Complete Genome of Lactiplantibacillus plantarum 25 (LP25) Isolated from Commercialized Pig Feces

In the world of food and medicine, a specific type of bacteria known as Lactiplantibacillus plantarum holds a special place. It is a microscopic worker found in fermented foods like sauerkraut and pickles, and it is also widely used as a probiotic, a living helper added to food and supplements to support gut health. Because this bacterium is generally recognized as safe by health authorities, scientists often use it as a delivery vehicle for vaccines or as a factory to produce useful proteins. However, as with any living thing introduced into the body, there is a need to understand its genetic makeup completely. Just as a mechanic needs to know every part of an engine before putting it in a car, researchers must map out the entire genetic code of a probiotic strain to ensure it carries no hidden risks, such as genes that could make it resistant to antibiotics, which are medicines used to kill harmful bacteria.

A team of researchers at Kangwon National University in South Korea has now provided this complete genetic map for a specific strain of this bacterium, known as LP25. This particular strain was originally collected from the feces of pigs at a commercial farm and has since become a favorite tool for scientists who want to engineer bacteria to deliver vaccines or study gene expression. The researchers wanted to know exactly what was inside the genetic instruction manual of LP25 to confirm its safety and understand its potential. To do this, they did not just look at a few genes; they sequenced the entire genome, which is the full set of DNA instructions that tells the bacterium how to live and function.

The team used two powerful sequencing technologies to read the DNA. One method reads the genetic code in short, highly accurate snippets, while the other reads much longer stretches of DNA. By combining the results from both methods, they were able to assemble a complete and error-free picture of the bacterium's genetic structure. The final result revealed that LP25 has a single, circular chromosome that is 3,298,237 base pairs long. In addition to this main chromosome, the bacterium carries three smaller, independent rings of DNA called plasmids, which are like extra toolkits the cell can use. The researchers identified 3,172 distinct genes within this genetic material, which act as the instructions for building the proteins the bacterium needs to survive.

When the scientists analyzed these genes, they found several features that explain why this bacterium is so useful. They discovered a cluster of genes responsible for producing plantaricin, a natural substance that can inhibit the growth of other bacteria, which helps the strain compete in its environment. More importantly for safety, they looked for genes that might allow the bacterium to resist antibiotics. Their search found two such genes: one that provides resistance to a type of antibiotic called tetracycline and another that resists a drug called lincomycin. These genes were located on the smaller plasmid rings rather than the main chromosome. The researchers noted that while they found these genetic instructions, they did not test the bacteria in a lab to see if it actually resists the drugs in a living system; they only found the blueprints for resistance.

The study also placed this strain on the family tree of related bacteria. By comparing the core genes of LP25 with those of other similar species, the researchers found that it is most closely related to another strain called L. plantarum W32. This confirms its identity and helps scientists understand how it fits into the broader world of lactic acid bacteria. The complete genetic data, including the maps of the chromosome and plasmids, has been made available to the public through international databases. This allows other scientists to use this information to compare different strains, check for safety in new applications, or design better ways to use this bacterium as a tool for human health.

While the study provides a comprehensive genetic blueprint, the authors are careful to note its boundaries. The data comes from a single isolate, meaning it represents this specific strain and cannot be automatically applied to all L. plantarum bacteria found in the world. Furthermore, the identification of antibiotic resistance genes was done through computer analysis of the DNA sequence, not through physical experiments that measure how the bacteria react to the drugs. Similarly, the presence of the plantaricin genes suggests the bacterium can produce antimicrobial compounds, but the team did not perform tests to confirm that it actually kills other bacteria in a dish. These findings serve as a high-quality reference point, offering a clear and detailed view of the genetic landscape of a widely used probiotic strain, while leaving the final confirmation of its behavior to future laboratory experiments.