To Divide or Not to Divide? How Deuterium Affects Growth and Division of .

Extensive in vivo replacement of hydrogen by deuterium, a stable isotope of hydrogen, induces a distinct stress response, reduces cell growth and impairs cell division in various organisms. Microalgae, including , a well-established model organism in cell cycle studies, are no exception. , a green unicellular alga of the class, divides by multiple fission, grows autotrophically and can be synchronized by alternating light/dark regimes; this makes it a model of first choice to discriminate the effect of deuterium on growth and/or division. Here, we investigate the effects of high doses of deuterium on cell cycle progression in . Synchronous cultures of were cultivated in growth medium containing 70 or 90% DO. We characterize specific deuterium-induced shifts in attainment of commitment points during growth and/or division of , contradicting the role of the "sizer" in regulating the cell cycle. Consequently, impaired cell cycle progression in deuterated cultures causes (over)accumulation of starch and lipids, suggesting a promising potential for microalgae to produce deuterated organic compounds.