Novel mechanism cells use to survive dehydration
20 Jul 2016
Cihan Erkut, Vamshidhar R Gade, Sunil Laxman, Teymuras V Kurzchalia
Max Planck Institute of Molecular Cell Biology and Genetics, Germany; Institute for Stem Cell Biology and Regenerative Medicine, India
Published April 19, 2016
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Many organisms can survive losing all the water from their body in periods of severe drought by suspending their life. This ability is called anhydrobiosis (from the Greek for ‘life without water’). When the desiccated organisms encounter water again, they resume life as normal. Two organisms commonly used in research, a roundworm called Caenorhabditis elegans and a yeast called Saccharomyces cerevisiae, are anhydrobiotes.
To survive without water, anhydrobiotes alter the chemical reactions that sustain their life, and so change their metabolic state. The organisms also produce molecules that preserve the structure of their cells. One such essential molecule is a sugar called trehalose. However, both worms and yeast can only enter anhydrobiosis during particular stages of life where they do not eat. So where does the trehalose come from?
Erkut et al. have now addressed this question by studying the metabolism of C. elegans and S. cerevisiae as these species entered anhydrobiosis. The experiments revealed that while preparing for desiccation, both species change their metabolism to favor creating sugars rather than releasing energy. In this process, the worms and yeast use a biochemical pathway called the glyoxylate shunt, which can convert fat or acetic acid into sugar. Genetic mutations that deactivate this pathway severely reduce the ability of both organisms to produce trehalose and tolerate desiccation. From these findings, Erkut et al. conclude that the source of trehalose in non-feeding worms is their fat deposits, while in yeast it is acetate: a molecule that is derived from ethanol, the end-product of the fermentation process.
The glyoxylate shunt had been thought only to be a non-essential biochemical shortcut of another well-known metabolic pathway called the Krebs cycle. Now that Erkut et al. have shown that the glyoxylate shunt has its own specific biological role, further investigation is needed to understand how it is activated to act as a metabolic switch. The molecules that regulate similar metabolic transitions will also need to be identified in future studies. Ultimately, understanding these processes could present new ways of diagnosing and treating metabolic diseases such as diabetes and cancer.
Image credit Pablo Rojas, Wellcome Images
Dried agar plate: Photograph showing an agar plate used to grow bacterial colonies that has been left exposed to the air. Over drying the plate causes cracks and ruptures in the surface of the agar due to dehydration.