Another beneficial cell modification is the adjustment of substrate and growth requirements of a cell. By changing cell needs, the raw material cost, equipment expenses, and skill required to grow and maintain cell cultures can be significantly reduced. For example, scientists have used foreign enzymes to engineer a common industrial yeast strain which allows the cells to grow on substrate cheaper than the traditional glucose. Because of the biological engineering focus on improving scale-up costs, research in this area is largely focused on the ability of various enzymes to metabolize low-cost substrates.