Crystalline nutrient reservoir and "safety molecule"

Jülich, February 9, 2021 - Vast areas of the oceans are nutrient-poor, and nitrogen is particularly lacking. Nitrogen is an essential nutrient that also influences the productivity and growth of microalgae. Yet many free-living microalgae - the phytoplankton - as well as those that live in symbiosis with corals, thrive in very nutrient-poor environments. An international team of researchers with Jülich participation found that microalgae can very quickly store nitrogen from a variety of sources in the form of guanine crystals to release it when needed - an important survival strategy, also for corals. Crystalline guanine is shown here to be an evolutionarily ancient, multifunctional tool of nature. The results of the study have now been published in the renowned journal Proceedings of National Academy of Sciences of the United States of America (PNAS).

Guanine is a nitrogen base - one of the four nucleic bases that make up the genetic code of all living things on earth. As a molecule, guanine provides free chemical energy to all life forms. In many organisms, crystalline guanine also serves as an optical modulator and light reflector for signaling or camouflage. It is the reason fish scales appear silvery.

Symbiodiniaceae alga distracted from Acropora Millepora, a widespread coral on the Great Barrier Reef. Crystalline Guanine was imaged in the laser reflection mode (blue), while chloroplasts via fluorescence of chlorophyll (red).
Anya Salih, University of Western Sydney

The research team from Jülich, Prague, Moscow und Sydney studied the chemical nature of crystalline inclusions in various microalgae and found that they are largely composed of guanine. Using isotopically labeled nutrients, they were able to show that microalgae were able to synthesize crystalline guanine from various nitrogen sources such as nitrate, ammonium or urea, or to take up guanine supplied to their environment in large quantities. If the external nitrogen supply stopped, the crystalline nutrient store was used for algal growth.

"Microalgae need phosphorus and nitrogen to grow. But an excess of nutrients can be harmful, especially if the ratio of nitrogen to phosphorus is altered", explains Dr. Ladislav Nedbal from the Jülich Institute of Plant Sciences, who coordinated the research project. One reason for this is man-made "pollution" with nutrients that enter the sea from fertilizers, for example. "But guanine is insoluble at physiological pH and less metabolically active than several other nitrogen-containing compounds, which allows its accumulation in large amounts and storage within cells without the risk of metabolic disorders."

This discovery also provides a clue to how sensitive organisms such as reef corals survive fluctuating nutrient conditions or high nutrient stress - guanine is proving to be a kind of "safety molecule" here. For example, Australian studies using corals grown in aquaria and sampled from the Great Barrier Reef showed that microalgae living in symbiosis with corals are able to take up and store crystalline guanine from the corals. High levels of nutrients caused by pollution reduce the corals' tolerance to heat and light, and they repel their microalgae. A further study will investigate what role guanine plays in this.

Original publication:
Peter Mojzeš, Lu Gao, Tatiana Ismagulova, Jana Pilátová, Sárka Moudriková, Olga Gorelova, Alexei Solovchenko, Ladislav Nedbal, and Anya Salih: Guanine, a high-capacity and rapid-turnover nitrogen reserve in microalgal cells. PNAS December 22, 2020 117 (51) 32722-32730;

Institute of Bio- and Geosciences, Plant Sciences (IBG-2)

Dr. Ladislav Nedbal
Institute of Bio- and Geosciences, Plant Sciences (IBG-2)
Tel.: 02461 61-96720

Last Modified: 22.05.2022