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

Veronika Kselíková,Kateřina Bišová,Vilém Zachleder

doi:10.3390/biom11060861

Abstract

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 Chlamydomonas reinhardtii, a well-established model organism in cell cycle studies, are no exception. Chlamydomonas reinhardtii, a green unicellular alga of the Chlorophyceae 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 C. reinhardtii. Synchronous cultures of C. reinhardtii were cultivated in growth medium containing 70 or 90% D2O. We characterize specific deuterium-induced shifts in attainment of commitment points during growth and/or division of C. reinhardtii, 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.

Highlights

Deuterium (2 H or D) is a stable isotope of hydrogen with a natural abundance of0.015% [1]
As deuterium exhibits the largest relative increase in atomic mass compared to its lighter isotope protium, it exhibits the strongest kinetic isotope effect observable among stable isotopes of biogenic elements [3]
Cells were synchronized by alternating light/dark regimes prior to the experiment and grown in continuous light for one cell cycle, i.e., from their birth until completion of cell division

Summary

Introduction

Deuterium (2 H or D) is a stable isotope of hydrogen with a natural abundance of0.015% [1]. The biggest and only difference between the atomic structures of deuterium and protium (1 H) is the extra neutron in the deuterium nucleus. This change in the atomic structure results in unprecedented consequences in its physico-chemical characteristics. Heavier isotopes generally exhibit slower reaction rates, with the phenomenon being described as the kinetic isotope effect. This effect is normally very low [2], but not so with deuterium. Exposing living organisms to stable isotopes of other biogenic elements (13 C, 15 N, 17 O or 18 O) has little or no effect [3]; their exposure to deuterium results in various physiological and morphological aberrations

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Conclusion