Natural Transformation and GFP Expression in the Filamentous Cyanobacterium Phormidium lacuna
JoVE Encyclopedia of Experiments
Microbiology
0 views • 4:37 min • October 30th, 2025
Take a culture of Phormidium lacuna, a filamentous cyanobacterium.
Homogenize the culture to disperse the filaments, then centrifuge to pellet the bacteria.
Discard the supernatant and resuspend the pellet in nutrient-rich media.
Add plasmid DNA containing green fluorescent protein and antibiotic-resistance genes onto an antibiotic-supplemented agar plate.
Add the bacterial suspension over the DNA and incubate under light conditions.
The bacteria internalize the DNA using type IV pili. The introduced genes integrate into one of the multiple copies of the bacterial genome.
Redistribute the bacteria onto an antibiotic-supplemented agar plate to select the transformed bacteria.
Under a light microscope, identify healthy, green filaments indicating successful transformation.
Transfer the selected filaments to liquid media with a higher antibiotic concentration to enrich the transformed population.
Again, plate them onto agar with higher antibiotic levels for segregating transformants.
Visualize GFP expression under a fluorescence microscope to confirm successful transformation.
Begin by inoculating 50 milliliters liquid F2 medium into each of the two 250-milliliter flasks with one milliliter of P. lacuna filaments from a running culture. Cultivate in white light under agitation for around five days at 25 degrees Celsius.
After five days, homogenize 100 milliliters of P. lacuna cell suspension at 10,000 RPM for three minutes and measure the optical density at 750 nanometers. Then, centrifuge the cell suspension for 15 minutes at 6,000 times g. Remove the supernatant and suspend the pellet in 800 microliters of the remaining liquid and additional F2+ medium. Take eight F2+ Bacto agar plates containing 120 micrograms per milliliter kanamycin and pipette 10 micrograms of DNA into the middle of each agar plate.
Immediately pipette 100 microliters of the cell suspension on top of the DNA. Keep the agar plate without a lid on the clean bench to allow the excess liquid to evaporate. Close the plate and cultivate it in white light at 25 degrees Celsius for two days.
After two days, distribute the filaments of each agar plate onto several fresh F2+ Bacto agar plates containing 120 micrograms per milliliter kanamycin with an inoculation loop. Cultivate the plates in white light at 25 degrees Celsius and check the cultures regularly under a microscope. After 14 to 28 days, identify the dead brownish filaments and search for transformed filaments under the microscope.
The transformed filaments look healthy and green and are different from the bulk of filaments. Transfer each single transformed filament into 50-milliliter flasks with 10 milliliters of F2+ medium with 250 micrograms per milliliter kanamycin. Cultivate in white light at 25 degrees Celsius on a shaker and observe growth for up to four weeks.
Transfer the filaments back to the agar medium containing 250 micrograms per milliliter kanamycin and wait for the filaments to grow. Then, increase the kanamycin concentration again to speed up the segregation. For GFP expression, observes single filaments with a fluorescence microscope at 40X or 63X magnification and capture a bright-field transmission image and a fluorescence image.
Overview
This study details the transformation of the filamentous cyanobacterium Phormidium lacuna using plasmid DNA. The process involves the internalization of DNA via type IV pili and subsequent selection of transformed bacteria.
Key Study Components
Area of Science
- Microbiology
- Genetic Engineering
- Cyanobacteria Research
Background
- Phormidium lacuna is a filamentous cyanobacterium.
- Transformation techniques are essential for genetic studies.
- Green fluorescent protein (GFP) is commonly used as a reporter gene.
- Antibiotic resistance genes facilitate the selection of transformed cells.
Purpose of Study
- To successfully transform Phormidium lacuna with plasmid DNA.
- To visualize GFP expression as an indicator of successful transformation.
- To establish a method for enriching transformed cyanobacterial populations.
Methods Used
- Homogenization and centrifugation of cyanobacterial cultures.
- Resuspension in nutrient-rich media and plating on antibiotic-supplemented agar.
- Incubation under light conditions to promote transformation.
- Microscopic evaluation of transformed filaments for GFP expression.
Main Results
- Successful internalization of plasmid DNA by Phormidium lacuna.
- Identification of healthy, green filaments indicating successful transformation.
- Enrichment of transformed populations through selective plating.
- Visualization of GFP expression confirmed successful genetic transformation.
Conclusions
- The method effectively transforms Phormidium lacuna with plasmid DNA.
- GFP serves as a reliable marker for successful transformation.
- This approach can be applied to other cyanobacterial species for genetic studies.
Frequently Asked Questions
Executive Industry Relevance
Establishing reliable genetic transformation in filamentous cyanobacteria enables target validation and mechanistic de-risking for photosynthetic pathway engineering and sustainable bioproduction. Stable GFP expression provides a quantitative, visual readout for assessing genetic construct performance and pathway modulation in a disease-relevant system. This approach supports preclinical model development by generating engineered strains with predictable phenotypic outputs for lead identification and predictive confidence in early discovery.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of therapeutic hypotheses in photosynthetic metabolism and redox regulation pathways.
- Operational Value: Provides a scalable system for functional target validation via homologous recombination and marker gene expression.
- Predictive Value: Supports predictive confidence by linking genotype to GFP-linked phenotypic output under controlled light conditions.
Screening & Assay Development
- Scientific Value: Generates standardized, transformable cyanobacterial strains for assay preparation and compound screening.
- Operational Value: Enables assay reproducibility through antibiotic selection and clonal segregation of transformed filaments.
- Platform Value: Establishes a reusable platform for evaluating genetic constructs and promoter strength via fluorescence quantification.
Translational & Preclinical Research
- Scientific Value: Facilitates disease-relevant system modeling by engineering cyanobacteria to produce therapeutic metabolites or signaling molecules.
- Operational Value: Supports translational biomarker alignment through constitutive or inducible GFP expression as a transformation efficiency reporter.
- Risk Mitigation: Enables risk-adjusted advancement decisions by quantifying genetic stability and expression consistency over subculture.
Pipeline & Workflow Integration
The method fits within the discovery continuum from target validation through lead identification, providing a chassis for photosynthetic engineering and metabolite production.
- Discovery Biology: Supports hypothesis testing of gene function in cyanobacterial metabolism via targeted integration and phenotypic screening.
- Screening: Delivers assay readiness through standardized transformation efficiency and selectable marker expression.
- Analytics: Enables quantitative comparison of genetic constructs via fluorescence intensity and growth kinetics under selection.
- Translational Research: Connects to preclinical continuity by generating engineered strains with stable, measurable outputs for pathway validation.
- Enterprise Reuse: Establishes a platform technology for iterative design-build-test cycles in synthetic biology and metabolic engineering.
Operational & Enterprise Impact
- Scientific Value: Predictive confidence in genetic manipulation, reduction of mechanistic ambiguity in photosynthetic systems.
- Operational Value: Standardization, reproducibility, and scalability of transformation workflows across laboratories.
- Strategic Value: Improved go/no-go decisions in strain engineering, capital efficiency in biosynthetic pathway optimization.
- Portfolio Impact: Risk-adjusted prioritization of cyanobacterial chassis based on transformation efficiency and genetic tractability.
Implementation Considerations
- Requires expertise in microbiology, molecular cloning, and microscopy for transformation and visualization.
- Dependent on sterile technique, light-controlled incubators, and fluorescence imaging infrastructure.
- Necessitates standardization of antibiotic selection protocols and filament handling procedures.
- Adaptation considerations include optimizing DNA concentration, incubation time, and selection stringency for different cyanobacterial strains.
- Practical limitations include transformation efficiency variability and the need for prolonged selection to achieve segregants.
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Last updated: 29 August 2026