Saccharomyces boulardii

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A Microbial Biorealm page on the genus Saccharomyces boulardii

Classification

Higher order taxa

Domain (Superkingdom): Eukaryota

Kingdom: Fungi

Subkingdom: Dikarya

Phylum: Ascomycota

Subphylum: Saccharomycotina

Class: Saccharomycetes

Order: Saccharomycetales

Family: Saccharomycetacecae

Species

NCBI: Taxonomy

Genus species: Saccharomyces boulardii

Description and significance

Saccharomyces boulardii is a tropical strain of yeast, first isolated from lychee and mangosteen fruit from Indochina in 1934 by a French scientist by the name of Henri Boulard. Saccharomyces boulardii although similar to Saccharomyces cerevisiae, differs in its non-pathogenic and biotherapeutic features. It has been found to be an effective probiotic that combats a wide range of gastrointestinal disorders and is commercially available in 90 countries around the world. (see Biotechnology). S. boulardii have been found to be non-systemic, surviving only in the gastrointestinal tract at low pH levels, and capable of growth at temperatures up to 37°C (3). Saccharomyces boulardii is used in the treatment of a variety of gastrointestinal disorders, anti-biotic-associated diarrhea, nasogastric tube-associated diarrhea, diarrhea in both children and adults, and viral-infection associated diarrhea. It has also shown to weaken the effects of microbial disease caused toxins.

S. boulardii has sparked interest around the world, specifically due to its wide variety of interactions with other microbes and ability to disable gastrointestinal disorder and diarrheal symptoms. Current research has examined the science of taxonomy, particularly examining the relationship between S. boulardii and its close relative, S. cerevisiae. Although its genomic structure is nearly 100% similar and most argue that they should be of the same species, S. boulardii possesses unique abilities which allow it to survive in the most extreme conditions. S. boulardii also has been known to secrete a variety of proteases which have inhibiting abilities on pro-inflammatory cytokines.

Genome structure

Although there has not been substantial research done on the genome structure of S. boulardii, this is partly due to the fact that it is nearly identical to that of S. cerevisiae. S. cerevisiae was the first eukaryotic genome to be completely sequenced. The completion of the genome was a result of a worldwide collaboration (23). The sequence contains 13,000,000 base pairs, 6,275 genes, 5885 of which are potential protein-encoding genes(23). Approximately 140 genes are strictly for specifying ribosomal RNA, 40 genes are for small nuclear RNA molecules and 275 function as transfer RNA genes (23). It has been observed that there is a significant amount of redundancy. Approximately 23% of the genome is identical to the human genome (23). Chromosomes possess a single linear double stranded DNA (23).

Cell structure and metabolism

S. boulardii are oval cells with thick-walled cells which are approximately 10 µm long by 5 µm wide (24). The S. boulardii cell wall makes up approximately 30% of the dry weight of the cell and is primarily composed of polysaccharides (85%) and proteins (15%) (24). Extensive biochemical analyses reveal that glucose, N-acetylglucosamine (GlcNAc), and mannose residues represent 80 to 90%, 1 to 2%, and 10 to 20% of the total polysaccharide, respectively (24).

S. boulardii is classified as an anaerobe, meaning it can grow under aerobic or anaerobic conditions( 25). Although it prefers to use glucose, it is possible to use monosaccharides, polysaccharides, oligosaccharides, ethanol, acetate, glycerol, pyruvate, and lactate. Glucose goes through the glycolytic pathway for metabolism. S. bouldardii are heterotrophes, meaning they acquire their energy from glucose (25). S. boulardii prefers fermentation over respiration 98 to 2% (25). The fermentation pathway is known as Embden-Myerof Pathway (EMP) which yields products of ethanol (25). The consumption of glucose eventually will lead to a condition known as “cell depression”, which initiates oxidation of ethanol into carbon dioxide and water. Carbon sources which are non-fermentable must enter gluconeogenesis (25).

Saccharomyces boulardii acts as a shuttle to liberate enzymes, proteins, trophic factors during its intestinal transit to improve host immune defenses, digestion, and absorption of nutrients (5). S. boulardii is able to secrete polyamines (spermine and spermidine) during the intestinal transit to regulate gene expression and in turn protein synthesis (5). S. boulardii relieves symptoms of intestinal injury and inflammation from an array of pathogens (6). In addition, S. bouldardii promotes the secretion of an antibody known as Immunoglobin A (IgA) in rat jejunum (located in small intestine). IgA’s are effective as defense to pathogenic microbes in the gastrointestinal and respiratory tracts (4).

Inflammation of the large intestine and sometimes small intestine is caused by the infiltration of T cells which aggregate in the lymph nodes. S. boulardii reduces inflammation by controlling and limiting T cell infiltration, specifically those T cells within the colon (14). Further research has suggested alternative methods of mechanism for the anti-inflammatory yeast. It was found that S. boulardii exerts anti-inflammatory effects by modulation of host cell signaling and pro-inflammatory gene expression. Specifically, the probiotic yeast is able to obstruct NF-kappaB activation and NF-kappaB-mediated IL-8 gene expression in the intestinal epithelial cells, resulting in the decrease of inflammation (6). In a separate study, researchers found that S. boulardii could also modulate the expression of PPAR-gamma. Stimulation of PPAR-gamma expression by S. boulardii results in a decrease in response of intestinal epithelial cells to proinflammatory cytokines (16).

Ecology

S. boulardii have been found to interact with a variety of microbes within the gastrointestinal tract of the human body and shown inhibitory effects on inflammation causing agents. S. boulardii have been shown to reduce the concentration of diarrhea causing agents and their associated toxins (3). All types of diarrhea are effectively remedied by S. boulardii including acute diarrhea in adults, children, and infants (22), chronic diarrhea in AIDS patients (21), and diarrhea caused by bacterial infections.

S. boulardii has been utilized as a combatant to anti-biotic associated diarrhea, specifically with patients that suffer from Clostridium difficile (13). C. difficile infection is caused by anti-biotic treatments which eradicate the natural microflora in the lining of the gut causing inflammation to the colon and diarrhea (13). S. boulardii has been found to replenish a number of microflora in the digestive tract (13). C. difficile is an anaerobe which produces two toxins (A &B) responsible for nosocomial diarrhea in adults (13). Studies have found that S. boulardii decreases levels of C. difficile, however the most prominent effect is the reduction in concentration of C. difficile produced toxins, A and B (13). S. boulardii does so by releasing a 54-kDa protease that proteolytically digests toxin A and B and their brush border membrane receptors (13). In addition, S. boulardii inhibits C. difficile growth and has the ability to stimulate host mucosal activity to enhance the intestinal mucosal immune response (13).

S. boulardii is also effective at inhibiting the effects of Cholera, a condition caused by V. cholerae, a microbe which produces toxins that activate adenylate cyclase to stimulate cyclic AMP production, causing diarrhea (3). It was found that the mechanism of action involved a secretion of a protease known as 120 kDa which decreases the concentration of cholera-toxin induced cAMP in epithelial cells by inhibiting the stimulation of adenylate cyclase (12).

S. boulardii is an effective treatment for patients with inflammatory bowel disease (IBD). IBD is characterized by the common symptoms of abdominal pain, inflammation of the large intestine, disrupted intestinal transit, constipation or diarrhea, dyspepsia, and distension. Most of these symptoms are a result of an imbalance of microflora (18). S. boulardii treatment have been found to decrease all the symptoms of IBD (18).

S. boulardii decreases the quantity and severity of lesions developed by E. histolylica (3).

S. boulardii has been found to be an effective instrument in preventing the relapse of patients with Crohn’s Disease who have already achieved remission. Also, S. boulardii have been found to be advantageous in reducing the gastrointestinal symptoms and diarrhea associated with Ulcerative Collitis (7).

S. boulardii has also been shown to fight giardiasis, a condition caused by the bacteria, Giardia lamblia which coats the interior of the small intestine, cutting off nutrient absorption (22).

S. boulardii exhibits excellent anti-microbial effects, specifically against the pathogenic bacteria known as E.coli and S. typhi which cause acute infectious diarrhea. The mode of action known as mannose-sensitive adhesion involves the binding of the pathogenic bacteria to specific sites on the surface of S. boulardii by way of lectin receptors. Because of this irreversible adhesion, pathogenic bacteria are kept from invading the brush border, and conveniently excreted (19).

Bacterial enteropathogens such as the ones above are responsible for approximately 80% of all cases of Traveler’s Diarrhea (TD). Not only has S. boulardii proved to be an effective remedy for diarrhea, but studies have shown that consumption of S. boulardii as a preventative measure (taken 5-7 days prior to departure) decreases the risk of diarrhea (20).

S. boulardii has been found to effectively treat diarrhea associated with viral infections. Among the most studied is chronic diarrhea associated with the HIV virus (AIDS). S. boulardii was given to patients with Stage IV AIDS with the establishment of a control group receiving placebos. Dramatic improvements were seen only 18 months later, including an increase in body weight (whereas the condition of patients given placebos continued to deteriorate significantly) and a decrease of gastrointestinal symptoms (21).

Pathology

Although many have classified Saccharomyces boulardii as a non-pathogenic yeast, there have been evidence that S. boulardii is capable of acting as an opportunistic pathogen, causing Saccharomyces fungemia (15). Such cases have been identified as associations to yeast infection via inserted catheters (3). Other similar species, such as the Saccharomyces cerevisiae, which is closely related to the pathogenic species, Candida is known to be an emerging opportunistic pathogen (10). It has been documented more frequently in the past decade the severity of cases of Saccharomyces fungemia, particularly with S. boulardii and S. cerevisiae (15).

Patients who suffer from yeast allergies are not suggested to consume Saccharomyces boulardii, since it has been found to cause worsened symptoms in patients with immunocompromised systems (9).

Application to Biotechnology

Saccharomyces boulardii due to its non-pathogenic and biotherapeutic characteristics have been effectively used for the treatment and prevention of gastrointestinal disorders from as early as the 1900’s. In fact, Saccharomyces boulardii was discovered when scientist Henri Boulard observed natives of Indochina eating the skin of lychee and mangosteen fruit to control and remedy the effects of cholera, a severe diarrheal disease. S. boulardii was first isolated in 1934. Its probiotic effects were first seen in France during the 1950s. In 1953, a French biotech company, Biocodex Laboratories (Montrouge, France) commercially developed S. boulardii in a lyophilized form (patented dehydration process) primarily as treatment for antibiotic-associated diarrhea (3). Today, it is commercially available in over 90 countries in Europe, South America, and Africa. S. boulardii has been marketed under a variety of different names- in France, S. boulardii is found under the name, Ultra-Levure (http://www.biocodex.com/produits/index.php) and in the UK, S. boulardii is known as Diarsafe (http://www.dtecta.co.uk/diarsafe.html). Currently in the United States, S. boulardii awaits approval as it undergoes investigational phase III clinical studies by the Food and Drug Administration (FDA) (3).

Current Research

S. boulardii has proven to be an effective non-pathogenic and biotherapeutic agent. However, recently, there has been a record of invasive infections from S. boulardii, specifically Ultra-Levure- the French label. This raises great concern since the probiotic has been made commercially available in many countries. Current studies have focused on the prospect of S. boulardii’s ability to become an opportunistic pathogen (3), meanwhile many researchers and biotechnology companies are also in the works for developing and improving the probiotic to combat gastrointestinal disorders, diarrhea, cancer, and surgical infections (28). Potential uses of the probiotic could be revolutionary, but most importantly efforts are needed to improve knowledge of probiotics, specifically their mechanisms of action, as well as determine why, how, and when they fail (27).

With improvements in techonological techniques, methods, and equipment, current research has also focused on improving the science of taxonomy. Doing so includes the construction of phylogenetic trees based on DNA sequencing of genes. These trees are intended to provide some kind of insight into evoluationary history, reduce ambiguity between classification of microorganisms, for example distinguishing a closely related- perhaps identical species as we observe with the S. boulardii and the S. cerevisiae (26).

Initially classified as a separate species from Saccharomyces cerevisiae, recent research and publications have challenged the legitimacy of its taxonomic classification, contending that S. boulardii and S. cerevisiae belong in the same species (2). A recent investigation using a variety of diagnostic tools including CHEF karyotyping and hybridization, Ty fingerprinting, and micro array hybridization genome comparison were used to determine the relationship between Saccharomyces boulardii and Saccharomyces cerevisiae (3). Based on comparative genomic hybridizations for whole-genome analysis, comparison of DNA sequencing of specific genes (SRB1/PSA1, PKC1, CHS1, CHS3; mitochondrial genes COX2 and COX3) concluded that S. boulardii and S. cerevisiae do in fact, belong to the same species (2). Sequences of D1/D2 domain of the 26S rDNA were 100% identical. Sequence analysis of the mitochondrial cytochrome-c oxidase II gene (COX2) yielded 100% identical sequences. Electrophoretic karyotypes appeared identical suggesting that S. boulardii should not be recognized as a separate species (17).

In a more recent study, done in 2007, it was revealed that Saccharomyces boulardii differed significantly from Saccharomyces cerevisiae. Specifically, there are differences in copy numbers of genes in the subtelomeric regions as well as its yeast retrotransposons (2). Overall differences occurred at both genomic and physiological levels, particularly with sporulation, individual chromosome and gene copy numbers, ability for pseudo switching, and survival at low acidic levels, the latter two features having a direct bearing on the probiotic nature of Saccharomyces boulardii (2).

References

1. ”Saccharomyces boulardii”. NCBI Taxonomy Browser. 25 August 2007.

2. Edwards-Ingram, L., Gitsham, P., Burton, N., Warhurst, G., Clarke, I., Hoyle, D., Oliver, S. G., and Stateva, L. (2007). “Genotypic and Physiological Characterization of Saccharomyces boulardii, the Probiotic Strain of Saccharomyces cerevisiae”. Appl Environ Microbiol. 2007 April; 73(8): 2458–2467.

3. McFarland, L., Bernasconi, P. (1993). "Saccharomyces boulardii: a review of an innovative biotherapeutic agent". Microb Ecol Health Dis. 6: 157–71.

4. Qamar, A., Aboudola, S., Warny, M., Michetti, P., Pothoulakis, C., LaMont, J.T., and Kelly, C.P. (2001). “Saccharomyces boulardii Stimulates Intestinal Immunoglobulin A Immune Response to Clostridium difficile Toxin A in Mice”. Infect Immun. 2001 April; 69(4): 2762–2765.

5. Buts, J.P., and De Keyser, N. (2006). Digestive Diseases & Science. 51(8):1485-92. E-Pub 2006 Jul 13.

6. Sougioultzis, S., Simeonidis, S., Bhaskar, K.R., Chen, X., Anton, P.M., Keates, S., Pothoulakis, C., Kelly, C.P. (2006) Biochemical Biophysical Research Communications. 2006 Apr 28; 343(1):69-76. E-Pub 2006 Feb 23.

7. Guslandi, M., Mezzi, G., Sorghi, M., Testoni, P.A. (2000 Jul). “Saccharomyces boulardii in maintenance treatment of Crohn's disease”. Digestive Disease & Sciences. 45(7): 1462–4

8. McFarland, L. (2005). “Can Saccharomyces boulardii prevent antibiotic-associated diarrhea in children?” Nature Clinical Practice Gastroenterology & Hepatology. (2005) 2, 262-263

9. Muñoz, P. (2005). "Saccharomyces cerevisiae Fungemia: An Emerging Infectious Disease". Clinical Infectious Diseases. 40: 1625–1634.

10. Goldstein, A.L., and McCusker, J.H. (2001). “Development of Saccharomyces cerevisiae as a Model Pathogen: A System for Genetic Identification of Gene Products Required for Survival in the Mammalian Host Environment”. Genetics. Vol. 159, 499-513.

11. Czerucka, D., and Rampal, P. (1999). "Effect of Saccharomyces boulardii on cAMP-and2+-dependent C1-secretion in T84 cells". Digestive Diseases and Sciences 44: 2359–68.

12. Czerucka, D., Nano, J.L., Roux, I., Bernasconi, P., and Rampal, P. (1993). “The cholera toxin neutralizing factor secreted by Sacchromyces boulardii acts directly on cells”. Abstract No. 1087. Gastroenterology. 102, A207.

13. Castagliuolo, I., Riegler, M.F., Valenick, L., LaMont, J.T., and Pothoulakis, C. (1999). “Saccharomyces boulardii Protease Inhibits the Effects of Clostridium difficile Toxins A and B in Human Colonic Mucosa”. Infect Immun. 1999 January; 67(1): 302–307.

14. Dalmasso, G., Cottrez, F., Imbert, V., Lagadec, P., Peyron, J.F., Rampal, P., Czerucka, D., Groux, H., Foussat, A., Brun, V. (2006). “Saccharomyces boulardii inhibits inflammatory bowel disease by trapping T cells in mesenteric lymph nodes”. Gastroenterology. 2006 Dec;131(6):1812-25.

15. Lherm, T., Monet, C., Nougière, B., Soulier, M., Larbi, D., Le Gall, C., Caen, D., Malbrunot, C. (2002). “Seven cases of fungemia with Saccharomyces boulardii in critically ill patients”. Intensive Care Medicine. 2002 Jun; 28 (6):1432-1238.

16. Lee, S.K., Kim, H.J., Chi, S.G., Jang, J.Y., Nam, K.D., Kim, N.H., Joo, K.R., Dong, S.H., Kim, B.H., Chang, Y.W., Lee, J.I., Chang, R. (2005). “Saccharomyces boulardii activates expression of peroxisome proliferator-activated receptor-gamma in HT-29 cells”. Korean Gastroenterology. 2005 May; 45(5):328-34.

17. Van der Aa Kühle, A., Jespersen, L. (2003). “The taxonomic position of Saccharomyces boulardii as evaluated by sequence analysis of the D1/D2 domain of 26S rDNA, the ITS1-5.8S rDNA-ITS2 region and the mitochondrial cytochrome-c oxidase II gene”. Systematic & Applied Microbiology. 2003 Nov; 26(4):564-71.

18. Maupas, J., Champemont, P., Delforge, M. (1983). "Treatment of irritable bowel syndrome with Saccharomyces boulardii: a double blind, placebo controlled study". Medicine Chirurgie Digestives. 12(1): 77–9.