Guanine crystal formation by bacteria

Abstract

Background Guanine crystals are organic biogenic crystals found in many organisms. Due to their exceptionally high refractive index, they contribute to structural color and are responsible for the reflective effect in the skin and visual organs in animals such as fish, reptiles, and spiders. Occurrence of these crystals in animals has been known for many years, and they have also been observed in eukaryotic microorganisms, but not in prokaryotes. Results In this work, we report the discovery of extracellular crystals formed by bacteria and reveal that they are composed of guanine monohydrate. This composition differs from that of biogenic guanine crystals found in other organisms, mostly composed of β anhydrous guanine. We demonstrate the formation of these crystals by Aeromonas and other bacteria and investigate the metabolic traits related to their synthesis. In all cases studied, the presence of the bacterial guanine crystals correlates with the absence of guanine deaminase, which could lead to guanine accumulation providing the substrate for crystal formation. Conclusions Our finding of the hitherto unknown guanine crystal occurrence in prokaryotes extends the range of organisms that produce these crystals to a new domain of life. Bacteria constitute a novel and more accessible model to study the process of guanine crystal formation and assembly. This discovery opens countless chemical and biological questions, including those about the functional and adaptive significance of their production in these microorganisms. It also paves the road for the development of simple and convenient processes to obtain biogenic guanine crystals for diverse applications.

Elastic Guanine-Based Single Crystals with Optical Waveguiding Properties: Toward Tailored Bioinspired Materials

“…Our findings are in line with similar recent results for seven biogenic guanine crystalline samples, where intracrystalline dopants, such as hypoxanthine and xanthine, were observed . More generally, in biogenic systems, it was shown that the guanine crystals are not pure, but occlude homogeneous mixtures of other purines, even in large amounts (up to 20% of hypoxanthine), without significantly altering the crystal structure of the guanine host. , However, unlike synthetic doped guanine crystals studied by other authors, the dopants were not thought to exert a significant influence over crystal shape or optical properties.…”

“…24 Very recently, prokaryotes were found for the first time to produce guanine monohydrate crystals. 25 To date, there are a total of three different guanine crystal forms reported, the α 26 and β 18 anhydrous polymorphs and one monohydrate. 27 Interestingly, even though both anhydrous phases exhibit similar crystal morphology, in all cases where the crystalline form of the biogenic guanine was determined (spiders, fish, and copepods), the β polymorph was identified, 18 while the α form was obtained only in vitro.…”

“…Occurrence of these crystals in animals has been known for many years, and they have also been observed in eukaryotic microorganisms . Very recently, prokaryotes were found for the first time to produce guanine monohydrate crystals . To date, there are a total of three different guanine crystal forms reported, the α and β anhydrous polymorphs and one monohydrate .…”

Structure Determination of Biogenic Crystals Directly from 3D Electron Diffraction Data

“…Until now, the inability to directly determine the structures of biogenic crystals has limited the rate of progress in organic biomineralization. We anticipate that 3D ED will play a major role in the future exploration of recently discovered uncharacterized molecular biocrystals. ,, …”

“…16,52,53 CCDC 2304787 contains the supplementary crystallographic data for the spider guanine structure reported in this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.…”