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Revisiting biocrystallization: purine crystalline inclusions are widespread in eukaryotes


Despite the widespread occurrence of intracellular crystalline inclusions in unicellular eukaryotes, scant attention has been paid to their composition, functions, and evolutionary origins. Using Raman microscopy, we examined >200 species from all major eukaryotic supergroups. We detected cellular crystalline inclusions in 77% species out of which 80% is composed of purines, such as anhydrous guanine (62%), guanine monohydrate (2%), uric acid (12%) and xanthine (4%). Our findings shifts the paradigm assuming predominance of calcite and oxalates. Purine crystals emerge in microorganisms in all habitats, e.g., in freshwater algae, endosymbionts of reef-building corals, deadly parasites, anaerobes in termite guts, or slime molds. Hence, purine biocrystallization is a general and ancestral eukaryotic process likely present in the last eukaryotic common ancestor (LECA) and here we propose two proteins omnipresent in eukaryotes that are likely in charge of their metabolism: hypoxanthine-guanine phosphoribosyl transferase and equilibrative nucleoside transporter. Purine crystalline inclusions are multifunctional structures representing high-capacity and rapid-turnover reserves of nitrogen and optically active elements, e.g., used in light sensing. Thus, we anticipate our work to be a starting point for further studies spanning from cell biology to global ecology, with potential applications in biotechnologies, bio-optics, or in human medicine.

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Fig. 1: Distribution of purine inclusions identified by Raman microscopy in the eukaryotic tree of life.
Fig. 2: Proposed scheme of guanine inclusions metabolism with emphasis on the transporters potentially involved.

Data availability

All data generated or analysed during this study are included in this published article and its Supplementary Information files.


  1. Darwin C. Journal of Researches Into the Geology and Natural History of the Varoius Countries Visited by HMS Beagle, Under the Command of Captain Fitzroy from 1832 to 1836 by Charles Darwin. Colburn, London; 1840.

  2. Haeckel E. Kristallseelen: Studien über das anorganische Leben. Leipzig: Alfred Kröner Verlag; 1917.

  3. Raven JA, Knoll AH. Non-skeletal biomineralization by eukaryotes: matters of moment and gravity. Geomicrobiol J. 2010;27:572–84.

    CAS  Article  Google Scholar 

  4. Creutz CE, Mohanty S, Defalco T, Kretsinger RH. Purine composition of crystalline cytoplasmic inclusions of Paramecium tetraurelia. Protist. 2002;153:39–45.

    CAS  Article  Google Scholar 

  5. Jantschke A, Pinkas I, Hirsch A, Elad N, Schertel A, Addadi L, et al. Anhydrous β-guanine crystals in a marine dinoflagellate: Structure and suggested function. J Struct Biol. 2019;207:12–20.

    CAS  Article  Google Scholar 

  6. Moudříková Š, Nedbal L, Solovchenko A, Mojzeš P. Raman microscopy shows that nitrogen-rich cellular inclusions in microalgae are microcrystalline guanine. Algal Res. 2017;23:216–22.

    Article  Google Scholar 

  7. Roush AH. Crystallization of purines in the vacuole of Candida utilis. Nature. 1961;190:449.

    CAS  Article  Google Scholar 

  8. Mojzeš P, Gao L, Ismagulova T, Pilátová J, Moudříková Š, Gorelová O, et al. Guanine, a high-capacity and rapid-turnover nitrogen reserve in microalgal cells. Proc Natl Acad Sci. 2020;117:32722–30.

    Article  Google Scholar 

  9. Sterner RW, Elser JJ. Ecological stoichiometry: the biology of elements from molecules to the biosphere. Encyclopedia of Ecology, Five-Volume Set. Princeton, New Jersey, USA: Princeton University Press; 2002.

    Google Scholar 

  10. Tadepalli S, Slocik JM, Gupta MK, Naik RR, Singamaneni S. Bio-optics and bio-inspired optical materials. Chem Rev. 2017;117:12705–63.

    CAS  Article  Google Scholar 

  11. Palmer BA, Taylor GJ, Brumfeld V, Gur D, Shemesh M, Elad N, et al. The image-forming mirror in the eye of the scallop. Science. 2017;358:1172–5.

    CAS  Article  Google Scholar 

  12. Wagner A, Wen Q, Pinsk N, Palmer BA. Functional molecular crystals in biology. Isr J Chem. 2021;61:668–78.

    CAS  Article  Google Scholar 

  13. Kuhlmann HW, Bräucker R, Schepers AG. Phototaxis in Porpostoma notatum, a marine scuticociliate with a composed crystalline organelle. Eur J Protistol. 1997;33:295–304.

    Article  Google Scholar 

  14. Yamashita H, Kobiyama A, Koike K. Do uric acid deposits in zooxanthellae function as eye-spots? PLoS ONE. 2009;4:1–9.

    Article  Google Scholar 

  15. Kourkoulou A, Pittis AA, Diallinas G. Evolution of substrate specificity in the nucleobase-ascorbate transporter (NAT) protein family. Micro Cell. 2018;5:280–92.

    CAS  Article  Google Scholar 

  16. Sawada K, Echigo N, Juge N, Miyaji T, Otsuka M, Omote H, et al. Identification of a vesicular nucleotide transporter. Proc Natl Acad Sci USA. 2008;105:5683–6.

    CAS  Article  Google Scholar 

  17. Boswell-Casteel RC, Hays FA. Equilibrative nucleoside transporters—a review. Nucleosides Nucleotides Nucleic Acids. 2017;36:7–30.

    CAS  Article  Google Scholar 

  18. Bove M, Cicero AFG, Veronesi M, Borghi C. An evidence-based review on urate-lowering treatments: implications for optimal treatment of chronic hyperuricemia. Vasc Health Risk Manag. 2017;13:23–8.

    CAS  Article  Google Scholar 

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We express our gratitude to Lukáš Falteisek, Richard Dorrell, Jan Petrášek, Stanislav Volsobě, Kateřina Schwarzerová and Jana Krtková for constructive discussions. English has been kindly corrected by William Bourland. Furthermore, we thank to Dovilė Barcytė, William Bourland, Antonio Calado, Dora Čertnerová, Yana Eglit, Ivan Fiala, Martina Hálová, Miroslav Hyliš, Dagmar Jirsová, Petr Kaštánek, Viktorie Kolátková, Alena Kubátová, Alexander Kudryavtsev, Frederik Leliaert, Julius Lukeš, Jan Mach, Joost Mansour, Jan Mourek, Yvonne Němcová, Fabrice Not, Vladimír Scholtz, Alastair Simpson, Pavel Škaloud, Jan Šťastný, Róbert Šuťák, Daria Tashyreva, Dana Savická, Jan Šobotník, Zdeněk Verner, Jan Votýpka for kindly providing cultures and taxonomic identifications.


Financial support from the Czech Science Foundation (grants 17–06264 S, 19–19297 S, 20-16549Y, 21-03224S, and 21-26115 S); Grant Agency of Charles University (grant 796217), Charles University Research Center program No. 204069, European Regional Development Fund and the state budget of the Czech Republic, projects no. CZ.1.05/4.1.00/16.0340, CZ.1.05/4.1.00/16.0347, CZ.2.16/3.1.00/21515 and CZ.02.1.01/16_019/0000759, LM2018129.

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JP conceived the study, handled the cell cultures, performed the Raman measurements and data processing, prepared the graphics and videos and wrote the paper; TP and MO performed phylogenetic analyses and profiling; PM conceived the study and corrected the paper; IČ provided the cell cultures and corrected the paper. All authors discussed and approved the paper.

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Correspondence to Jana Pilátová.

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Pilátová, J., Pánek, T., Oborník, M. et al. Revisiting biocrystallization: purine crystalline inclusions are widespread in eukaryotes. ISME J (2022).

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