which allowed us to directly
monitor the growth of the yeast cultures with a Klett-Summerson photoelectric
colorimeter. All of the seed cultures were incubated under the same conditions
until they reached the late log phase (400 to 450 KU [OD600, 80 to 90]) and then
were stored at 4°C. The established seed cultures were transferred once a month
by transferring 2 ml of each 1-month-old seed culture to another flask containing
50 ml of sterile medium and growing the cells to a density of 400 to 450 KU.