Saccharomyces turicensis

Other Names

Kazachstania turicensisMaudiozyma turicensisS. turicensisSaccharomyces intermedius var. turicensis

Synopsis

Saccharomyces turicensis (syn. Kazachstania turicensis / Maudiozyma turicensis)

1. Identity, Nomenclature, and Taxonomy

Saccharomyces turicensis is an ascomycetous yeast first described as a new species in 1999 by Wyder, Meile, and Teuber. The species was formally described from isolates obtained from different kefir grains. The name Saccharomyces turicensis was proposed to indicate the place of isolation — Zürich, whose Latin name is Turicum.

The organism has undergone several taxonomic revisions since its original description. In 2003, Kurtzman transferred the species to the genus Kazachstania, establishing the combination Kazachstania turicensis (Wyder, Meile & Teuber) Kurtzman comb. nov., with the basionym Saccharomyces turicensis Wyder, Meile & Teuber. Most recently, the NCBI taxonomy database reflects a further reclassification: the organism is now placed as Maudiozyma turicensis (Wyder, Meile & Teuber) Q.M. Wang, Yurkov & Boekhout, 2024, within the family Saccharomycetaceae, order Saccharomycetales, class Saccharomycetes, subphylum Saccharomycotina, and phylum Ascomycota. All three names — Saccharomyces turicensis, Kazachstania turicensis, and Maudiozyma turicensis — refer to the same organism and appear interchangeably in the scientific literature, with Kazachstania turicensis being the most common name in recent peer-reviewed research.

Kazachstania species are ubiquitous yeasts belonging to the Saccharomycetaceae family. At the time of its original description, the morphological properties of S. turicensis differed from related species, though its physiological characteristics came close to those of Saccharomyces bayanus Saccardo and Saccharomyces pastorianus Reess ex E.C. Hansen. Electrophoretic karyotyping and restriction fragment length polymorphism (RFLP) of the internal transcribed spacer (ITS) region, however, yielded clear differences from those species; sequences of the D2 domain at the 5′-terminal end of the large subunit ribosomal RNA gene revealed 98.0% identity with Saccharomyces exiguus. Since strains of a particular yeast species usually show less than 1% substitution in the D2 domain, the yeast was considered to represent a new species.

Common Names and Synonymy

Valid basionym: Saccharomyces turicensis Wyder, Meile & Teuber (1999)
Transferred name: Kazachstania turicensis (Wyder, Meile & Teuber) Kurtzman (2003)
Most recent reclassification: Maudiozyma turicensis (Wyder, Meile & Teuber) Q.M. Wang, Yurkov & Boekhout (2024)
Common informal designation: "kefir yeast"

2. Natural Sources and Occurrence

Saccharomyces turicensis is primarily isolated from kefir grains — the polysaccharide-protein matrices used to ferment kefir. The microbiota of kefir grain samples from diverse geographic regions contains Kazachstania turicensis, regardless of the region of isolation; it is a former species of Saccharomyces sp. often isolated from different kefir grains and mentioned in the works of Chinese scientists. This yeast has been identified in kefir grain samples from Asia, Europe, North America, and the Caucasus region.

Using a combination of conventional microbiological cultivation and PCR-DGGE, four yeast species were identified from kefir cultures in Taiwan; specifically, Kluyveromyces marxianus, Saccharomyces turicensis, and Pichia fermentans were found in Taiwanese kefir grains with 76%, 22%, and 2% distribution, respectively.

Studies employing high-throughput amplicon sequencing found that the fungal communities of kefir grains were dominated by Kazachstania turicensis and Torulaspora delbrueckii, although the ratio between the two varied significantly; these findings suggest that the microbial communities in kefir grains change over time.

Sequencing-based studies have shown that proportions of Kazachstania exceeded 50% in 11 of the kefir grain samples and in 13 of the fermented milk samples analysed, while being comparatively low in other samples, highlighting substantial geographic and sample-to-sample variability.

Beyond kefir, the species has also been documented in dietary supplement formulations. One commercial probiotic fermentation technology (PFT) kefir product has been described as containing, among other components, the yeast strains Kazachstania turicensis, Kazachstania unispora, and Kluyveromyces marxianus at approximately 2–3% of the mixture.

3. Traditional and Historical Use

Saccharomyces turicensis does not have a documented history of use as an isolated ingredient in traditional medicine systems. Its historical relevance is entirely embedded within the broader context of kefir, a fermented dairy beverage with deep roots in Caucasian and Central Asian tradition.

Traditionally, kefir fermentation was initiated through the addition of kefir grains, which originally formed during the fermentation of milk, to unfermented milk in a sheep or goat skin bag. The name kefir is derived from the Turkish word keyif, meaning "good feeling" for the feelings experienced after drinking it. One of the features that distinguishes kefir from many other fermented dairy products is the requirement for the presence of a kefir grain in fermentation and the presence and importance of a large population of yeasts.

S. turicensis was not isolated or characterised as a discrete species until 1999; its identity as a distinct microorganism was therefore unknown to traditional practitioners who consumed or prepared kefir. The yeast's contribution to kefir's historically attributed properties — such as digestive comfort, general wellness, and preservation of milk — was indistinguishable from the combined activity of the complex microbial community within kefir grains. No traditional preparation specifically targeting this yeast has been identified in the ethnobotanical or ethnomycological literature.

4. Occurrence in Kefir Grain Structure and Fermentation

Kefir grains play a natural starter culture role during the production of kefir and are recovered after the fermentation process by milk straining; these grains are composed of microorganisms immobilised on a polysaccharide and protein matrix, where several species of bacteria and yeast coexist in symbiotic association.

A particularly significant aspect of S. turicensis biology is its proposed role in the very formation of kefir grains. According to a hypothesis based on microstructural examination, Lactobacillus kefiranofaciens and Saccharomyces turicensis start to auto-aggregate and co-aggregate into small granules, with aggregation enhanced as pH drops; biofilm producers including Lactobacillus kefiri, Kluyveromyces marxianus HY1, and Pichia fermentans HY3 then adhere to the surface due to their cell surface properties, after which the kefir yeasts and Lactobacillus continue to co-aggregate with the granule strains to become a three-dimensional microcolony.

Although kefir yeasts produce metabolites that contribute to desirable and typical kefir sensory properties, they are less studied than kefir bacteria. The non-lactose fermenting yeasts of kefir include Saccharomyces cerevisiae, Torulaspora delbrueckii, Pichia fermentans, Kazachstania unispora, Saccharomyces turicensis, Issatchenkia orientalis, and Debaryomyces occidentalis. The complex interactions between yeast and bacteria and their interdependence in kefir grains are not completely understood; however, when bacteria are separated from the grain, yeast will not grow as efficiently.

Kazachstania is a non-Saccharomyces yeast that can assimilate lactic acid and hydrolyse glucuronide to provide metabolic substrates for heterofermentative lactic acid bacteria, enabling them to produce acetic acid from fructose.

In one fermentation technology study, Saccharomyces turicensis was one of the kefir yeasts successfully entrapped in microspheres along with lactic acid bacteria for use as an immobilised starter culture, using an entrapment ratio based on the distribution of these organisms in kefir grains.

5. Key Constituents and Mechanisms of Action

As a yeast organism, S. turicensis does not have discrete "active constituents" in the phytochemical sense that would apply to a plant extract. Its biological relevance derives from its cellular components and metabolic activities. The following constituents and activities are attributable to Kazachstania/Saccharomyces turicensis based on published research:

Cell wall polysaccharides (β-glucans and mannoproteins): Like other ascomycetous yeasts, S. turicensis possesses a cell wall composed primarily of β-1,3-glucan, β-1,6-glucan, chitin, and mannoproteins. These structures are known to interact with pattern recognition receptors of the innate immune system, such as Dectin-1, and are recognised as general features of probiotic yeasts.
Immunomodulatory effects: Oral administration of K. turicensis CAU Y1706 suppressed T helper type 2 (Th2) immune response factors by regulatory T cells and upregulated T helper type 1 (Th1) cytokine levels. It also reduced immunoglobulin E (IgE) levels as well as the number of eosinophils and mast cells. This Th1/Th2 rebalancing effect is a recognised probiotic mechanism relevant to allergic diseases.
Gut microbiota modulation: Faeces from K. turicensis CAU Y1706-treated mice had more butyrate-producing bacteria including Lactobacillus, Bacteroides, Ruminococcus, and Akkermansia, indicating that the yeast modulates immune responses as well as gut microbiota.
Lactic acid assimilation: The ability of Kazachstania to assimilate lactic acid and hydrolyse glucuronide provides metabolic substrates for heterofermentative lactic acid bacteria. This metabolic cross-feeding activity supports the broader ecology of fermentation communities.
Fermentation metabolites: As a non-lactose-fermenting kefir yeast, S. turicensis contributes ethanol, carbon dioxide, and other metabolic end-products to the kefir beverage. CO₂ and alcohol, formed as a result of yeast metabolic activities, are the most important yeast-derived components of kefir; the kefir microbiota collectively produces lactic acid, CO₂, small amounts of alcohol, acetaldehyde, acetone, and diacetyl, contributing to kefir's unique aroma and consistency.

6. Scientific Evidence by Area of Use

6.1 Atopic Dermatitis (Allergic Skin Inflammation) — Animal Evidence

The most substantive body of direct research on K. turicensis as an isolated probiotic agent concerns atopic dermatitis (AD). Atopic dermatitis is a chronic inflammatory skin disease that results in considerable economic and social burden; prior to this line of research, the effects of probiotic yeast specifically on AD had not been investigated.

Researchers isolated Kazachstania turicensis CAU Y1706, characterised as a kefir yeast, and evaluated its mitigating effects using an ovalbumin (OVA)-sensitised AD mouse model. Key findings from this preclinical study include:

Overall, K. turicensis CAU Y1706 was generally effective against AD; oral administration suppressed Th2 immune response factors via regulatory T cells and upregulated Th1 cytokine levels.
The yeast reduced IgE levels as well as the number of eosinophils and mast cells; faeces from treated mice had higher proportions of butyrate-producing bacteria including Lactobacillus, Bacteroides, Ruminococcus, and Akkermansia.
K. turicensis CAU Y1706 modulates immune responses as well as gut microbiota, indicating potential for application as a supplement for alleviation of AD.

The mechanistic pathway proposed by the authors operates through the gut–skin axis: the yeast modulates gut microbial ecology and immune signalling, which in turn affects cutaneous inflammatory responses. The strain used in this research, CAU Y1706, was subsequently patented. The novel Kazachstania turicensis strain isolated and identified was deposited at the Korea Research Institute of Bioscience and Biotechnology Biological Resources Center (KCTC) on January 22, 2019 (Accession number: KCTC13794BP).

Evidence strength: Preliminary/preclinical (animal model only). All direct evidence for K. turicensis CAU Y1706 as an intervention for AD derives from a single mouse model study. No randomised controlled trials in humans have been published for this specific strain or species in relation to atopic dermatitis.

6.2 Gut Microbiota Modulation

Kazachstania is a non-Saccharomyces yeast that can assimilate lactic acid and hydrolyse glucuronide to provide metabolic substrates for heterofermentative lactic acid bacteria, enabling them to produce acetic acid from fructose; Kazachstania has also been shown to exhibit some probiotic properties. The gut microbiota-modulating effects observed in the AD mouse study — specifically the enrichment of butyrate-producing bacteria — suggest a prebiotic-like or indirect microbiome-modulatory mechanism.

Evidence strength: Preliminary/preclinical. Gut microbiota effects have been demonstrated in animal models only.

6.3 Kefir-Related Health Benefits

S. turicensis is a constituent of whole kefir, a beverage with a broader body of research supporting various health claims. Emerging evidence from in vitro, animal, and human studies suggests that kefir exerts multiple health-promoting effects, including gastrointestinal protection, anti-inflammatory, immunomodulatory, antimicrobial, antiallergic, and anti-arthritic activities. However, these effects are attributed to the complex whole-community composition of kefir, not to S. turicensis specifically, and it is not possible to isolate the yeast's unique contribution from these multi-organism intervention studies.

Evidence strength: Not directly applicable. Health evidence for whole kefir cannot be attributed specifically to S. turicensis.

6.4 Cognitive Impairment — Combination Product Evidence

One animal study investigated a kefir-derived combination product (Probiotics Fermentation Technology, or PFT) containing multiple organisms including K. turicensis in the context of streptozotocin-induced sporadic Alzheimer's disease in mice. The PFT kefir grain product is a mixture primarily (~90%) consisting of a heat-killed freeze-dried form of Lactobacillus kefiri P-IF; PFT also contains approximately 2–3% of a bacterial strain (L. kefiri P-B1) and the yeast strains Kazachstania turicensis, Kazachstania unispora, and Kluyveromyces marxianus. Given the multi-component nature of the product and the minor proportion of K. turicensis within it, no conclusions can be drawn about the specific contribution of this yeast to any outcomes.

Evidence strength: Inapplicable to this species in isolation; preliminary/preclinical for the combination product.

7. Body Systems and Health Areas of Association

Based on published peer-reviewed sources, S. turicensis / K. turicensis has been studied or discussed in relation to the following body systems:

Immune system: Th1/Th2 balance, IgE regulation, mast cell and eosinophil suppression — demonstrated in animal models.
Integumentary system (skin): Atopic dermatitis, mediated through the gut–skin axis — demonstrated in animal models.
Gastrointestinal system: Gut microbiota modulation, lactic acid metabolism, enrichment of butyrate-producing bacteria — demonstrated in animal models and mechanistic studies.
General probiotic activity: As a kefir grain constituent, associated with the broader gastrointestinal and immunological effects attributed to kefir fermentation.

8. Dosage Forms and Reported Dosages

S. turicensis / K. turicensis has not been standardised as a standalone dietary supplement with defined dosage guidelines. The published research reports the following:

In animal research: The atopic dermatitis mouse study employed strain CAU Y1706, administered orally, but the specific colony-forming unit (CFU) dose used has not been made available in the abstract-level data accessible from the published study.
In kefir products: The yeast is found consistently in kefir grains from samples across geographic regions. In traditional kefir preparation, modern kefir is made by adding kefir grains to milk typically at a proportion of 2–5% grains-to-milk. The specific viable counts of S. turicensis in the final fermented beverage vary considerably depending on fermentation conditions, origin of the grain, and grain-to-milk ratio.
In the PFT combination product: Kazachstania turicensis constitutes approximately 2–3% of the total PFT kefir grain product.

No established human clinical dosage exists for S. turicensis or K. turicensis administered as a purified or isolated supplement. No pharmacopoeial monograph (e.g., European Pharmacopoeia, USP, or WHO monograph) has been published for this species.

9. Safety Considerations

9.1 General Safety in Healthy Individuals

S. turicensis has been consumed as part of kefir by human populations for many centuries without documented adverse effects attributable to this specific yeast. As a component of a traditional fermented food, it is generally considered safe in the context of normal kefir consumption for healthy individuals. No clinical trials assessing the safety of isolated S. turicensis supplementation in humans have been published.

9.2 Opportunistic Pathogenicity in Immunocompromised Individuals

The genus Kazachstania has come under scrutiny as a source of rare opportunistic fungal infections. The emergence of rare fungal infections caused by Kazachstania spp. might be explained by the increasing number of patients with immunocompromised conditions and gastroesophageal diseases; the incidence of invasive fungal infections has increased over the past two decades, mostly associated with candidemia, and rare fungal pathogens have also emerged as agents causing such infections, notably in immunocompromised persons.

Analysis of 13 cases of fungal infections caused by Kazachstania (Arxiozyma) spp. at a university hospital in Strasbourg, France, found that among the cases, 4 patients had proven fungal disease (3 cases of invasive fungal disease and 1 mucocutaneous infection) and 9 were colonised; Candida albicans was also isolated from 11 of the 13 patients. Emergence might be associated with increasing immunocompromised conditions and gastroesophageal diseases.

While these reports involve primarily other Kazachstania species such as K. slooffiae and K. bovina, and not K. turicensis specifically, they illustrate a genus-level safety concern. A case of Kazachstania slooffiae fungemia has been documented in a 77-year-old immunocompromised male with gastrointestinal abnormalities including achalasia, gastroparesis, and prior esophagectomy, who presented with sepsis, gastric ischemia, and pleural effusion. This case, like others in the genus, occurred in a severely immunocompromised patient with pre-existing gastrointestinal pathology.

9.3 Taxonomic Misidentification Risk

High-throughput sequencing studies have noted that the reclassification of Naumovozyma and Kazachstania is relevant to interpreting kefir microbiology literature; previous studies suggested that Saccharomyces cerevisiae is common in kefir, but sequencing found the genus in only trace amounts, suggesting possible misassignment in earlier culture-based studies. This means that older safety or efficacy data attributed to "S. cerevisiae" in kefir may sometimes reflect the activity of organisms now reclassified as K. turicensis, and vice versa.

9.4 Drug and Supplement Interactions

No specific drug interaction studies for S. turicensis / K. turicensis have been published. As a yeast-based organism with immunomodulatory properties (observed in animal models), theoretical caution is warranted when considering co-administration with immunosuppressive therapy, though no human evidence documents this interaction. The antibiotic-resistance profile of this yeast is not systematically documented in the available literature, which is notable given that yeast-based probiotics are sometimes used alongside antibiotic therapy specifically because they are unaffected by antibacterial agents.

10. Summary of Evidence Limitations

The scientific literature on Saccharomyces turicensis / Kazachstania turicensis as a discrete dietary supplement or probiotic ingredient is very early-stage and limited. The key limitations are:

The only controlled study directly testing the isolated organism as a probiotic (the AD mouse study) is a single preclinical animal study with no published human replication.
Most evidence for the health effects of this yeast is embedded in whole-kefir literature, making it impossible to isolate its specific contribution from that of the broader microbial community.
No standardised dosage, clinical indication, or regulatory approval for isolated S. turicensis supplementation has been established in any jurisdiction.
No systematic reviews or meta-analyses of K. turicensis as an isolated ingredient have been published.
The genus Kazachstania contains species with documented, if rare, opportunistic pathogenic potential in immunocompromised hosts, a safety consideration that requires species-level and strain-level evaluation before clinical use of isolated preparations.

References

Health Conditions

Health conditions that Saccharomyces turicensis may help support.

No conditions available.

Body Systems

Body systems that Saccharomyces turicensis may help support.

No body systems available.