Gene Editing of Klebsiella pneumoniae Phage
1. Research Background
Klebsiella pneumoniae is a common Gram‑negative opportunisticpathogen in clinical settings. The widespread spread of carbapenem‑resistant Klebsiellapneumoniae (CRKP) has become a major threat to global public health. Asviruses that specifically kill target pathogenic bacteria, bacteriophages showgreat potential for the treatment of drug‑resistant bacterial infections.However, natural phages are often limited by narrow host range, poor biofilmpenetration, and other drawbacks. Precise and efficient gene editingtechnologies provide a key tool for engineering phage properties and expandingtheir applications in clinical therapy and detection.
Against this background, Shutong Bio provides customizedengineering services for Klebsiella pneumoniae phages. Using theCRISPR/Cas9 counter‑selection system or BRED (Bacteriophage Recombineering ofElectroporated DNA) technology, we achieve precise genome editing includingtarget gene knockout, point mutation, and exogenous gene integration (such ascapsule depolymerase). We deliver positive mutant phage strains after multiplerounds of purification.
2. Host Characteristics and Biological Background
(1) Host Cell Wall and Capsule Properties
The most prominent feature of Klebsiella pneumoniae is itsthick polysaccharide capsule. This barrier not only protects the bacterium fromimmune attacks but also determines the recognition specificity of phages.
(2) Clinical Background
Research on CRKP and hypervirulent Klebsiella pneumoniae(hvKp) represents a major current challenge. Engineered phages can specificallydegrade the capsules of particular serotypes.
(3) Phage Diversity
Klebsiella pneumoniae phages include members of the Siphoviridae,Podoviridae, and Myoviridae families. They often encode various depolymerasesto penetrate bacterial capsules.
3. Reported Editing Strategies
Given the rapidreplication and lysis of Klebsiella pneumoniae phage genomes in hostbacteria, the mainstream editing strategies include:
3.1 CRISPR/Cas9‑AssistedSelection System (Core Strategy)
(1) Principle:Cas9 and sgRNA targeting wild‑type phage are pre‑introduced into host bacteria.During phage infection, Cas9 cleaves the wild‑type genome, while editedrecombinants survive due to altered target sites.
(2) Advantages:Greatly improves the extremely low mutation efficiency of traditionalhomologous recombination (often below 10⁻⁴), enabling highly efficientscreening.
3.2 HomologousRecombination
Using the hostrecombination system (e.g., λ‑Red system), donor DNA containing mutatedsequences is introduced during phage DNA replication.
3.3 In VitroAssembly & Rebooting
The phage genome isfragmented, modified and ligated in vitro, then introduced into competent hostcells by electroporation for virion packaging.
4. Core ApplicationAreas
(1) Host RangeExpansion: Perform point mutations or domain swapping on tail fiber orreceptor‑binding proteins (RBPs) to alter phage host specificity.
(2) EnhancedBiofilm Degradation: Integrate potent capsule depolymerase or depolymerasegene clusters into the phage genome to strengthen degradation of biofilmsformed by clinical drug‑resistant strains.
(3) SyntheticBiology Engineering: Integrate fluorescent protein or luciferase genes forrapid detection of Klebsiella pneumoniae in clinical samples.
(4) FunctionalGenomics: Precisely delete non‑essential or lysis‑related genes to studyphage infection mechanisms.
5. Project Workflow& Validation
We provide one‑stopservices from design to delivery to ensure accurate editing results:
(1) Design &Vector Construction: Design mutation templates, sgRNAs against wild‑typephage, and corresponding selection plasmids.
(2) Host StrainEngineering: Introduce the CRISPR system and donor DNA into recipient Klebsiellapneumoniae.
(3) PhageScreening & Enrichment: Infect engineered bacteria with wild‑type phageand enrich edited progeny using Cas9 selection pressure.
(4) Single‑PlaqueValidation: Perform 3–5 rounds of single‑plaque purification, combined withPCR identification and whole‑genome sequencing to confirm positive mutations.
6. Gene Editing Project Introduction
6.1 Core Services
(1) Gene Knockout/ Inactivation
Precise deletion ofunnecessary virulence‑related genes or non‑essential fragments.
(2) GeneIntegration / Overexpression
Insertion ofexogenous sequences such as depolymerases or fluorescent reporters intointergenic regions or non‑essential gene loci.
(3) Precise PointMutation
Site‑specificmodification of key amino acids in receptor‑binding proteins (RBPs).
(4) MultisiteEditing
Sequentialmodification of multiple tail fiber proteins or regulatory genes.
6.2 TechnicalAdvantages
(1) HighSpecificity: Extensive experience with host bacteria and phages of variousserotypes including K1, K2, K47, K64, etc.
(2) High‑EfficiencyScreening: Optimized CRISPR selection system improves screening efficiencyto over 80%.
(3) RapidDelivery: Standardized workflows ensure confirmed mutant phages aredelivered in the shortest time.
7. Case Study
Case: AntimicrobialPotential of a Novel K5‑Specific Phage and Its Recombinant Strains against Klebsiellapneumoniae in Milk
Project Description: A novel K5‑specific phage and itsengineered recombinant strains were constructed and systematically evaluatedfor antibacterial activity against Klebsiella pneumoniae in milk.
(1) ResearchBackground
Milk is rich innutrients and provides an ideal environment for bacterial growth. Klebsiellapneumoniae is an important pathogen causing bovine mastitis and dairyproduct contamination. With the growing problem of antibiotic resistance,including the emergence of carbapenem‑ and colistin‑resistant strains, phagetherapy has emerged as a promising alternative strategy. However, most currentstudies focus on K1 and K2 serotypes. Phage resources targeting thehypervirulent K5 serotype, which is prevalent in Chinese dairy farms, remainscarce, and their application potential in dairy products has not been fullyexplored. This study aims to fill this gap by developing K5‑specific phagetools to provide new strategies for dairy product safety.
(2) Project Design
The research teamconstructed and optimized phage resources through a multi‑step engineeringstrategy:
Phage Isolation and Identification
K1‑specific phagesP284, P287 and K5‑specific phage P252 were isolated from hospital sewage. Theirmorphology was confirmed by electron microscopy (e.g., P252 is a Podoviridaewith a head diameter of 58 ± 0.5 nm). Genome sequencing confirmed the absenceof lysogenic, virulence, or antibiotic resistance genes, meeting biosafetyrequirements.
Receptor‑Binding Protein (RBP) Engineering
The phage genome wasselectively edited using the CRISPR‑Cas9 system. The RBP of K1‑specific phageP284 was replaced with the RBP of K5‑specific phage P252, generatingrecombinant phages T and F. This approach switched the host range from K1 to K5via homologous recombination, significantly expanding phage library diversity.
Activity Evaluation System
Antibacterialefficacy was systematically evaluated under different multiplicities ofinfection (MOI = 10, 1, 0.1) using planktonic assays and a milk model (4°C forcold storage, 38°C for room temperature).
(3) Experimental Conclusions
Recombinant phagesexhibit superior antibacterial activity
In planktonicassays, recombinant phages T and F showed significantly stronger inhibitionagainst the K5 strain than wild‑type P252 at MOI = 10, reducing bacterialcounts by up to 2.99 log₁₀ cfu/mL (P < 0.001) with a more durableinhibitory effect (remaining highly effective within 12 hours). Recombinantphages still formed degradation halos on some non‑lytic K5 strains, indicatingthat their RBPs can specifically recognize capsular polysaccharides.
Efficient bacterialinhibition in milk
Under refrigerationat 4°C, all K5‑specific phages (P252, T, F) significantly reduced bacterialload within 9 hours (up to 2.70 log₁₀ cfu/mL reduction), with inhibitionpositively correlated with MOI. At 38°C, the phage‑treated groups completelysuppressed bacterial fermentation (while vigorous fermentation occurred in thecontrol group), demonstrating application potential at both temperatures.
Safety validation
Genomic analysisconfirmed no insertion of harmful genes in recombinant phages, and their narrowlytic spectrum avoided impacts on non‑target microflora.
(4) ApplicationSignificance
Pollution control inthe dairy industry
This study is thefirst to demonstrate the efficacy of K5‑specific phages under both refrigeratedand ambient conditions in milk, providing a novel biocontrol tool forpreventing dairy spoilage and bovine mastitis. The engineering strategy forrecombinant phages can be extended to other serotypes, enabling precise “one‑strain‑one‑strategy”prevention and control.
Expansion of phagetherapy resources
CRISPR‑Cas9‑mediatedhost range modification provides a technical paradigm for rapidly constructingtargeted phage libraries, overcoming the regulatory complexity of traditionalphage cocktail therapy.
Future directions
Further evaluationis needed of phage stability in real dairy production chains, as well as thepotential of combining phages with depolymerases to improve clearanceefficiency against drug‑resistant strains.
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