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Monitoring Saccharomyces Cerevisiea Growth with Bright Field Microscopy in Real Time

Yeast are single celled eukaryotic fungi organisms that reproduce asexually by budding or division (Figure 1). While yeast can vary in size, they typically measure 3-8 μm in diameter. Saccharomyces cerevisiea is the most commonly used strain in scientific research, baking and fermentation and has become synonymous with the term yeast.

When cultured in a fixed environment yeast cells follow a very predictable pattern of growth that can easily be divided into four phases: (1) lag; (2) log; (3) deceleration; and (4) stationary. During the lag phase, no growth occurs as newly introduced yeast mature and acclimate to the environment. This is followed by the log phase, where cells are rapidly growing and dividing. Nutrients are in excess relative to cell number and waste is being sufficiently diluted as to be insignificant. The growth rate in this phase will follow first order kinetics. As cell numbers increase cell growth begins to slow as a number of parameters (e. g. substrate and waste), each with saturation effects, become significant. Eventually the yeast cells reach the stationary phase, where no growth occurs due to high waste concentration or complete substrate consumption (Figure 2). Unfortunately these different stages make interpretation of growth data difficult. Growth rates in a static environment are a function of not only the ability of the yeast cell to grow, but also environmental conditions such depletion of nutrients or the accumulation of waste byproducts. Using a perfusion system allows for the maintenance of proper growth nutrients as well as elimination of waste products as they are produced, with growth only limited by physical space.