From biofuels to fish food to gold nanoparticles, Yarrowia lipolytica is all the rage these days as a powerful workhorse for biotechnology. But this yeast also has important roles in the flavor development and appearance of some traditional fermented foods. Here’s all you need to know about this versatile and beautiful yeast.
Macro- and microscopic appearance:
Yarrowia produces some of the most gorgeous microbial colonies I’ve ever seen (sorry Zygosaccharomyces!). When plated out on standard lab media, Yarrowia usually doesn’t make typical smooth and round yeast colonies like most Saccharomyces yeast strains. Instead, it makes colonies with ridges, wrinkles, or uneven mounds that tend to be fuzzy in appearance (left figure below). At a microscopic level, cells of Yarrowia are a mix of typical yeast-like cells (small round cirles) as well as filamentous cells (long tubes in right photo in panel below). This mix of yeast-like and mold-like cells is characteristic of so-called dimorphic fungi, where resources and other environmental conditions can affect how yeasty or moldy a fungus appears.
There aren’t any consistent tell-tale macroscopic signs that you have a patch of Yarrowia growing on your cheese, but beige and compactly fuzzy spots (like those shown above) are good spots to check.
Yarrowia can tolerate a fairly wide range of conditions, allowing it to grow in diverse environments, from kerosene aviation fuel to the “fingernail of 49-year-old woman in Austria.” One of the most common food habitats for Yarrowia is the dairy environment. I commonly find this yeast in samples of raw milk (probably originating from the cow itself) and in raw milk cheeses, but it has also been reported in many other fermented foods including other fermented dairy products (yogurts, butters, etc.), fermented sausages, and less frequently in grain ferments such as sourdough and tempeh. If you are hunting for this yeast on cheeses, try bloomy rind goat cheeses or washed rind cheeses like Livarot.
Yarrowia lipolytica can tolerate fairly high salt concentrations (up to 12% salt), a range of acidity (from pH 2.5 to pH 8), and really enjoys high fat and high protein environments, such as meats and dairy products. It can also grow in pretty chilly conditions, from 0°C to 30°C (optimum temperature range is ~15 to 24°C), making it ideal for growth in cold aging and refrigeration environments. Unlike many other yeasts that can tolerate low-oxygen environments, Yarrowia lipolytica needs oxygen in order to grow. That means you’ll usually only find this yeast growing on the surface of fermented foods, like the rinds of cheeses, and not in the interior of these foods where oxygen levels are low.
Yarrowia lipolytica and other closely related species have also been reported as a spoilage yeasts, causing undesirable changes to the properties of poultry, fruit products such as juices, and fatty dressings such as mayonnaise.
Yarrowia lipolytica releases a lot of enzymes into its environment, and its especially good at chomping up proteins and fats. This process of decomposition releases nutrients that the yeast can use for itself as well as neighboring microbes. Byproducts of protein and fat decomposition can also lead to the release of aroma compounds. When we are growing Yarrowia in my lab, you can really smell it! This yeast is one of the most potent of cheese yeasts, producing a whole bouquet of sulfur compounds. It’s been demonstrated to be much more potent than many other surface-ripening yeasts such as Debaryomyces hansenii of Kluveromyces lactis.
In addition to artisan foods, this yeast is being widely used for food and chemical production. Because Yarrowia is so great at producing and releasing enzymes, it is used as a protein secretion powerhouse in biotech. Genes that encode for useful proteins are often spliced into the yeast, and it is used to efficiently produce and secrete these proteins in large batches. Because the yeast produces so much oil within its cells, there is great interest in using it for biofuels production. Seafood producers are also interested in how fishmeal supplemented with Yarrowia could replace the need for wild-caught fish as a food source in commercial fish production.
Article by Benjamin Wolfe
For more detailed info on Yarrowia, check out the following research papers:
Mansour, S. et al. 2008. Lactate and amino acid catabolism in the cheese-ripening yeast Yarrowia lipolytica. Applied and Environmental Microbiology 74: 6505-6512
Groenewald, M. et al. 2014. Yarrowia lipolytica: Safety assessment of an oleaginous yeast with a great industrial potential. Critical Reviews in Microbiology 40:187-206