Relationship Between Cell Size and Efficiency of Synchronization During Nitrogen-Limited Phased Cultivation of Candida utilis

Abstract

Under the phased method of cultivation the yeast Candida utilis grew and divided synchronously. The newly formed cells were relatively small, and a new cell cycle was not initiated until the cells could attain a certain minimum size (critical size). Although the cells expanded to some extent after division, the critical size was not reached until a fresh supply of medium was provided. With the arrival of the fresh supply of growth medium at the beginning of the phasing period, the cells expanded rapidly, and new cell cycles were initiated. The cells continued to expand until the growth-limiting nutrient (nitrogen source) was exhausted or until 90 min, which ever occurred first. Usually, buds emerged at a constant time after the start of the phasing period. The time of bud emergence was independent of the size attained by the cells during the expansion phase of growth. The results indicated that it was initiation of the cell cycle that was under size control, and not bud emergence. Bud emergence seemed to be under the control of a timer. The start of this timer seemed to be at or immediately after the beginning of the phasing period. Protein synthesis was essential for the initiation and expansion of buds. However, inhibition of protein synthesis by cycloheximide did not prevent unbudded cells or the parent portion of budded cells from expanding. Cycloheximide seemed to abolish the control mechanism(s) which prevented the cells from expanding after they had reached the maximum size.

Improvement of Omega-3 Docosahexaenoic Acid Production by Marine Dinoflagellate Crypthecodinium cohnii Using Rapeseed Meal Hydrolysate and Waste Molasses as Feedstock

“…cohnii grew vitally on RMH-molasses medium as the cells were dominantly small and full of high electron density material in cytosol (Fig 7C and 7D ). This is common that environmental change of nitrogen supply affects the cell size of microorganisms including bacteria, yeast and algae [ 46 – 48 ].…”

Effect of pH on the rate of Candida utilis cell cycle initiation

“…The earliest visible indication that the cell has entered the deterministic phase is bud initiation, which in C. utilis and S. cerevisiae occurs at the same time as the initiation of DNA synthesis (13,17). We reported earlier that cell cycle initiation in C. utilis occurs a constant time before bud emergence (18). Thus, bud emergence is under the control of a timer, and the start of this timer is at the beginning of the cell cycle.…”

“…In previous studies (17,18), the yeast C. utilis was grown under the phased method of cultiva-tion without controlling the pH. However, some control was exerted on the pH of the culture by the internal buffering action of 20 mM phosphate in the growth medium.…”