Nanoscale Tungsten-Microbial Interface of the Metal Immobilizing Thermoacidophilic Archaeon Metallosphaera sedula Cultivated With Tungsten Polyoxometalate

Abstract

Inorganic systems based upon polyoxometalate (POM) clusters provide an experimental approach to develop artificial life. These artificial symmetric anionic macromolecules with oxidometalate polyhedra as building blocks were shown to be well suited as inorganic frameworks for complex self-assembling and organizing systems with emergent properties. Analogously to mineral cells based on iron sulfides, POMs are considered as inorganic cells in facilitating prelife chemical processes and displaying “life-like” characteristics. However, the relevance of POMs to life-sustaining processes (e.g., microbial respiration) has not yet been addressed, while iron sulfides are very well known as ubiquitous mineral precursors and energy sources for chemolithotrophic metabolism. Metallosphaera sedula is an extreme metallophilic and thermoacidophilic archaeon, which flourishes in hot acid and respires by metal oxidation. In the present study we provide our observations on M. sedula cultivated on tungsten polyoxometalate (W-POM). The decomposition of W-POM macromolecular clusters and the appearance of low molecular weight W species (e.g., WO) in the presence of M. sedula have been detected by electrospray ionization mass spectrometry (ESI-MS) analysis. Here, we document the presence of metalloorganic assemblages at the interface between M. sedula and W-POM resolved down to the nanometer scale using scanning and transmission electron microscopy (SEM and TEM) coupled to electron energy loss spectroscopy (EELS). High-resolution TEM (HR-TEM) and selected-area electron diffraction (SAED) patterns indicated the deposition of redox heterogeneous tungsten species on the S-layer of M. sedula along with the accumulation of intracellular tungsten-bearing nanoparticles, i.e., clusters of tungsten atoms. These results reveal the effectiveness of the analytical spectroscopy coupled to the wet chemistry approach as a tool in the analysis of metal–microbial interactions and microbial cultivation on supramolecular self-assemblages based on inorganic metal clusters. We discuss the possible mechanism of W-POM decomposition by M. sedula in light of unique electrochemical properties of POMs. The findings presented herein highlight unique metallophilicity in hostile environments, extending our knowledge of the relevance of POMs to life-sustaining processes, understanding of the transition of POMs as inorganic prebiotic model to life-sustainable material precursors and revealing biogenic signatures obtained after the decomposition of an artificial inorganic compound, which previously was not associated with any living matter.

Desiccation of the Extreme Thermoacidophile Metallosphaera sedula Grown on Terrestrial and Extraterrestrial Materials

“…Apparently, only certain cell wallmetal interactions can strengthen prokaryotic cell envelopes and augment their structural stability implicating in cell preservation during harsh long-term dehydration. In this regard, the tungsten incorporation by the cell envelope of M. sedula (Blazevic et al, 2019;Milojevic et al, 2019a) may certainly serve as an efficient strengthening strategy, as this is a hard element with the highest melting point and extraordinary properties among all metals. Being suitable for high-temperature applications in energy and lighting technology, and in the space industry, it is also used as alloys, superalloys, and radiation-shielding.…”

“…Being suitable for high-temperature applications in energy and lighting technology, and in the space industry, it is also used as alloys, superalloys, and radiation-shielding. We have previously reported that M. sedula (cultivated on scheelite and W-POM) mineralizes its S-layer via encrusting with crystalline nanoparticles containing tungsten carbide-like structures (Blazevic et al, 2019;Milojevic et al, 2019a). Tungsten exhibits a hardness of ∼9-9.5 on the Mohs hardness scale (Tabor, 1954) and can potentially provide an efficient barrier against water loss, warranting preservation of cell integrity after desiccation.…”

“…Chemolithoautotrophic cultivation of M. sedula was performed in DSMZ88 Sulfolobus medium defined above as described earlier (Milojevic et al, 2019a,b). Chemolithoautotrophic cultures were supplemented with 10 g/L of (i) a tungsten-bearing scheelite ore containing impurities of Mn and Fe oxides (Blazevic et al, 2019; (Contant et al, 2007;Milojevic et al, 2019a); (iii) the stony meteorite NWA 1172 (H5 ordinary chondrite Northwest Africa 1172) (Russell et al, 2002;Milojevic et al, 2019b; see Supplementary Tables 1, 2 for chemical and mineralogical composition); (iv) multimetallic waste products (voestalpine BÖHLER Edelstahl GmbH & Co KG); and (v) multimetallic Martian regolith simulants (MRSs; Kölbl et al, 2017; see Supplementary Tables 1, 2 for chemical and mineralogical composition). The metalcontaining compounds were temperature sterilized in a heating chamber (180 • C) for a minimum of 24 h prior to autoclaving (121 • C for 20 min).…”

“…Dehydration by evaporation (up to 2 months) has been applied toward microbial cultures harvested after cultivation of M. sedula with W-POM (Milojevic et al, 2019a). The crystalline material obtained after dehydration was examined by SEM.…”

“…Our recent studies indicate that this metallophilic archaeon can form a metal-bearing crust encasing its S-layer (Blazevic et al, 2019;Milojevic et al, 2019a,b). Examining the physiology of this extreme metallophilic archaeon cultivated with diverse metal-bearing substrates of terrestrial (Blazevic et al, 2019;Milojevic et al, 2019a) and extraterrestrial origin (Kölbl et al, 2017;Milojevic et al, 2019b), we have observed its selective preservation under the conditions of desiccation. Here, we report on several cases of the metal-grown polyextremophilic archaeon M. sedula, which were particularly beneficial to preserve its viability and cellular integrity after long-term desiccation.…”