A breakthrough in understanding the molecular mechanisms of Lyme disease pathogenesis
Imagine taking a peaceful hike through a lush forest, only to return home with an unwelcome souvenir—a tiny tick bite that could transmit Lyme disease, a potentially debilitating illness. This scenario plays out thousands of times annually across the Northern Hemisphere, all caused by a remarkable spiral-shaped bacterium called Borrelia burgdorferi. What if I told you that Chinese scientists have made a crucial breakthrough in understanding this pathogen by cloning and expressing one of its most important genes?
At the heart of this story lies flagellin, the building block of the bacterium's propeller-like flagella that enables it to move through its environment and invade our tissues.
Recently, researchers successfully cloned and expressed the flagellin gene from a Chinese Borrelia burgdorferi PD91 strain, opening new possibilities for improved diagnosis and understanding of Lyme disease 1 . This achievement represents more than just laboratory work—it's a step toward potentially better protecting people from this emerging infectious disease.
Flagellin forms the bacterial flagellum enabling corkscrew movement through tissues.
The flagellin gene serves as a genetic fingerprint for identifying Borrelia species.
Flagellin enables accurate species identification for targeted treatment.
Flagellin is the primary structural protein that forms the bacterial flagellum—a sophisticated rotating filament that functions as an outboard motor for bacteria. In Borrelia burgdorferi, these internal flagella are tucked between the inner and outer membranes, contributing to the bacterium's distinctive corkscrew movement through tissues. This unique motility is essential for the bacterium to disseminate through host tissues and establish infection.
The flagellin protein possesses a fascinating modular architecture—its ends are highly conserved across bacterial species, ensuring proper structural assembly, while its middle region varies significantly. This variable section contains unique sequences that contribute to strain-specific characteristics and antigenic properties 3 . When our immune system encounters flagellin, it recognizes it as a foreign invader and produces specific antibodies—a response that scientists can harness for diagnostic purposes.
The flagellin gene serves as a genetic fingerprint for identifying Borrelia species and strains. Different Borrelia species possess characteristic sequences in their flagellin genes, much like different car models have distinct engine designs. This genetic variation enables researchers to develop specific tests that can not only detect the presence of the Lyme disease bacterium but determine exactly which species is causing an infection 7 .
Recent research has revealed that the flagellin gene is so distinctive between Borrelia species that it can be used for accurate species identification 4 . This is crucial because different Borrelia species may cause varying symptoms and require different treatment approaches. The genetic sequence of the flagellin gene thus becomes both a structural blueprint and a diagnostic tool in the fight against Lyme disease.
In 2004, Chinese researchers embarked on a project to clone and express the flagellin gene from a local Borrelia burgdorferi strain designated PD91. Their experimental approach followed a systematic pathway:
Using the polymerase chain reaction (PCR) technique, the scientists amplified the specific DNA sequence coding for the flagellin protein from the PD91 strain's genetic material 1 .
The amplified gene was then inserted into a recombinant plasmid—a circular DNA molecule that can be replicated inside bacterial cells. This plasmid served as a molecular vehicle to transport the flagellin gene into host bacteria 1 .
The engineered plasmids were introduced into Escherichia coli BL21 strain bacteria. These microbial factories were then induced to produce the flagellin protein encoded by the inserted gene 1 .
The researchers confirmed the successful expression of the flagellin protein using SDS-PAGE (a method to separate proteins by size) and Western blot analysis (which identifies specific proteins using antibodies) 1 .
The experimental results yielded several important discoveries. The cloned flagellin gene from the PD91 strain measured 1,011 base pairs in length—the fundamental units of the genetic code. When compared with the North American B31 reference strain, the Chinese PD91 strain showed 94.70% genetic similarity at the DNA level and 95.85% similarity at the protein level 1 . While these percentages might seem high, they represent significant genetic differences that could influence disease presentation and diagnosis.
| Genetic Feature | Measurement | Comparison to B31 Strain |
|---|---|---|
| Gene Length | 1,011 base pairs | Not specified |
| DNA Sequence Homology | Not applicable | 94.70% |
| Amino Acid Sequence Homology | Not applicable | 95.85% |
| Recombinant Protein Expression | Successful in E. coli BL21 | Not applicable |
Most importantly, the recombinant flagellin protein produced by the E. coli factories demonstrated the same immunological properties as the natural flagellin from the PD91 strain. This meant that the cloned version could reliably be used in diagnostic tests and further research 1 .
Molecular biology research relies on specialized reagents and materials that enable scientists to manipulate genetic material. The following table presents key components used in flagellin gene cloning and expression, drawing from the PD91 study and related research:
| Reagent/Material | Function in Research | Specific Examples from Studies |
|---|---|---|
| Expression Vectors | DNA vehicles for gene insertion and protein production | Recombinant plasmids 1 |
| Host Organisms | Living systems for propagating genes and producing proteins | E. coli BL21 strain 1 |
| PCR Primers | Target-specific DNA sequences for gene amplification | Degenerate primers for flagellin |
| Detection Antibodies | Identify and confirm protein expression | Western blot analysis 1 |
| Restriction Enzymes | Molecular scissors for cutting DNA at specific sites | Enzymes for diagnostic RFLP 7 |
The step-by-step process used by the researchers ensured that the cloned gene was both accurate and functional. The use of E. coli BL21 as an expression host was particularly strategic—this strain is specially engineered to efficiently produce recombinant proteins without degrading them 1 .
The verification process was equally crucial. The Western blot analysis confirmed that the immune system recognizes the laboratory-produced flagellin identically to the natural version. This validation step guaranteed that the cloned protein could serve as a reliable substitute for natural flagellin in future applications, particularly in developing diagnostic tests that detect antibodies in patient blood samples 1 .
The successful cloning of the PD91 flagellin gene has immediate practical applications in Lyme disease diagnostics. Currently, diagnosing Lyme disease remains challenging due to its variable symptoms and the limitations of existing tests. The recombinant flagellin protein produced through this research can serve as a standardized antigen in serological tests, potentially improving their accuracy and reliability.
Researchers have developed sophisticated molecular methods that leverage flagellin gene sequences for pathogen detection. One particularly effective approach is flagellin gene-based nested PCR, which enables scientists to detect extremely small quantities of Borrelia DNA in patient samples with high sensitivity. When combined with restriction fragment length polymorphism (RFLP) analysis, this method can both identify the presence of Borrelia and determine the specific species causing infection 7 .
| Detection Method | Target | Number of Positive Pools Detected |
|---|---|---|
| flaB Gene-Based Profiling | flaB gene | 83 |
| Nested PCR | flaB gene | 58 |
| V4 rrs Profiling | rrs gene | 56 |
The implications of flagellin research extend far beyond Lyme disease diagnostics. Recent studies have revealed fascinating applications of flagellin in immunotherapy and vaccine development. In 2025, researchers discovered that engineering CAR-T cells to express Salmonella flagellin could potentially enhance their ability to fight solid tumors by activating additional immune responses 8 . This innovative approach demonstrates how bacterial proteins can be harnessed for cutting-edge cancer treatments.
Studies on segmented filamentous bacteria have shown that their flagellin plays a crucial role in guiding immune system development 5 . These commensal bacteria use flagellin to adhere to intestinal cells and stimulate protective immune responses.
The genetic tools and methodologies developed through the PD91 flagellin cloning project continue to support new discoveries. As next-generation sequencing technologies advance, flagellin gene profiling has emerged as a powerful method for tracking Borrelia diversity.
The successful cloning and expression of the flagellin gene from the Chinese Borrelia burgdorferi PD91 strain represents more than a technical achievement—it provides a critical tool for understanding Lyme disease pathogens and developing better diagnostics. This work highlights how studying the fundamental components of bacteria can lead to practical applications that potentially improve human health.
From enabling precise pathogen detection to revealing new possibilities in cancer immunotherapy, flagellin research continues to yield surprising discoveries. As scientists build upon these findings, each cloned gene brings us closer to mastering the complex interactions between pathogens and their hosts. The flagellin gene of Borrelia burgdorferi, once merely the blueprint for a bacterial propeller, has become a key to unlocking multiple scientific mysteries—demonstrating how basic molecular research can spin in unexpected and valuable directions.