydrolase; cell wall; peptidoglycan; lysozyme; Gram-positive; antimicrobial; diagnostic; expression library
Treatment of bovine mastitis caused by Staphylococcus (S.) aureus is becoming very difficult due to the emergence of multidrug-resistant strains. Hence, the search for novel therapeutic alternatives has become of great importance. Consequently, bacteriophages and their endolysins have been identified as potential therapeutic alternatives to antibiotic therapy against S. aureus. In the present study, the gene encoding lysin (LysSA4) in S. aureus phage SA4 was cloned and the nucleotide sequence was determined. Sequence analysis of the recombinant clone revealed a single 802-bp open reading frame encoding a partial protein with a calculated mass of 30 kDa. Results of this analysis also indicated that the LysSA4 sequence shared a high homology with endolysin of the GH15 phage and other reported phages. The LysSA4 gene of the SA4 phage was subsequently expressed in Escherichia coli. Recombinant LysSA4 induced the lysis of host bacteria in a spot inoculation test, indicating that the protein was expressed and functionally active. Furthermore, recombinant lysin was found to have lytic activity, albeit a low level, against mastitogenic Staphylococcus isolates of bovine origin. Data from the current study can be used to develop therapeutic tools for treating diseases caused by drug-resistant S. aureus strains.
lysin; mastitis; phage; Staphylococcus aureus
The increased incidence of bacterial antibiotic resistance has led to a renewed search for novel antimicrobials. Avoiding the use of broad-range antimicrobials through the use of specific peptidoglycan hydrolases (endolysins) might reduce the incidence of antibiotic-resistant pathogens worldwide. Staphylococcus aureus and Streptococcus agalactiae are human pathogens and also cause mastitis in dairy cattle. The ultimate goal of this work is to create transgenic cattle that are resistant to mastitis through the expression of an antimicrobial protein(s) in their milk. Toward this end, two novel antimicrobials were produced. The (i) full-length and (ii) 182-amino-acid, C-terminally truncated S. agalactiae bacteriophage B30 endolysins were fused to the mature lysostaphin protein of Staphylococcus simulans. Both fusions display lytic specificity for streptococcal pathogens and S. aureus. The full lytic ability of the truncated B30 protein also suggests that the SH3b domain at the C terminus is dispensable. The fusions are active in a milk-like environment. They are also active against some lactic acid bacteria used to make cheese and yogurt, but their lytic activity is destroyed by pasteurization (63°C for 30 min). Immunohistochemical studies indicated that the fusion proteins can be expressed in cultured mammalian cells with no obvious deleterious effects on the cells, making it a strong candidate for use in future transgenic mice and cattle. Since the fusion peptidoglycan hydrolase also kills multiple human pathogens, it also may prove useful as a highly selective, multipathogen-targeting antimicrobial agent that could potentially reduce the use of broad-range antibiotics in fighting clinical infections.
Phage endolysins are murein hydrolases that break the bacterial cell wall to provoke lysis and release of phage progeny. Recently, these enzymes have also been recognized as powerful and specific antibacterial agents when added exogenously. In the pneumococcal system, most cell wall associated murein hydrolases reported so far depend on choline for activity, and Cpl-7 lysozyme constitutes a remarkable exception. Here, we report the improvement of the killing activity of the Cpl-7 endolysin by inversion of the sign of the charge of the cell wall-binding module (from −14.93 to +3.0 at neutral pH). The engineered variant, Cpl-7S, has 15 amino acid substitutions and an improved lytic activity against Streptococcus pneumoniae (including multiresistant strains), Streptococcus pyogenes, and other pathogens. Moreover, we have demonstrated that a single 25-μg dose of Cpl-7S significantly increased the survival rate of zebrafish embryos infected with S. pneumoniae or S. pyogenes, confirming the killing effect of Cpl-7S in vivo. Interestingly, Cpl-7S, in combination with 0.01% carvacrol (an essential oil), was also found to efficiently kill Gram-negative bacteria such as Escherichia coli and Pseudomonas putida, an effect not described previously. Our findings provide a strategy to improve the lytic activity of phage endolysins based on facilitating their pass through the negatively charged bacterial envelope, and thereby their interaction with the cell wall target, by modulating the net charge of the cell wall-binding modules.
Staphylococci cause bovine mastitis, with Staphylococcus aureus being responsible for the majority of the mastitis-based losses to the dairy industry (up to $2 billion/annum). Treatment is primarily with antibiotics, which are often ineffective and potentially contribute to resistance development. Bacteriophage endolysins (peptidoglycan hydrolases) present a promising source of alternative antimicrobials. Here we evaluated two fusion proteins consisting of the streptococcal λSA2 endolysin endopeptidase domain fused to staphylococcal cell wall binding domains from either lysostaphin (λSA2-E-Lyso-SH3b) or the staphylococcal phage K endolysin, LysK (λSA2-E-LysK-SH3b). We demonstrate killing of 16 different S. aureus mastitis isolates, including penicillin-resistant strains, by both constructs. At 100 μg/ml in processed cow milk, λSA2-E-Lyso-SH3b and λSA2-E-LysK-SH3b reduced the S. aureus bacterial load by 3 and 1 log units within 3 h, respectively, compared to a buffer control. In contrast to λSA2-E-Lyso-SH3b, however, λSA2-E-LysK-SH3b permitted regrowth of the pathogen after 1 h. In a mouse model of mastitis, infusion of 25 μg of λSA2-E-Lyso-SH3b or λSA2-E-LysK-SH3b into mammary glands reduced S. aureus CFU by 0.63 or 0.81 log units, compared to >2 log for lysostaphin. Both chimeras were synergistic with lysostaphin against S. aureus in plate lysis checkerboard assays. When tested in combination in mice, λSA2-E-LysK-SH3b and lysostaphin (12.5 μg each/gland) caused a 3.36-log decrease in CFU. Furthermore, most protein treatments reduced gland wet weights and intramammary tumor necrosis factor alpha (TNF-α) concentrations, which serve as indicators of inflammation. Overall, our animal model results demonstrate the potential of fusion peptidoglycan hydrolases as antimicrobials for the treatment of S. aureus-induced mastitis.
There has been a resurgent interest in the use of bacteriophages or their gene products to control bacterial pathogens as alternatives to currently used antibiotics. Clostridium perfringens is a gram-positive, spore-forming anaerobic bacterium that plays a significant role in human foodborne disease as well as nonfoodborne human, animal, and avian diseases. Countries that have complied with the ban on antimicrobial growth promoters in feeds have reported increased incidences of C. perfringens-associated diseases in poultry. To address these issues, new antimicrobial agents, putative lysins encoded by the genomes of bacteriophages, are being identified in our laboratory. Poultry intestinal material, soil, sewage, and poultry processing drainage water were screened for virulent bacteriophages that could lyse C. perfringens and produce clear plaques in spot assays. Bacteriophages were isolated that had long noncontractile tails, members of the family Siphoviridae, and with short noncontractile tails, members of the family Podoviridae. Several bacteriophage genes were identified that encoded N-acetylmuramoyl-l-alanine amidases, lysozyme-endopeptidases, and a zinc carboxypeptidase domain that has not been previously reported in viral genomes. Putative phage lysin genes (ply) were cloned and expressed in Escherichia coli. The recombinant lysins were amidases capable of lysing both parental phage host strains of C. perfringens as well as other strains of the bacterium in spot and turbidity reduction assays, but did not lyse any clostridia beyond the species. Consequently, bacteriophage gene products could eventually be used to target bacterial pathogens, such as C. perfringens via a species-specific strategy, to control animal and human diseases without having deleterious effects on beneficial probiotic bacteria.
enzybiotic; antibiotic alternative; bacterial virus; food safety; animal/human health
Enterococcus faecalis is increasingly becoming an important nosocomial infection opportunistic pathogen. E. faecalis can easily obtain drug resistance, making it difficult to be controlled in clinical settings. Using bacteriophage as an alternative treatment to drug-resistant bacteria has been revitalized recently, especially for fighting drug-resistant bacteria. In this research, an E. faecalis bacteriophage named IME-EF1 was isolated from hospital sewage. Whole genomic sequence analysis demonstrated that the isolated IME-EF1 belong to the Siphoviridae family, and has a linear double-stranded DNA genome consisting of 57,081 nucleotides. The IME-EF1 genome has a 40.04% G+C content and contains 98 putative coding sequences. In addition, IME-EF1 has an isometric head with a width of 35 nm to 60 nm and length of 75 nm to 90 nm, as well as morphology resembling a tadpole. IME-EF1 can adsorb to its host cells within 9 min, with an absorbance rate more than 99% and a latent period time of 25 min. The endolysin of IME-EF1 contains a CHAP domain in its N-terminal and has a wider bactericidal spectrum than its parental bacteriophage, including 2 strains of vancomycin-resistant E. faecalis. When administrated intraperitoneally, one dose of IME-EF1 or its endolysin can reduce bacterial count in the blood and protected the mice from a lethal challenge of E. faecalis, with a survival rate of 60% or 80%, respectively. Although bacteriophage could rescue mice from bacterial challenge, to the best of our knowledge, this study further supports the potential function of bacteriophage in dealing with E. faecalis infection in vivo. The results also indicated that the newly isolated bacteriophage IME-EF1 enriched the arsenal library of lytic E. faecalis bacteriophages and presented another choice for phage therapy in the future.
Bacteriophage lysins (Ply), or endolysins, are phage-encoded cell wall lytic enzymes which are synthesized late during virus multiplication and mediate the release of progeny virions. Bacteriophages of the pathogen Listeria monocytogenes encode endolysin enzymes which specifically hydrolyze the cross-linking peptide bridges in Listeria peptidoglycan. Ply118 is a 30.8-kDa l-alanoyl-d-glutamate peptidase and Ply511 (36.5 kDa) acts as N-acetylmuramoyl-l-alanine amidase. In order to establish dairy starter cultures with biopreservation properties against L. monocytogenes contaminations, we have introduced ply118 and ply511 into Lactococcus lactis MG1363 by using a pTRKH2 backbone. The genes were expressed under control of the lactococcal promoter P32, which proved superior to other promoters (P21 and P59) tested in this study. High levels of active enzymes were produced and accumulated in the cytoplasmic cell fractions but were not released from the cells at significant levels. Therefore, ply511 was genetically fused with the SPslpA nucleotide sequence encoding the Lactobacillus brevis S-layer protein signal peptide. Expression of SPslpA–ply511 from pSL-PL511 resulted in secretion of functional Ply511 enzyme from L. lactis cells. One clone expressed an unusually strong lytic activity, which was found to be due to a 115-bp deletion that occurred within the 3′-end coding sequence of SPslpA–ply511, which caused a frameshift mutation and generated a stop codon. Surprisingly, the resulting carboxy-terminal deletion of 80 amino acids in the truncated Ply511Δ(S262–K341) mutant polypeptide strongly increased its lytic activity. Proteolytic processing of the secretion competent SPSlpA-Ply511 propeptide following membrane translocation had no influence on enzyme activity. Immunoblotting experiments using both cytoplasmic and supernatant fractions indicated that the enzyme was quantitatively exported from the cells and secreted into the surrounding medium, where it caused rapid lysis of L. monocytogenes cells. Moreover, transformation of pSL-PL511ΔC into L. lactis Bu2-129, a lactose-utilizing strain that can be employed for fermentation of milk, also resulted in secretion of functional enzyme and showed that the vector is compatible with the native lactococcal plasmids.
Endolysins comprise a novel class of selective antibacterials refractory to develop resistances. The Cpl-7 endolysin, encoded by the Streptococcus pneumoniae bacteriophage Cp-7, consists of a catalytic module (CM) with muramidase activity and a cell wall-binding module (CWBM) made of three fully conserved CW_7 repeats essential for activity. Firstly identified in the Cpl-7 endolysin, CW_7 motifs are also present in a great variety of cell wall hydrolases encoded, among others, by human and live-stock pathogens. However, the nature of CW_7 receptors on the bacterial envelope remains unknown. In the present study, the structural stability of Cpl-7 and the target recognized by CW_7 repeats, relevant for exploitation of Cpl-7 as antimicrobial, have been analyzed, and transitions from the CM and the CWBM assigned, using circular dichroism and differential scanning calorimetry. Cpl-7 stability is maximum around 6.0–6.5, near the optimal pH for activity. Above pH 8.0 the CM becomes extremely unstable, probably due to deprotonation of the N-terminal amino-group, whereas the CWBM is rather insensitive to pH variation and its structural stabilization by GlcNAc-MurNAc-l-Ala-d-isoGln points to the cell wall muropeptide as the cell wall target recognized by the CW_7 repeats. Denaturation data also revealed that Cpl-7 is organized into two essentially independent folding units, which will facilitate the recombination of the CM and the CWBM with other catalytic domains and/or cell wall-binding motifs to yield new tailored chimeric lysins with higher bactericidal activities or new pathogen specificities.
The increase in antibiotic resistance world-wide revitalized the interest in the use of phage lysins to combat pathogenic bacteria. In this work, we analyzed the specific cleavage sites on the staphylococcal peptidoglycan produced by three phage lytic proteins. The investigated cell wall lytic enzymes were the endolysin LysH5 derived from the S. aureus bacteriophage vB_SauS-phi-IPLA88 (phi-IPLA88) and two fusion proteins between lysostaphin and the virion-associated peptidoglycan hydrolase HydH5 (HydH5SH3b and HydH5Lyso). We determined that all catalytic domains present in these proteins were active. Additionally, we tested for the emergence of resistant Staphylococcus aureus to any of the three phage lytic proteins constructs. Resistant S. aureus could not be identified after 10 cycles of bacterial exposure to phage lytic proteins either in liquid or plate cultures. However, a quick increase in lysostaphin resistance (up to 1000-fold in liquid culture) was observed. The lack of resistant development supports the use of phage lytic proteins as future therapeutics to treat staphylococcal infections.
The endolysin Lyb5, from Lactobacillus fermentum temperate bacteriophage φPYB5, showed a broad lytic spectrum against Gram-positive as well as Gram-negative bacteria. Sequence analysis revealed that the C terminus of the endolysin Lyb5 (Ly5C) contained three putative lysin motif (LysM) repeat regions, implying that Ly5C was involved in bacterial cell wall binding. To investigate the potential of Ly5C for surface display, green fluorescent protein (GFP) was fused to Ly5C at its N or C terminus and the resulting fusion proteins were expressed in Escherichia coli. After being mixed with various cells in vitro, GFP was successfully displayed on the surfaces of Lactococcus lactis, Lactobacillus casei, Lb. brevis, Lb. plantarum, Lb. fermentum, Lb. delbrueckii, Lb. helveticus, and Streptococcus thermophilus cells. Increases in the fluorescence intensities of chemically pretreated L. lactis and Lb. casei cells compared to those of nonpretreated cells suggested that the peptidoglycan was the binding ligand for Ly5C. Moreover, the pH and concentration of sodium chloride were optimized to enhance the binding capacity of GFP-Ly5C, and high-intensity fluorescence of cells was observed under optimal conditions. All results suggested that Ly5C was a novel anchor for constructing a surface display system for lactic acid bacteria (LAB). To demonstrate the applicability of the Ly5C-mediated surface display system, β-galactosidase (β-Gal) from Paenibacillus sp. strain K1, replacing GFP, was functionally displayed on the surfaces of LAB cells via Ly5C. The success in surface display of GFP and β-Gal opened up the feasibility of employing the cell wall anchor of bacteriophage endolysin for surface display in LAB.
Directed evolution is defined as a method to harness natural selection in order to engineer proteins to acquire particular properties that are not associated with the protein in nature. Literature has provided numerous examples regarding the implementation of directed evolution to successfully alter molecular specificity and catalysis1. The primary advantage of utilizing directed evolution instead of more rational-based approaches for molecular engineering relates to the volume and diversity of variants that can be screened2. One possible application of directed evolution involves improving structural stability of bacteriolytic enzymes, such as endolysins. Bacteriophage encode and express endolysins to hydrolyze a critical covalent bond in the peptidoglycan (i.e. cell wall) of bacteria, resulting in host cell lysis and liberation of progeny virions. Notably, these enzymes possess the ability to extrinsically induce lysis to susceptible bacteria in the absence of phage and furthermore have been validated both in vitro and in vivo for their therapeutic potential3-5. The subject of our directed evolution study involves the PlyC endolysin, which is composed of PlyCA and PlyCB subunits6. When purified and added extrinsically, the PlyC holoenzyme lyses group A streptococci (GAS) as well as other streptococcal groups in a matter of seconds and furthermore has been validated in vivo against GAS7. Significantly, monitoring residual enzyme kinetics after elevated temperature incubation provides distinct evidence that PlyC loses lytic activity abruptly at 45 °C, suggesting a short therapeutic shelf life, which may limit additional development of this enzyme. Further studies reveal the lack of thermal stability is only observed for the PlyCA subunit, whereas the PlyCB subunit is stable up to ~90 °C (unpublished observation). In addition to PlyC, there are several examples in literature that describe the thermolabile nature of endolysins. For example, the Staphylococcus aureus endolysin LysK and Streptococcus pneumoniae endolysins Cpl-1 and Pal lose activity spontaneously at 42 °C, 43.5 °C and 50.2 °C, respectively8-10. According to the Arrhenius equation, which relates the rate of a chemical reaction to the temperature present in the particular system, an increase in thermostability will correlate with an increase in shelf life expectancy11. Toward this end, directed evolution has been shown to be a useful tool for altering the thermal activity of various molecules in nature, but never has this particular technology been exploited successfully for the study of bacteriolytic enzymes. Likewise, successful accounts of progressing the structural stability of this particular class of antimicrobials altogether are nonexistent. In this video, we employ a novel methodology that uses an error-prone DNA polymerase followed by an optimized screening process using a 96 well microtiter plate format to identify mutations to the PlyCA subunit of the PlyC streptococcal endolysin that correlate to an increase in enzyme kinetic stability (Figure 1). Results after just one round of random mutagenesis suggest the methodology is generating PlyC variants that retain more than twice the residual activity when compared to wild-type (WT) PlyC after elevated temperature treatment.
Immunology; Issue 69; Molecular Biology; Genetics; Microbiology; directed evolution; thermal behavior; thermostability; endolysin; enzybiotic; bacteriolytic; antimicrobial; therapeutic; PlyC