Food applications of bacterial cell wall hydrolases

Impact of precursor-derived peracetic acid on post-weaning diarrhea, intestinal microbiota, and predicted microbial functional genes in weaned pigs

Post-weaning diarrhea affects piglets in the nursery phase of production, leading to a substantial impact both at the farm and financial levels. The multifactorial etiology of this disease includes housing conditions, pig genetics, microbial composition, and metagenomic assets. Among the common therapeutic approaches, the widely used zinc oxide underwent a European Union ban in 2022 due to its negative environmental impact and correlation to increased antimicrobial resistance. During this study, we have tested two levels of inclusion of the potential antimicrobial alternative peracetic acid, delivered in water via the hydrolysis of the precursors sodium percarbonate and tetraacetylethylenediamine, in comparison to zinc oxide and an untreated control during a 2-week animal study. We assessed the microbial composition and predicted the metagenome, together with performance and physiological parameters, in order to describe the microbial functional role in etiopathology. Both zinc oxide and peracetic acid resulted in amelioration of the diarrheal status by the end of the trial period, with noticeable zinc oxide effects visible from the first week. This was accompanied by improved performance when compared to the first-week figures and a decreased stomach pH in both peracetic acid levels. A significant reduction in both stomach and caecal Proteobacteria was recorded in the zinc oxide group, and a significant reduction of Campylobacter in the stomach was reported for both zinc oxide and one of the peracetic acid concentrations. Among other functional differences, we found that the predicted ortholog for the zonula occludens toxin, a virulence factor present in pathogens like Escherichia coli and Campylobacter jejuni, was less abundant in the stomach of treated pigs compared to the control group. In water, peracetic acid delivered via precursor hydrolysis has the potential to be a valid intervention, an alternative to antimicrobial, to assist the weaning of piglets. Our findings support the view that post-weaning diarrhea is a complex multifactorial disease with an important metagenomic component characterized by the differential abundance of specific predicted orthologs and microbial genera in the stomach and caecum of pigs.

Making a chink in their armor: Current and next-generation antimicrobial strategies against the bacterial cell envelope

Gram-negative bacteria are uniquely equipped to defeat antibiotics. Their outermost layer, the cell envelope, is a natural permeability barrier that contains an array of resistance proteins capable of neutralizing most existing antimicrobials. As a result, its presence creates a major obstacle for the treatment of resistant infections and for the development of new antibiotics. Despite this seemingly impenetrable armor, in-depth understanding of the cell envelope, including structural, functional and systems biology insights, has promoted efforts to target it that can ultimately lead to the generation of new antibacterial therapies. In this article, we broadly overview the biology of the cell envelope and highlight attempts and successes in generating inhibitors that impair its function or biogenesis. We argue that the very structure that has hampered antibiotic discovery for decades has untapped potential for the design of novel next-generation therapeutics against bacterial pathogens.

Crystal structure of the engineered endolysin mtEC340M

Endolysins produced by bacteriophages play essential roles in the release of phage progeny by degrading the peptidoglycan layers of the bacterial cell wall. Bacteriophage-encoded endolysins have emerged as a new class of antibacterial agents to combat surging antibiotic resistance. The crystal structure of mtEC340M, an engineered endolysin EC340 from the PBEC131 phage that infects Escherichia coli, was determined. The crystal structure of mtEC340M at 2.4 Å resolution consists of eight α-helices and two loops. The three active residues of mtEC340M were predicted by structural comparison with peptidoglycan-degrading lysozyme.

Substantiation of propitious "Enzybiotic" from two novel bacteriophages isolated from a wastewater treatment plant in Qatar

Lysin of bacteriophages isolated from a particular ecosystem could be inducted as a bio-controlling tool against the inhabiting pathogenic bacterial strains. Our study aims at both experimental and computational characterization of the identical lysin gene product inherent in the genomes of two novel Myoviridae bacteriophages, Escherichia Phage C600M2 (GenBank accession number OK040807, Protein ID: UCJ01465) and Escherichia Phage CL1 (GenBank Genome accession number OK040806.1, Protein ID: UCJ01321) isolated from wastewater collected from the main water treatment plant in Qatar. The lysin protein, evinced to be a globular N-acetyl-muramidase with intrinsic “cd00737: endolysin_autolysin” domain, was further expressed and purified to be experimentally validated by turbidimetric assay for its utility as an anti-bacterial agent. Comprehensive computational analysis revealed that the scrutinized lysin protein shared 85–98% sequence identity with 61 bacteriophages, all native to wastewater allied environments. Despite varied Host Recognition Components encoded in their genomes, the similitude of lysins, suggests its apparent significance in host–pathogen interactions endemic to wastewater environment. The present study substantiates the identical lysin from Escherichia Phage C600M2 and Escherichia Phage CL1 as propitious “enzybiotic”, a hybrid term to describe enzymes analogous to anti-biotics to combat antibiotic-resistant bacteria by in silico analysis and subsequent experimental validation.

Assessment of bacteriophage-encoded endolysin as a potent antimicrobial agent against antibiotic-resistant Salmonella Typhimurium

This study was designed to evaluate the potential of using newly purified Salmonella phage-encoded endolysin LysPB32 as novel antibiotic alternative. The endolysin LysPB32 was characterized by analyzing pH and thermal stability, lytic spectrum, antimicrobial activity, and mutant frequency against Salmonella Typhimurium KCCM 40253 (ST^KCCM), S. Typhimurium ATCC 19585 (ST^ATCC), S. Typhimurium CCARM 8009 (ST^CCARM), Klebsiella pneumoniae ATCC 23357 (KP^ATCC), K. pneumoniae CCARM 10237 (KP^CCARM), Pseudomonas aeruginosa ATCC 27853 (PA^ATCC), Listeria monocytogenes ATCC 1911 (LM^ATCC), Staphylococcus aureus ATCC 25923 (SA^ATCC), and S. aureus CCARM 3080 (SA^CCARM). The molecular weight of LysPB32 is 17 kDa that was classified as N-acetyl-β-d-muramidase. The optimum activity of LysPB32 against the outer membrane (OM) permeabilized ST^KCCM, ST^ATCC, and ST^CCARM was observed at 37 °C and pH 6.5. LysPB32 had a broad spectrum of muralytic activity against antibiotic-sensitive ST^KCCM (41 mOD/min), ST^ATCC (32 mOD/min), and SB^KACC (25 mOD/min) and antibiotic-resistant ST^CCARM (35 mOD/min) and KP^CCARM (31 mOD/min). The minimum inhibitory concentrations (MICs) of polymyxin B against ST^KCCM, ST^CCARM, and ST^ATCC were decreased by 4-, 4-, and 8-folds, respectively, when treated with LysPB32. The combination of LysPB32 and polymyxin B effectively inhibited the growth of ST^KCCM, ST^CCARM, and ST^ATCC after 24 h of incubation at 37 °C, showing 4.9-, 4.4-, and 3.3-log reductions, respectively. The mutant frequency was low in ST^KCCM, ST^CCARM, and ST^ATCC treated with combination of LysPB32-polymyxin B system. The results suggest the LysPB32-polymyxin system can be a potential candidate for alternative therapeutic agent to control antibiotic-resistant pathogens.

Isolation and Characterization of a Lytic Staphylococcus aureus Phage WV against Staphylococcus aureus Biofilm

BACKGROUND

Staphylococcus aureus is a Gram-positive, pathogenic bacterium that causes a wide range of symptoms in humans and can form biofilm, which is a multicellular community of microorganisms that attaches to nonbiological and biological surfaces.

METHODS

Here, we aimed to isolate and characterize an S. aureus phage and examine the bactericidal activity alone and in conjunction with streptomycin treatment.

RESULTS

We isolated a virulent phage, WV, from a slaughterhouse in Jiangsu, China. This strain belonged to the family Myoviridae and presented a genome size of 141,342 bp. The optimal pH of the preservation buffer was 6-7, optimal growth temperature was 37°C, and optimal multiplicity of infection was 0.01. Phage WV can sterilize most clinical strains of S. aureus that had been isolated from clinical patients in the First People's Hospital of the Yunnan Province. Against low-concentration S. aureus culture, streptomycin demonstrated a greater antibiofilm effect than that of phage WV. By contrast, in high-concentration S. aureus culture, phage WV demonstrated greater antibiofilm effect than that of streptomycin. The use of phage WV and streptomycin together had a substantially greater overall antibiofilm effect than that achieved using either component alone.

CONCLUSION

This study provides strong evidence for the effectiveness of phage application for the reduction of S. aureus biofilm growth and suggests that phages can be considered as a viable alternative to antibiotics in clinical settings.

Characterization of antibacterial activity of a N-acetylmuramoyl-L-alanine amidase produced by Latilactobacillus sakei isolated from salami

Lactic acid bacteria are the predominant group within meat products, whose metabolites such as bacteriocins and peptidoglycan hydrolases inhibit pathogenic or spoilage bacteria. Fermented meat products, as a salami, is a good source to analyze the viable microbiota, due to these products present a low risk to consumer health. The aim of this work was to identify the lactic acid bacteria with broad antibacterial activity present in salami, purify the protein responsible for this activity, achieve antagonistic spectrum and perform the biochemical characterization. Five strains from salami were selected, isolated and identified by 16S rRNA gene sequencing. The antimicrobial activity was evaluated by antagonism assay and zymography, using spoilage microorganisms commonly found in meat products. The strain that showed a broad antibacterial activity was Latilactobacillus sakei and the antibacterial activity was given by a protein with 75-kDa of molecular mass, identified by LC/MALDI-TOF/TOF. The sequence analysis showed 67% of identity with a N-acetylmuramoyl-L-alanine amidase protein with five non-identical LysM domains. The purified protein showed an optimal pH of 8.0 and heat resistance at 80 °C for 10 min. L. sakei strain displayed antibacterial activity against Gram-negative and Gram-positive spoilage microorganisms. The results of this study provide the information to use Latilactobacillus sakei as a starter culture which will provide the necessary metabolites to combat undesirable microorganisms. Additionally, the conditions and properties for the best application and use of the antibacterial protein produced by this strain. This protein may have a potential use in the food industry as a new antibacterial agent.

Simultaneous Control of Staphylococcus aureus and Bacillus cereus Using a Hybrid Endolysin LysB4EAD-LysSA11

Bacteriophage endolysins have attracted attention as promising alternatives to antibiotics, and their modular structure facilitates endolysin engineering to develop novel endolysins with enhanced versatility. Here, we constructed hybrid proteins consisting of two different endolysins for simultaneous control of two critical foodborne pathogens, Staphylococcus aureus and Bacillus cereus. The full-length or enzymatically active domain (EAD) of LysB4, an endolysin from the B. cereus-infecting phage B4, was fused to LysSA11, an endolysin of the S. aureus-infecting phage SA11, via a helical linker in both orientations. The hybrid proteins maintained the lytic activity of their parental endolysins against both S. aureus and B. cereus, but they showed an extended antimicrobial spectrum. Among them, the EAD of LysB4 fused with LysSA11 (LysB4EAD-LyaSA11) showed significantly increased thermal stability compared to its parental endolysins. LysB4EAD-LysSA11 exhibited high lytic activity at pH 8.0–9.0 against S. aureus and at pH 5.0–10.0 against B. cereus, but the lytic activity of the protein decreased in the presence of NaCl. In boiled rice, treatment with 3.0 µM of LysB4EAD-LysSA11 reduced the number of S. aureus and B. cereus to undetectable levels within 2 h and also showed superior antimicrobial activity to LyB4EAD and LysSA11 in combination. These results suggest that LysB4EAD-LysSA11 could be a potent antimicrobial agent for simultaneous control of S. aureus and B. cereus.

Conformational Differences Are Observed for the Active and Inactive Forms of Pinholin S21 Using DEER Spectroscopy

Bacteriophages have evolved with an efficient host cell lysis mechanism to terminate the infection cycle and release the new progeny virions at the optimum time, allowing adaptation with the changing host and environment. Among the lytic proteins, holin controls the first and rate-limiting step of host cell lysis by permeabilizing the inner membrane at an allele-specific time known as "holin triggering". Pinholin S²¹ is a prototype holin of phage Φ21 which makes many nanoscale holes and destroys the proton motive force, which in turn activates the signal anchor release (SAR) endolysin system to degrade the peptidoglycan layer of the host cell and destruction of the outer membrane by the spanin complex. Like many others, phage Φ21 has two holin proteins: active pinholin and antipinholin. The antipinholin form differs only by three extra amino acids at the N-terminus; however, it has a different structural topology and conformation with respect to the membrane. Predefined combinations of active pinholin and antipinholin fine-tune the lysis timing through structural dynamics and conformational changes. Previously, the dynamics and topology of active pinholin and antipinholin were investigated (Ahammad et al. JPCB 2019, 2020) using continuous wave electron paramagnetic resonance (CW-EPR) spectroscopy. However, detailed structural studies and direct comparison of these two forms of pinholin S²¹ are absent in the literature. In this study, the structural topology and conformations of active pinholin (S²¹68) and inactive antipinholin (S²¹68_IRS) in DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) proteoliposomes were investigated using the four-pulse double electron-electron resonance (DEER) EPR spectroscopic technique to measure distances between transmembrane domains 1 and 2 (TMD1 and TMD2). Five sets of interlabel distances were measured via DEER spectroscopy for both the active and inactive forms of pinholin S²¹. Structural models of the active pinholin and inactive antipinholin forms in DMPC proteoliposomes were obtained using the experimental DEER distances coupled with the simulated annealing software package Xplor-NIH. TMD2 of S²¹68 remains in the lipid bilayer, and TMD1 is partially externalized from the bilayer with some residues located on the surface. However, both TMDs remain incorporated in the lipid bilayer for the inactive S²¹68_IRS form. This study demonstrates, for the first time, clear structural topology and conformational differences between the two forms of pinholin S²¹. This work will pave the way for further studies of other holin systems using the DEER spectroscopic technique and will give structural insight into these biological clocks in molecular detail.

Lysis of cells of diverse bacteria by l,d-peptidases of Escherichia coli bacteriophages RB43, RB49 and T5

AIMS

The objective of this work was to study the antibacterial specificity and antibacterial effect of endolysins isolated from colibacteriophages RB43, RB49 and T5-as manifested on the exponential and stationary cell cultures of diverse bacteria depending on the growth stage, structure of peptidoglycan (PG) and antibiotic resistance.

METHODS AND RESULTS

Enzyme activity was assayed by the spectrophotometric method. Antimicrobial activity was estimated by the number of colony forming units (CFUs), with the results represented as logarithmic units. Morphological examination of bacterial cells was conducted using phase-contrast and scanning electron microscopy. The enzymes EndoT5, endolysin of bacteriophage T5, EndoRB43, endolysin of bacteriophage RB43 and EndoRB49, endolysin of bacteriophage RB49 turned out to be much less bacteriospecific than the corresponding Escherichia coli phages; they lysed bacteria of the genera Bacillus, Cellulomonas and Sporosarcina, whose PGs had different structures (A1γ, A4α and A4β) and chemical modifications (amidation). The specific lytic activity of phage enzymes was independent of the antibiotic resistance of bacterial cells and was higher when the cells were in the exponential, rather than stationary, growth phase. The analysis of morphological changes showed that the intermediate stage of the endolysin-induced lysis of bacterial cells was the formation of spheroplasts and protoplasts.

CONCLUSIONS

Endolysins of colibacteriophages RB49, RB43 and T5 have a wide spectrum of antibacterial action, which includes a number of diverse micro-organisms with different PG structures.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is a study of the bacterial selectivity of enzymes degrading bacterial cell wall in relation to the chemical structure of PG. It is shown that endolysins of bacteriophages RB49 and RB43 efficiently lyse cell wall of Gram-positive bacteria of the genus Bacillus and Gram-negative bacteria of the genus Pseudomonas (including an antibiotic-resistant strain). The number of bacterial cells is reduced by 3-6 orders of magnitude, which indicates good prospects for using these enzymes in biotechnology.

Bacteriophage endolysins as a potential weapon to combat Clostridioides difficile infection

Clostridioides difficile is the leading cause of health-care-associated infection throughout the developed world and contributes significantly to patient morbidity and mortality. Typically, antibiotics are used for the primary treatment of C. difficile infections (CDIs), but they are not universally effective for all ribotypes and can result in antibiotic resistance and recurrent infection, while also disrupting the microbiota. Novel targeted therapeutics are urgently needed to combat CDI. Bacteriophage-derived endolysins are required to disrupt the bacterial cell wall of their target bacteria and are possible alternatives to antibiotics. These lytic proteins could potentially replace or augment antibiotics in CDI treatment. We discuss candidate therapeutic lysins derived from phages/prophages of C. difficile and their potential as antimicrobials against CDI. Additionally, we review the antibacterial potential of some recently identified homologues of C. difficile endolysins. Finally, the challenges of endolysins are considered with respect to the development of novel lysin-based therapies.

Bacteriophage-Derived Endolysins Applied as Potent Biocontrol Agents to Enhance Food Safety

Endolysins, bacteriophage-encoded enzymes, have emerged as antibacterial agents that can be actively applied in food processing systems as food preservatives to control pathogens and ultimately enhance food safety. Endolysins break down bacterial peptidoglycan structures at the terminal step of the phage reproduction cycle to enable phage progeny release. In particular, endolysin treatment is a novel strategy for controlling antibiotic-resistant bacteria, which are a severe and increasingly frequent problem in the food industry. In addition, endolysins can eliminate biofilms on the surfaces of utensils. Furthermore, the cell wall-binding domain of endolysins can be used as a tool for rapidly detecting pathogens. Research to extend the use of endolysins toward Gram-negative bacteria is now being extensively conducted. This review summarizes the trends in endolysin research to date and discusses the future applications of these enzymes as novel food preservation tools in the field of food safety.

Global serum proteomic changes in water buffaloes infected with Fasciola gigantica

BACKGROUND

The liver fluke Fasciola gigantica modulates several signaling pathways in infected buffaloes to facilitate its survival and establishment of persistent infection. In response to the parasite invasion, buffaloes activate innate and adaptive immune responses to counter the parasite infection. To detect new proteins that might be involved in the interaction between F. gigantica and the buffaloes, and that also might serve as biomarkers for fasciolosis, we used proteomic techniques to study the serum proteome of buffaloes during F. gigantica infection. Here, we used an isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic approach to identify serum proteins that are differentially expressed in infected buffaloes compared to uninfected control buffaloes. Additionally, we applied a parallel reaction monitoring (PRM) assay to validate specific proteins identified by the iTRAQ method.

RESULTS

A total of 313, 459 and 399 proteins were identified at 3, 42 and 70 days post-infection, respectively; of these 92, 93 and 138 were differentially abundant proteins. Some of the identified differentially abundant proteins, including complement factor H related 5, complement component C6, complement component C7, amine oxidase, plasma serine protease inhibitor and lysozyme, are known to be involved in complement system activation, blood coagulation, platelet activation, lymphocyte's adhesion and lysozyme hydrolysis. Analysis of data for all three time points after infection identified six significantly upregulated proteins in infected serum that separated infected and uninfected buffaloes into distinct clusters. Further PRM analysis confirmed the expression of five proteins, namely MHC class I antigen, Beta-2-microglobulin, NID2 protein, Fetuin-B and Fibrinogen gamma-B chain.

CONCLUSIONS

These findings provide novel insights into the serum proteomics signature of buffaloes during F. gigantica infection.

Lactic acid bacteria isolated from dairy products as potential producers of lipolytic, proteolytic and antibacterial proteins

Regular consumption of fermented dairy products helps maintain a healthy microbiota and prevent gut dysbiosis-linked diseases. The lactic acid bacteria (LAB) present in food enhance the digestibility of proteins, moderate the release of fatty acids, and support human health through inhabiting the gastrointestinal tract. These desirable properties of LAB are attributed, in part, to their metabolic processes involving enzymes such as lipases, proteases, and antibacterial proteins. The LAB strains presenting higher enzymatic activities may offer improved functionality for applications in foods. The first aim of this work was to isolate and identify LAB from diverse dairy products and select those with enhanced enzymatic activities. Secondly, this work aimed to investigate the subcellular organization and identity of these enzymes after semi-purification. Out of the total 137 LAB strains isolated and screened, 50.3% and 61.3% of the strains exhibited lipolytic and proteolytic activities, respectively. Seven strains displaying high enzymatic activities were selected and further characterized for the cellular organization of their lipases, proteases, and antibacterial proteins. The lipolytic and proteolytic activities were exhibited predominantly in the extracellular fraction; whereas, the antibacterial activities were found in various cellular fractions and were capable of inhibiting common undesirable microorganisms in foods. In total, two lipases, seven proteases, and three antibacterial proteins were identified by LC-MS/MS. Characterization of LAB strains with high enzymatic activity has potential biotechnological significance in fermentative processes and in human health as they may improve the physicochemical characteristics of foods and displace strains with weaker enzymatic activities in the human gut microbiota.

Phage-Derived Antibacterials: Harnessing the Simplicity, Plasticity, and Diversity of Phages

Despite the successful use of antibacterials, the emergence of multidrug-resistant bacteria has become a serious threat to global healthcare. In this era of antibacterial crisis, bacteriophages (phages) are being explored as an antibacterial treatment option since they possess a number of advantages over conventional antibacterials, especially in terms of specificity and biosafety; phages specifically lyse target bacteria while not affecting normal and/or beneficial bacteria and display little or no toxicity in that they are mainly composed of proteins and nucleic acids, which consequently significantly reduces the time and cost involved in antibacterial development. However, these benefits also create potential issues regarding antibacterial spectra and host immunity; the antibacterial spectra being very narrow when compared to those of chemicals, with the phage materials making it possible to trigger host immune responses, which ultimately disarm antibacterial efficacy upon successive treatments. In addition, phages play a major role in horizontal gene transfer between bacterial populations, which poses serious concerns for the potential of disastrous consequences regarding antibiotic resistance. Fortunately, however, recent advancements in synthetic biology tools and the speedy development of phage genome resources have allowed for research on methods to circumvent the potentially disadvantageous aspects of phages. These novel developments empower research which goes far beyond traditional phage therapy approaches, opening up a new chapter for phage applications with new antibacterial platforms. Herein, we not only highlight the most recent synthetic phage engineering and phage product engineering studies, but also discuss a new proof-of-concept for phage-inspired antibacterial design based on the studies undertaken by our group.

Enzybiotics: Enzyme-Based Antibacterials as Therapeutics

Antibiotics have saved millions of lives. However, the overuse and misuse of antibiotics have contributed to a rapid emergence of antibiotic resistance worldwide. In addition, there is an unprecedented void in the development of new antibiotic classes by the pharmaceutical industry since the first introduction of antibiotics. This antibiotic crisis underscores the urgent and increasing necessity of new, innovative antibiotics. Enzybiotics are such a promising class of antibiotics. They are derived from endolysins, bacteriophage-encoded enzymes that degrade the bacterial cell wall of the infected cell at the end of the lytic replication cycle. Enzybiotics are featured by a rapid and unique mode-of-action, a high specificity to kill pathogens, a low probability for bacterial resistance development and a proteinaceous nature. (Engineered) endolysins have been demonstrated to be effective in a variety of animal models to combat both Gram-positive and Gram-negative bacteria and have entered different phases of preclinical and clinical trials. In addition, mycobacteriophage-encoded endolysins have been successfully used to inhibit mycobacteria in vitro. In this chapter we focus on the (pre)clinical progress of enzybiotics as potent therapeutic agent against human pathogenic bacteria.

Structural insights into the binding and catalytic mechanisms of the Listeria monocytogenes bacteriophage glycosyl hydrolase PlyP40

Endolysins are bacteriophage-encoded peptidoglycan hydrolases that specifically degrade the bacterial cell wall at the end of the phage lytic cycle. They feature a distinct modular architecture, consisting of enzymatically active domains (EADs) and cell wall-binding domains (CBDs). Structural analysis of the complete enzymes or individual domains is required for better understanding the mechanisms of peptidoglycan degradation and provides guidelines for the rational design of chimeric enzymes. We here report the crystal structure of the EAD of PlyP40, a member of the GH-25 family of glycosyl hydrolases, and the first muramidase reported for Listeria phages. Site-directed mutagenesis confirmed key amino acids (Glu98 and Trp10) involved in catalysis and substrate stabilization. In addition, we found that PlyP40 contains two heterogeneous CBD modules with homology to SH3 and LysM domains. Truncation analysis revealed that both domains are required for full activity but contribute to cell wall recognition and lysis differently. Replacement of CBDP40 with a corresponding domain from a different Listeria phage endolysin yielded an enzyme with a significant shift in pH optimum. Finally, domain swapping between PlyP40 and the streptococcal endolysin Cpl-1 produced an intergeneric chimera with activity against Listeria cells, indicating that structural similarity of individual domains determines enzyme function.

Bacteriophages and Their Immunological Applications against Infectious Threats

Bacteriophage therapy dates back almost a century, but the discovery of antibiotics led to a rapid decline in the interests and investments within this field of research. Recently, the novel threat of multidrug-resistant bacteria highlighted the alarming drop in research and development of new antibiotics: 16 molecules were discovered during 1983–87, 10 new therapeutics during the nineties, and only 5 between 2003 and 2007. Phages are therefore being reconsidered as alternative therapeutics. Phage display technique has proved to be extremely promising for the identification of effective antibodies directed against pathogens, as well as for vaccine development. At the same time, conventional phage therapy uses lytic bacteriophages for treatment of infections and recent clinical trials have shown great potential. Moreover, several other approaches have been developed in vitro and in vivo using phage-derived proteins as antibacterial agents. Finally, their use has also been widely considered for public health surveillance, as biosensor phages can be used to detect food and water contaminations and prevent bacterial epidemics. These novel approaches strongly promote the idea that phages and their proteins can be exploited as an effective weapon in the near future, especially in a world which is on the brink of a “postantibiotic era.”

Prediction of peptidoglycan hydrolases- a new class of antibacterial proteins

Background

The efficacy of antibiotics against bacterial infections is decreasing due to the development of resistance in bacteria, and thus, there is a need to search for potential alternatives to antibiotics. In this scenario, peptidoglycan hydrolases can be used as alternate antibacterial agents due to their unique property of cleaving peptidoglycan cell wall present in both gram-positive and gram-negative bacteria. Along with a role in maintaining overall peptidoglycan turnover in a cell and in daughter cell separation, peptidoglycan hydrolases also play crucial role in bacterial pathophysiology requiring development of a computational tool for the identification and classification of novel peptidoglycan hydrolases from genomic and metagenomic data.

Results

In this study, the known peptidoglycan hydrolases were divided into multiple classes based on their site of action and were used for the development of a computational tool ‘HyPe’ for identification and classification of novel peptidoglycan hydrolases from genomic and metagenomic data. Various classification models were developed using amino acid and dipeptide composition features by training and optimization of Random Forest and Support Vector Machines. Random Forest multiclass model was selected for the development of HyPe tool as it showed up to 71.12 % sensitivity, 99.98 % specificity, 99.55 % accuracy and 0.80 MCC in four different classes of peptidoglycan hydrolases. The tool was validated on 24 independent genomic datasets and showed up to 100 % sensitivity and 0.94 MCC. The ability of HyPe to identify novel peptidoglycan hydrolases was also demonstrated on 24 metagenomic datasets.

Conclusions

The present tool helps in the identification and classification of novel peptidoglycan hydrolases from complete genomic or metagenomic ORFs. To our knowledge, this is the only tool available for the prediction of peptidoglycan hydrolases from genomic and metagenomic data.

Availability: http://metagenomics.iiserb.ac.in/hype/ and http://metabiosys.iiserb.ac.in/hype/.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2753-8) contains supplementary material, which is available to authorized users.

Bacteriophage endolysins: applications for food safety

Bacteriophage endolysins (peptidoglycan hydrolases) have emerged as a new class of antimicrobial agents useful for controlling bacterial infection or other unwanted contaminations in various fields, particularly in the light of the worldwide increasing frequency of drug-resistant pathogens. This review summarizes and discusses recent developments regarding the use of endolysins for food safety. Besides the use of native and engineered endolysins for controlling bacterial contamination at different points within the food production chain, this also includes the application of high-affinity endolysin-derived cell wall binding domains for rapid detection of pathogenic bacteria. Novel approaches to extend the lytic action of endolysins towards Gram-negative cells will also be highlighted.

The potential of the endolysin Lysdb from Lactobacillus delbrueckii phage for combating Staphylococcus aureus during cheese manufacture from raw milk

Phage endolysins have received increased attention in recent times as potential antibacterial agents and the biopreservatives in food production processes. Staphylococcus aureus is one of the most common pathogens in bacterial food poisoning outbreaks. In this study, the endolysin Lysdb, one of the two-component cell lysis cassette of Lactobacillus delbrueckii phage phiLdb, was shown to possess a muramidase domain and catalytic sites with homology to Chalaropsis-type lysozymes. Peptidoglycan hydrolytic bond specificity determination revealed that Lysdb was able to cleave the 6-O-acetylated peptidoglycans present in the cell walls of S. aureus. Turbidity reduction assays demonstrated that Lysdb could effectively lyse the S. aureus live cells under acidic and mesothermal conditions. To further evaluate the ability of Lysdb as a potential antibacterial agent against S. aureus in cheese manufacture, Lactobacillus casei BL23 was engineered to constitutively deliver active Lysdb to challenge S. aureus in lab-scale cheese making from raw milk. Compared with the raw milk, the viable counts of S. aureus were reduced by 10(5)-fold in the cheese inoculated with the engineered L. casei strain during the fermentation process, and the pathogenic bacterial numbers remained at a low level (10(4) CFU/g) after 6 weeks of ripening at 10 °C. Taken together, all results indicated that the Lysdb has the function as an effective tool for combating S. aureus during cheese manufacture from raw milk.

Antibacterial Activity of Stenotrophomonas maltophilia Endolysin P28 against both Gram-positive and Gram-negative Bacteria

Maltocin P28 is a phage-tail like bacteriocin produced by Stenotrophomonas maltophilia P28. The ORF8 of maltocin P28 gene cluster is predicted to encode an endolysin and we name it endolysin P28. Sequence analysis revealed that it contains the lysozyme_like superfamily conserved domain. Endolysin P28 has the four consensus motifs as that of Escherichia coli phage lambda gpR. In this study, endolysin P28 was expressed in E. coli BL21 (DE3) and purified with a C-terminal oligo-histidine tag. The antibacterial activity of endolysin P28 increased as the temperature rose from 25 to 45°C. Thermostability assays showed that endolysin P28 was stable up to 50°C, while its residual activity was reduced by 55% after treatment at 70°C for 30 min. Acidity and high salinity could enhance its antibacterial activity. Endolysin P28 exhibited a broad antibacterial activity against 14 out of 16 tested Gram-positive and Gram-negative bacteria besides S. maltophilia. Moreover, it could effectively lyse intact Gram-negative bacteria in the absence of ethylenediaminetetraacetic acid as an outer membrane permeabilizer. Therefore, the characteristics of endolysin P28 make it a potential therapeutic agent against multi-drug-resistant pathogens.

Characterisation of the antibacterial properties of a bacterial derived peptidoglycan hydrolase (LysCs4), active against C. sakazakii and other Gram-negative food-related pathogens

Illness caused by the consumption of contaminated food products continues to represent one of the main challenges facing food manufacturers worldwide. Even with current intervention technologies and increased hygiene measures, foodborne illness remains a significant threat to public health. This coupled with the increasing emergence of multidrug resistant pathogens has increased the need for the development of novel technologies for pathogen control. Bacterial derived peptidoglycan hydrolases represent a vast and highly diverse group of enzymes with potential for biocontrol of a range of Gram-positive and Gram-negative foodborne pathogens. In this study, we describe the identification, cloning, expression and purification of a peptidoglycan hydrolase (LysCs4) derived from Cronobacter sakazakii for biocontrol of the aforementioned infant formula pathogen itself. In silico analysis of LysCs4 revealed the gene to display greatest sequence similarity to a putative lysozyme encoded by the lytic Cronobacter phage ES2. Conserved domain analysis of LysCs4 revealed the presence of a single catalytic domain predicted to display O-Glycosyl hydrolase activity and to be a member of the GH24 family. The ability of this enzyme to hydrolyse the peptidoglycan of 25 Gram-negative strains, across 4 different genera, highlights its potential as a novel candidate for biocontrol of C. sakazakii and other Gram-negative food related pathogens.

Bacteriophages and bacteriophage-derived endolysins as potential therapeutics to combat Gram-positive spore forming bacteria

Since their discovery in 1915, bacteriophages have been routinely used within Eastern Europe to treat a variety of bacterial infections. Although initially ignored by the West due to the success of antibiotics, increasing levels and diversity of antibiotic resistance is driving a renaissance for bacteriophage-derived therapy, which is in part due to the highly specific nature of bacteriophages as well as their relative abundance. This review focuses on the bacteriophages and derived lysins of relevant Gram-positive spore formers within the Bacillus cereus group and Clostridium genus that could have applications within the medical, food and environmental sectors.

Expression, purification, and characterization of a bifunctional 99-kDa peptidoglycan hydrolase from Pediococcus acidilactici ATCC 8042

Pediococcus acidilactici ATCC 8042 is a lactic acid bacteria that inhibits pathogenic microorganisms such as Staphylococcus aureus through the production of two proteins with lytic activity, one of 110 kDa and the other of 99 kDa. The 99-kDa one has high homology to a putative peptidoglycan hydrolase (PGH) enzyme reported in the genome of P. acidilactici 7_4, where two different lytic domains have been identified but not characterized. The aim of this work was the biochemical characterization of the recombinant enzyme of 99 kDa. The enzyme was cloned and expressed successfully and retains its activity against Micrococcus lysodeikticus. It has a higher N-acetylglucosaminidase activity, but the N-acetylmuramoyl-L-alanine amidase can also be detected spectrophotometrically. The protein was then purified using gel filtration chromatography. Antibacterial activity showed an optimal pH of 6.0 and was stable between 5.0 and 7.0. The optimal temperature for activity was 60 °C, and all activity was lost after 1 h of incubation at 70 °C. The number of strains susceptible to the recombinant 99-kDa enzyme was lower than that susceptible to the mixture of the 110- and 99-kDa PGHs of P. acidilactici, a result that suggests synergy between these two enzymes. This is the first PGH from LAB that has been shown to possess two lytic sites. The results of this study will aid in the design of new antibacterial agents from natural origin that can combat foodborne disease and improve hygienic practices in the industrial sector.

Functional analysis of the N-terminal region of endolysin Lyb5 encoded by Lactobacillus fermentum bacteriophage φPYB5

Lactobacillus fermentum temperate bacteriophage φPYB5 uses endolysin Lyb5 and holin Hyb5 to burst the host cell. Previous results showed that expression of Lyb5 in Escherichia coli caused host cell lysis slowly, leading us to suppose that Lyb5 could pass the cytoplasmic membrane partly. In this work, the function of a putative signal peptide (SPLyb5) at the N-terminal of Lyb5 was investigated. In E. coli, the cell adopted a spherical shape during induction of Lyb5 protein, while morphological changes were not observed during expression of the SPLyb5 truncation, indicating that the SPLyb5 motif may serve as a functional signal peptide. However, SPLyb5 was not proteolytically cleaved at the predicted site during the translocation of Lyb5, and the expressed Lyb5 protein appeared in the cytoplasm, cytoplasmic membrane and periplasm fractions with the same molecular mass. Similar results were obtained using Lactococcus lactis as a host to express Lyb5. These results indicated that SPLyb5 could direct Lyb5 to the periplasm in a membrane-tethered form, and then release it as a soluble active enzyme into the periplasm. In addition, SPLyb5 could also drive the fused NucleaseB protein to the extracytoplasm environment in E. coli as well as in L. lactis. We proposed that in Gram-negative and Gram-positive hosts SPLyb5 acted as a signal-anchor-release domain, which was firstly identified here by experimental evidences in lactic acid bacteria phages. The application of signal-anchor-release domain for endolysin export in bacteriophages infecting Gram-positive and Gram-negative hosts was discussed.

Phage lytic proteins: biotechnological applications beyond clinical antimicrobials

Most bacteriophages encode two types of cell wall lytic proteins: endolysins (lysins) and virion-associated peptidoglycan hydrolases. Both enzymes have the ability to degrade the peptidoglycan of Gram-positive bacteria resulting in cell lysis when they are applied externally. Bacteriophage lytic proteins have a demonstrated potential in treating animal models of infectious diseases. There has also been an increase in the study of these lytic proteins for their application in areas such as food safety, pathogen detection/diagnosis, surfaces disinfection, vaccine development and nanotechnology. This review summarizes the more recent developments, outlines the full potential of these proteins to develop new biotechnological tools and discusses the feasibility of these proposals.

Bacteriophage PBC1 and its endolysin as an antimicrobial agent against Bacillus cereus

Bacillus cereus is an opportunistic human pathogen responsible for food poisoning and other, nongastrointestinal infections. Due to the emergence of multidrug-resistant B. cereus strains, the demand for alternative therapeutic options is increasing. To address these problems, we isolated and characterized a Siphoviridae virulent phage, PBC1, and its lytic enzymes. PBC1 showed a very narrow host range, infecting only 1 of 22 B. cereus strains. Phylogenetic analysis based on the major capsid protein revealed that PBC1 is more closely related to the Bacillus clarkii phage BCJA1c and phages of lactic acid bacteria than to the phages infecting B. cereus. Whole-genome comparison showed that the late-gene region, including the terminase gene, structural genes, and holin gene of PBC1, is similar to that from B. cereus temperate phage 250, whereas their endolysins are different. Compared to the extreme host specificity of PBC1, its endolysin, LysPBC1, showed a much broader lytic spectrum, albeit limited to the genus Bacillus. The catalytic domain of LysPBC1 when expressed alone also showed Bacillus-specific lytic activity, which was lower against the B. cereus group but higher against the Bacillus subtilis group than the full-length protein. Taken together, these results suggest that the virulent phage PBC1 is a useful component of a phage cocktail to control B. cereus, even with its exceptionally narrow host range, as it can kill a strain of B. cereus that is not killed by other phages, and that LysPBC1 is an alternative biocontrol agent against B. cereus.

Next generation sequencing technologies and the changing landscape of phage genomics

The dawn of next generation sequencing technologies has opened up exciting possibilities for whole genome sequencing of a plethora of organisms. The 2nd and 3rd generation sequencing technologies, based on cloning-free, massively parallel sequencing, have enabled the generation of a deluge of genomic sequences of both prokaryotic and eukaryotic origin in the last seven years. However, whole genome sequencing of bacterial viruses has not kept pace with this revolution, despite the fact that their genomes are orders of magnitude smaller in size compared with bacteria and other organisms. Sequencing phage genomes poses several challenges; (1) obtaining pure phage genomic material, (2) PCR amplification biases and (3) complex nature of their genetic material due to features such as methylated bases and repeats that are inherently difficult to sequence and assemble. Here we describe conclusions drawn from our efforts in sequencing hundreds of bacteriophage genomes from a variety of Gram-positive and Gram-negative bacteria using Sanger, 454, Illumina and PacBio technologies. Based on our experience we propose several general considerations regarding sample quality, the choice of technology and a "blended approach" for generating reliable whole genome sequences of phages.

Engineered bacteriophage lysins as novel anti-infectives

Bacteriophage lysins, the highly evolved specific peptidoglycan hydrolases, have long been demonstrated to be effective enzybiotics in various infectious models. The modular structure of lysins makes it possible to design bioengineered lysins that have desired properties, such as higher activity, or broader killing spectrum. Moreover, lysins can even be engineered to kill Gram-negative bacterial pathogens from without, a property that is not present in natural lysins. In this era of ever increasing multidrug resistant pathogens, engineered lysins represent a new class of enzybiotics that are powerful and readily available to fight antimicrobial resistance.

Food and feed enzymes

Humans have benefited from the unique catalytic properties of enzymes, in particular for food production, for thousands of years. Prominent examples include the production of fermented alcoholic beverages, such as beer and wine, as well as bakery and dairy products. The chapter reviews the historic background of the development of modern enzyme technology and provides an overview of the industrial food and feed enzymes currently available on the world market. The chapter highlights enzyme applications for the improvement of resource efficiency, the biopreservation of food, and the treatment of food intolerances. Further topics address the improvement of food safety and food quality.

Holins in bacteria, eukaryotes, and archaea: multifunctional xenologues with potential biotechnological and biomedical applications

Holins form pores in the cytoplasmic membranes of bacteria for the primary purpose of releasing endolysins that hydrolyze the cell wall and induce cell death. Holins are encoded within bacteriophage genomes, where they promote cell lysis for virion release, and within bacterial genomes, where they serve a diversity of potential or established functions. These include (i) release of gene transfer agents, (ii) facilitation of programs of differentiation such as those that allow sporulation and spore germination, (iii) contribution to biofilm formation, (iv) promotion of responses to stress conditions, and (v) release of toxins and other proteins. There are currently 58 recognized families of holins and putative holins with members exhibiting between 1 and 4 transmembrane α-helical spanners, but many more families have yet to be discovered. Programmed cell death in animals involves holin-like proteins such as Bax and Bak that may have evolved from bacterial holins. Holin homologues have also been identified in archaea, suggesting that these proteins are ubiquitous throughout the three domains of life. Phage-mediated cell lysis of dual-membrane Gram-negative bacteria also depends on outer membrane-disrupting "spanins" that function independently of, but in conjunction with, holins and endolysins. In this minireview, we provide an overview of their modes of action and the first comprehensive summary of the many currently recognized and postulated functions and uses of these cell lysis systems. It is anticipated that future studies will result in the elucidation of many more such functions and the development of additional applications.

Biochemical characterization of the major N-acetylmuramidase from Lactobacillus buchneri

Bacterial cell wall hydrolases are essential for peptidoglycan remodelling in regard to bacterial cell growth and division. In this study, peptidoglycan hydrolases (PGHs) of different Lactobacillus buchneri strains were investigated. First, the genome sequence of L. buchneri CD034 and L. buchneri NRRL B-30929 was analysed in silico for the presence of PGHs. Of 23 putative PGHs with different predicted hydrolytic specificities, the glycosyl hydrolase family 25 domain-containing homologues LbGH25B and LbGH25N from L. buchneri CD034 and NRRL B-30929, respectively, were selected and characterized in detail. Zymogram analysis confirmed hydrolysing activity on bacterial cell walls for both enzymes. Subsequent reversed-phase HPLC and MALDI-TOF MS analysis of the peptidoglycan breakdown products from L. buchneri strains CD034 and NRRL B-30929, and from Lactobacillus rhamnosus GG, which served as a reference, revealed that LbGH25B and LbGH25N have N-acetylmuramidase activity. Both enzymes were identified as cell wall-associated proteins by means of immunofluorescence microscopy and cellular fractionation, as well as by the ability of purified recombinant LbGH25B and LbGH25N to bind to L. buchneri cell walls in vitro. Moreover, similar secondary structures mainly composed of β-sheets and nearly identical thermal stabilities with T m values around 49 °C were found for the two N-acetylmuramidases by far-UV circular dichroism spectroscopy. The functional and structural data obtained are discussed and compared to related PGHs. In this study, a major N-acetylmuramidase from L. buchneri was characterized in detail for the first time.

Art-175 is a highly efficient antibacterial against multidrug-resistant strains and persisters of Pseudomonas aeruginosa

Artilysins constitute a novel class of efficient enzyme-based antibacterials. Specifically, they covalently combine a bacteriophage-encoded endolysin, which degrades the peptidoglycan, with a targeting peptide that transports the endolysin through the outer membrane of Gram-negative bacteria. Art-085, as well as Art-175, its optimized homolog with increased thermostability, are each composed of the sheep myeloid 29-amino acid (SMAP-29) peptide fused to the KZ144 endolysin. In contrast to KZ144, Art-085 and Art-175 pass the outer membrane and kill Pseudomonas aeruginosa, including multidrug-resistant strains, in a rapid and efficient (∼ 5 log units) manner. Time-lapse microscopy confirms that Art-175 punctures the peptidoglycan layer within 1 min, inducing a bulging membrane and complete lysis. Art-175 is highly refractory to resistance development by naturally occurring mutations. In addition, the resistance mechanisms against 21 therapeutically used antibiotics do not show cross-resistance to Art-175. Since Art-175 does not require an active metabolism for its activity, it has a superior bactericidal effect against P. aeruginosa persisters (up to >4 log units compared to that of the untreated controls). In summary, Art-175 is a novel antibacterial that is well suited for a broad range of applications in hygiene and veterinary and human medicine, with a unique potential to target persister-driven chronic infections.

The novel Shewanella putrefaciens-infecting bacteriophage Spp001: genome sequence and lytic enzymes

Shewanella putrefaciens has been identified as a specific spoilage organism commonly found in chilled fresh fish, which contributes to the spoilage of fish products. Limiting S. putrefaciens growth can extend the shelf-life of chilled fish. Endolysins, which are lytic enzymes produced by bacteriophages, have been considered an alternative to control bacterial growth, and have been useful in various applications, including food preservation. We report here, for the first time, the complete genome sequence of a novel phage Spp001, which lyses S. putrefaciens Sp225. The Spp001 genome comprises a 54,789-bp DNA molecule with 67 open reading frames and an average total G + C content of 49.42 %. In silico analysis revealed that the Spp001 open reading frames encode various putative functional proteins, including an endolysin (ORF 62); however, no sequence for genes encoding the holin polypeptides, which work in concert with endolysins, was identified. To examine further the lytic activity of Spp001, we analyzed the lytic enzyme-containing fraction from phages released at the end of the phage lytic cycle in S. putrefaciens, using diffusion and turbidimetric assays. The results show that the partially purified extract contained endolysin, as indicated by a high hydrolytic activity towards bacterial peptidoglycan decrease in the OD590 value by 0.160 in 15 min. The results will allow further investigation of the purification of natural Spp001 endolysin, the extension of Spp001 host range, and the applications of the phage-encoded enzymes.

Structure of bacteriophage SPN1S endolysin reveals an unusual two-module fold for the peptidoglycan lytic and binding activity

Bacteriophage SPN1S infects the pathogenic Gram-negative bacterium Salmonella typhimurium and expresses endolysin for the release of phage progeny by degrading peptidoglycan of the host cell walls. Bacteriophage SPN1S endolysin exhibits high glycosidase activity against peptidoglycans, resulting in antimicrobial activity against a broad range of outer membrane-permeabilized Gram-negative bacteria. Here, we report a crystal structure of SPN1S endolysin, indicating that unlike most endolysins from Gram-negative bacteria background, the α-helical protein consists of two modular domains, a large and a small domain, with a concave groove between them. Comparison with other structurally homologous glycoside hydrolases indicated a possible peptidoglycan binding site in the groove, and the presence of a catalytic dyad in the vicinity of the groove, one residue in a large domain and the other in a junction between the two domains. The catalytic dyad was further validated by antimicrobial activity assay against outer membrane-permeabilized Escherichia coli. The three-helix bundle in the small domain containing a novel class of sequence motif exhibited binding affinity against outer membrane-permeabilized E. coli and was therefore proposed as the peptidoglycan-binding domain. These structural and functional features suggest that endolysin from a Gram-negative bacterial background has peptidoglycan-binding activity and performs glycoside hydrolase activity through the catalytic dyad.

Novel highly thermostable endolysin from Thermus scotoductus MAT2119 bacteriophage Ph2119 with amino acid sequence similarity to eukaryotic peptidoglycan recognition proteins

In this study, we present the discovery and characterization of a highly thermostable endolysin from bacteriophage Ph2119 infecting Thermus strain MAT2119 isolated from geothermal areas in Iceland. Nucleotide sequence analysis of the 16S rRNA gene affiliated the strain with the species Thermus scotoductus. Bioinformatics analysis has allowed identification in the genome of phage 2119 of an open reading frame (468 bp in length) coding for a 155-amino-acid basic protein with an Mr of 17,555. Ph2119 endolysin does not resemble any known thermophilic phage lytic enzymes. Instead, it has conserved amino acid residues (His(30), Tyr(58), His(132), and Cys(140)) that form a Zn(2+) binding site characteristic of T3 and T7 lysozymes, as well as eukaryotic peptidoglycan recognition proteins, which directly bind to, but also may destroy, bacterial peptidoglycan. The purified enzyme shows high lytic activity toward thermophiles, i.e., T. scotoductus (100%), Thermus thermophilus (100%), and Thermus flavus (99%), and also, to a lesser extent, toward mesophilic Gram-negative bacteria, i.e., Escherichia coli (34%), Serratia marcescens (28%), Pseudomonas fluorescens (13%), and Salmonella enterica serovar Panama (10%). The enzyme has shown no activity against a number of Gram-positive bacteria analyzed, with the exception of Deinococcus radiodurans (25%) and Bacillus cereus (15%). Ph2119 endolysin was found to be highly thermostable: it retains approximately 87% of its lytic activity after 6 h of incubation at 95°C. The optimum temperature range for the enzyme activity is 50°C to 78°C. The enzyme exhibits lytic activity in the pH range of 6 to 10 (maximum at pH 7.5 to 8.0) and is also active in the presence of up to 500 mM NaCl.

Functional analysis of SleC from Clostridium difficile: an essential lytic transglycosylase involved in spore germination

Clostridium difficile is the most common cause of enteric disease and presents a major burden on healthcare systems globally due in part to the observed rapid rise in antibiotic resistance. The ability of C. difficile to form endospores is a key feature in the organism's pathogenesis and transmission, and contributes greatly to its resilient nature. Endospores are highly resistant to disinfection, allowing them to persist on hospital surfaces. In order for the organism to cause disease, the spores must germinate and revert to a vegetative form. While spore germination in Bacillus spp. is well understood, very little is known about this process in Clostridia. Here we report the characterization of SleC (CD0551) from C. difficile 630. Bioinformatic analysis of SleC indicated a multi-domained protein possessing a peptidoglycan-binding (PGB) domain, a SpoIID/LytB domain and an undefined N-terminal region. We have confirmed that SleC is an exo-acting lytic transglycosylase with the catalytic activity localized to the N-terminal region. Additionally, we have shown that both the N-terminal catalytic domain and the C-terminal PGB domain require muramyl-δ-lactam for substrate binding. As with carbohydrate-binding modules from cellulases and xylanases, the PGB domain may be responsible for increasing the processivity of SleC by concentrating the enzyme at the surface of the substrate.