Investigating the Probiotic Potential of Saccharomyces Boulardii
Understanding Probiotics
Probiotics are typically consumed after a course of antibiotics, which eliminate most gut bacteria. The primary purpose of taking probiotics is to restore the balance of beneficial microorganisms that can combat harmful bacteria. Defined as live microorganisms that provide health benefits to the host, probiotics are predominantly bacterial; however, a unique species of yeast, Saccharomyces boulardii, also qualifies as a probiotic.
The Origins of Saccharomyces Boulardii
Saccharomyces boulardii was first isolated from litchis in Indochina and is classified under the Saccharomyces cerevisiae species, commonly known for its use in baking and brewing. Notably, S. boulardii is the only yeast that has undergone evaluation for its probiotic effects in double-blinded clinical trials.
Mechanisms of Action
S. boulardii offers health benefits through two primary mechanisms. It inhibits certain bacterial toxins and their damaging effects while also exerting immunostimulatory effects on the intestinal mucosa. Researchers aimed to determine if this yeast could effectively prevent the growth of harmful bacteria.
Acetic Acid Production and Its Effects
Recent research published in Genome Research by Belgian scientists explored whether S. boulardii could inhibit bacterial growth and the genetic factors responsible for this probiotic effect. The study assessed the antibacterial activity of twelve different strains of S. boulardii alongside eleven strains of S. cerevisiae as controls.
The researchers conducted tests by placing a drop of cell-free culture media from the yeast onto a surface hosting Escherichia coli MG1655 in a petri dish. Results indicated that three out of the twelve S. boulardii strains exhibited antibacterial properties. Acetic acid, the main component of vinegar, was identified as the substance responsible for preventing bacterial growth. All twelve S. boulardii strains produced moderate to high levels of acetic acid, particularly in comparison to S. cerevisiae. However, the levels of acetic acid decreased over time in the nine S. boulardii strains lacking antimicrobial effects, suggesting they were consuming the acid as concentrations rose.
Genetic Insights into Acetic Acid Production
To further understand the genetic basis of acetic acid production and utilization, the researchers employed genome sequencing. They discovered a mutation in the sdh1 gene present in all S. boulardii strains, which led to enhanced acetic acid production. Additionally, a mutation in the whi2 gene was found to impair the yeast’s ability to utilize acetic acid, resulting in higher concentrations.
The research team then genetically modified S. cerevisiae, which does not produce acetic acid, by introducing these mutations either separately or in combination. While single mutations showed no impact on acetic acid production, the introduction of all mutations collectively increased production levels. This work allowed the researchers to establish a genetic fingerprint that differentiates S. boulardii from S. cerevisiae, marking the first identification of a genetic signature for S. boulardii.
Implications and Future Research
Prof. Thevelein, the principal investigator of the study, noted in a press release the significance of identifying unique mutations in S. boulardii that contribute to acetic acid production. These genetic markers facilitate the distinction between various yeast types and aid in isolating new S. boulardii strains from natural sources.
Despite the promising findings regarding the probiotic characteristics of S. boulardii, certain limitations must be acknowledged. The study relied on a single bacterial strain to assess the probiotic effect, making it essential to explore how high acetic acid production influences different pathogenic bacteria strains. Furthermore, understanding the impact of acetic acid on commensal gut bacteria is crucial before categorizing S. boulardii as a definitive probiotic.
References
Czerucka, D., Piche, T. & Rampal, P. “Yeast as probiotics–Saccharomyces boulardii.” Alimentary Pharmacology & Therapeutics 26, 767-778 (2007).
Butel, M.-J. “Probiotics, gut microbiota and health.” Médecine et Maladies Infectieuses 44, 1-8 (2014).
Oelschlaeger, T. A. “Mechanisms of probiotic actions–a review.” International Journal of Medical Microbiology 300, 57-62 (2010).
Guarner, F. & Malagelada, J.-R. “Gut flora in health and disease.” The Lancet 361, 512-519 (2003).
Sears, C. L. “A dynamic partnership: celebrating our gut flora.” Anaerobe 11, 247-251 (2005).
Nuffel, M. V. “Understanding probiotic yeast” (2019).
Offei, B., Vandecruys, P., De Graeve, S., Foulquié-Moreno, M. R. & Thevelein, J. M. “Unique genetic basis of the distinct antibiotic potency of high acetic acid production in the probiotic yeast Saccharomyces cerevisiae var. boulardii.” Genome Research (2019).
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