All yeasts are eukaryotic microorganisms, which are most commonly defined as unicellular fungi. In nature, yeast species are found mainly in association with plants or animals, but are also present in soil and aquatic environments. They colonize an extremely wide range of ecosystems, both natural and in connection with human activities, mainly for their ability to grow and survive in different and stressful environments.
Saccharomyces cerevisiae is a species of yeast that has been used for centuries for a variety of processes including brewing and bread-making. More recently, yeast and yeast cell wall components have been utilized as a supplement. Live yeast products and their derivatives, such as yeast cell wall products, are currently utilized in food animal production.
Yeast products are often fed to livestock as either a live yeast (direct fed microbial), as yeast cell wall, or as a combination of the two. One of the major components of yeast and yeast cell wall products are polysaccharides such as α-d-glucan and β-d-glucan. These polysaccharides not only interact directly with immune cells, but are also able to bind bacteria to prevent attachment and colonization of pathogens in the gastrointestinal tract. In addition to pathogen fighting, yeast cell wall components may possess antioxidant and antitumor properties. From an animal health and immunity perspective, yeast cell wall components from Saccharomyces cerevisiae have been reported to promote immune cells in many species. This occurs because the glucan particles are recognized as a fungal cell wall pathogen-associated molecular particles and glucanss serve as an effective simulants for IgG antibody production.
Yeast is frequently used as a probiotic in aquaculture with the potential to substitute for antibiotics. Secretory metabolites improve gut function, relieves stress status, and reduces intestinal inflammation of Nile tilapia fed diets supplemented with baker's yeast.
Yeasts have been extensively studied because they possess many features that make them suitable as biocontrol agents. Killer toxin production has been demonstrated among many yeast genera, including Saccharomyces, Candida, Cryptococcus, Debaryomyces, Kluyveromyces, Pichia, Torulopsis, Williopsis and Zygosaccharomyces. The well-known mechanisms of the killer toxin against other fungi are the inhibition of β-glucan synthesis or hydrolysis of β-glucan in the cell wall and the interruption of cell division by blocking the DNA synthesis. The killer yeast phenomenon is raising interest due to the broad spectrum of activity against human and animal fungal and bacterial infections of yeast killer toxins and due to the recent identification of genes involved in antibiotic resistance and the lack of new antifungal agents.
- Live Yeast and Yeast Cell Wall Supplements Enhance Immune Function and Performance in Food-Producing Livestock: A Review †,‡
Paul R. Broadway, Jeffery A. Carroll,* and Nicole C. Burdick Sanchez Microorganismsv.3(3); 2015 Sep
- A Comparison of the Beneficial Effects of Live and Heat-Inactivated Baker’s Yeast on Nile Tilapia: Suggestions on the Role and Function of the Secretory Metabolites Released from the Yeast Chao Ran et al. PLoS One. 2015; 10(12): e0145448.
- Bioprotective Role of Yeasts Serena Muccilli1 and Cristina Restuccia2 Microorganisms. 2015 Dec; 3(4): 588–611.