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.

Department of Experimental Plant Biology Faculty of Science Charles University Prague 2 Czech Republic

Department of Molecular Biology and Genetics Faculty of Science University of South Bohemia České Budějovice Czech Republic

Department of Zoology Faculty of Science Charles University Prague 2 Czech Republic

Institute of Parasitology Czech Academy of Sciences České Budějovice Czech Republic

Institute of Physics Faculty of Mathematics and Physics Charles University Prague 2 Czech Republic

See more in PubMed

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.

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

Raven JA, Knoll AH. Non-skeletal biomineralization by eukaryotes: matters of moment and gravity. Geomicrobiol J. 2010;27:572–84. doi: 10.1080/01490451003702990. DOI

Creutz CE, Mohanty S, Defalco T, Kretsinger RH. Purine composition of crystalline cytoplasmic inclusions of Paramecium tetraurelia. Protist. 2002;153:39–45. doi: 10.1078/1434-4610-00081. PubMed DOI

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. doi: 10.1016/j.jsb.2019.04.009. PubMed DOI

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. doi: 10.1016/j.algal.2017.02.009. DOI

Roush AH. Crystallization of purines in the vacuole of Candida utilis. Nature. 1961;190:449. doi: 10.1038/190449a0. PubMed DOI

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. doi: 10.1073/pnas.2005460117. PubMed DOI PMC

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

Tadepalli S, Slocik JM, Gupta MK, Naik RR, Singamaneni S. Bio-optics and bio-inspired optical materials. Chem Rev. 2017;117:12705–63. doi: 10.1021/acs.chemrev.7b00153. PubMed DOI

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. doi: 10.1126/science.aam9506. PubMed DOI

Wagner A, Wen Q, Pinsk N, Palmer BA. Functional molecular crystals in biology. Isr J Chem. 2021;61:668–78. doi: 10.1002/ijch.202100069. DOI

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. doi: 10.1016/S0932-4739(97)80007-7. DOI

Yamashita H, Kobiyama A, Koike K. Do uric acid deposits in zooxanthellae function as eye-spots? PLoS ONE. 2009;4:1–9. doi: 10.1371/journal.pone.0006303. PubMed DOI PMC

Kourkoulou A, Pittis AA, Diallinas G. Evolution of substrate specificity in the nucleobase-ascorbate transporter (NAT) protein family. Micro Cell. 2018;5:280–92. doi: 10.15698/mic2018.06.636. PubMed DOI PMC

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. doi: 10.1073/pnas.0800141105. PubMed DOI PMC

Boswell-Casteel RC, Hays FA. Equilibrative nucleoside transporters—a review. Nucleosides Nucleotides Nucleic Acids. 2017;36:7–30. doi: 10.1080/15257770.2016.1210805. PubMed DOI PMC

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. doi: 10.2147/VHRM.S115080. PubMed DOI PMC

Self-Assembly of Accumulated Sphingolipids into Cytotoxic Fibrils in Globoid Cell Leukodystrophy and Their Inhibition by Small Molecules In Vitro

Eating the brain - A multidisciplinary study provides new insights into the mechanisms underlying the cytopathogenicity of Naegleria fowleri

Massive Accumulation of Strontium and Barium in Diplonemid Protists