Shirota Strain: Advancing Probiotic Research for Better Health
Explore the Shirota strain’s role in probiotic research, its microbiological traits, cultivation methods, and genetic insights for potential health benefits.
Probiotics play a crucial role in gut health, and the Shirota strain has gained attention for its benefits. Isolated by Dr. Minoru Shirota in the 1930s, this bacterial strain is widely studied for its effects on digestion, immunity, and overall well-being.
Research continues to explore how this probiotic interacts with the human microbiome, offering insights into its properties and applications.
Classification In Microbiology
Lacticaseibacillus casei Shirota belongs to the Lactobacillaceae family, a group of lactic acid bacteria that ferment carbohydrates into lactic acid. Initially classified under Lactobacillus, taxonomic revisions in 2020 by Zheng et al. placed it in the Lacticaseibacillus genus. This reclassification, based on whole-genome sequencing and phylogenetic analysis, provides a clearer understanding of its genetic and functional traits.
It is a Gram-positive, facultatively anaerobic bacterium, meaning it can survive in both oxygen-rich and oxygen-deprived environments. Its rod-shaped, non-spore-forming structure is typical of lactic acid bacteria, which thrive in dairy products and the human gastrointestinal tract. Phylogenetic studies using 16S rRNA sequencing confirm its close relationship with other Lacticaseibacillus species, but its metabolic profile and probiotic properties set it apart.
Beyond its genetic classification, L. casei Shirota is recognized as a probiotic due to its ability to confer health benefits when consumed in adequate amounts. The Food and Agriculture Organization (FAO) and the World Health Organization (WHO) define probiotics based on their ability to survive gastric transit, adhere to intestinal cells, and modulate gut microbiota. L. casei Shirota meets these criteria, as it withstands acidic environments and can temporarily colonize the intestines. This makes it a key ingredient in functional foods, such as the well-known Yakult beverage.
Physical And Biochemical Characteristics
The Shirota strain has distinct physical and biochemical characteristics that contribute to its probiotic function. Morphologically, it is a rod-shaped, Gram-positive bacterium measuring 2.0–4.0 µm in length and 0.8–1.0 µm in width. Its shape aids in adhering to intestinal epithelial cells, a key trait for gut colonization. It is non-motile and does not form spores, relying on favorable conditions for survival. When cultured on de Man, Rogosa, and Sharpe (MRS) agar, it forms smooth, convex, creamy-white colonies, distinguishing it from other bacteria.
Metabolically, L. casei Shirota is facultatively anaerobic, allowing it to survive in both oxygenated and anaerobic environments. It primarily ferments carbohydrates to produce lactic acid, which lowers pH and inhibits pathogenic microorganisms. The strain predominantly produces L-(+)-lactic acid, which is more biocompatible with human metabolism, reducing the risk of lactic acidosis.
The strain also expresses β-galactosidase, aiding lactose digestion, and has proteolytic activity, breaking down proteins into bioactive peptides. It metabolizes various sugars, including glucose, fructose, and maltose, enabling it to thrive in diverse dietary conditions. Additionally, it exhibits moderate bile salt tolerance, a crucial trait for survival in the small intestine.
Laboratory Cultivation Methods
Cultivating Lacticaseibacillus casei Shirota requires precise environmental control. It thrives in de Man, Rogosa, and Sharpe (MRS) broth, which provides essential nutrients and maintains an optimal pH of 6.2–6.5. The ideal incubation temperature is 37°C, mimicking the human gut environment. Under these conditions, the strain follows a typical growth curve, reaching the stationary phase within 18–24 hours.
While it can survive in both aerobic and anaerobic settings, its growth is enhanced under microaerophilic conditions. This is achieved by culturing in sealed containers or anaerobic chambers with controlled gas compositions. Cysteine hydrochloride can further reduce oxygen levels, improving viability. The strain also tolerates moderate bile salt concentrations, an adaptive trait for intestinal survival.
For long-term preservation, cryopreservation techniques such as freezing in glycerol (15–20%) or skim milk prevent ice crystal damage. Lyophilization (freeze-drying) allows the strain to remain stable at room temperature, crucial for probiotic formulations. Quality control measures, including periodic colony-forming unit (CFU) counts, ensure stored cultures maintain their probiotic properties.
Genetic Profile Insights
The genome of Lacticaseibacillus casei Shirota is approximately 2.9 megabases, encoding over 2,900 genes. Its genetic makeup supports carbohydrate metabolism, enabling it to utilize various sugars and persist in the fluctuating nutrient conditions of the gastrointestinal tract. Comparative genomic analyses reveal shared core genes with other Lacticaseibacillus species, but L. casei Shirota possesses unique clusters for acid and bile resistance.
Mobile genetic elements, such as plasmids and transposons, contribute to adaptability, though L. casei Shirota has a relatively stable genome with limited horizontal gene transfer. This stability ensures consistency in probiotic function across production batches. The strain also carries genes encoding surface-layer proteins that facilitate adhesion to intestinal cells, a key factor in modulating gut microbiota and interacting with host cells.