In vitro biosynthesis of Ag, Au and Te-containing nanostructures by Exiguobacterium cell-free extracts

Abstract

Background: The bacterial genus Exiguobacterium includes several species that inhabit environments with a wide range of temperature, salinity, and pH. This is why the microorganisms from this genus are known generically as polyextremophiles. Several environmental isolates have been explored and characterized for enzyme production as well as for bioremediation purposes. In this line, toxic metal(loid) reduction by these microorganisms represents an approach to decontaminate soluble metal ions via their transformation into less toxic, insoluble derivatives. Microbial-mediated metal(loid) reduction frequently results in the synthesis of nanoscale structures-nanostructures (NS)-. Thus, microorganisms could be used as an ecofriendly way to get NS. Results: We analyzed the tolerance of Exiguobacterium acetylicum MF03, E. aurantiacum MF06, and E. profundum MF08 to Silver (I), gold (III), and tellurium (IV) compounds. Specifically, we explored the ability of cell-free extracts from these bacteria to reduce these toxicants and synthesize NS in vitro, both in the presence or absence of oxygen. All isolates exhibited higher tolerance to these toxicants in anaerobiosis. While in the absence of oxygen they showed high tellurite-and silver-reducing activity at pH 9.0, whereas AuCl 4 − which was reduced at pH 7.0 in both conditions. Given these results, cell-free extracts were used to synthesize NS containing silver, gold or tellurium, characterizing their size, morphology and chemical composition. Silver and tellurium NS exhibited smaller size under anaerobiosis and their morphology was circular (silver NS), starred (tellurium NS) or amorphous (gold NS). Conclusions: This nanostructure-synthesizing ability makes these isolates interesting candidates to get NS with biotechnological potential.

Biosynthesis of metallic nanoparticles by bacterial cell-free extract

“…The anaerobic or aerobic operation mode can change the morphology of the NPs. 29 For the synthesis of silver NPs, the anaerobic cultivation of microorganisms resulted in smaller NPs (∼40 nm aerobically and ∼20 nm anaerobically). For the CFE-synthesized NPs of the Exiguobacterium acetylicum MF03 strain, the culture form also affected the form.…”

“…CFEs can be used as a crude extract of a target molecule, as uricase to synthesize silver MNPs, 14 selenate reductase to synthesize selenium MNPs, 38 (Pd4)3-GFPuv to synthesize palladium NPs, 43 and nitrate reductase to synthesize silver NPs. 33 To investigate target biomolecules in CFEs and elucidate the biomolecules involved in the biosynthesis of MNPs, some studies also characterize CFE in terms of protein and enzyme content through analyses such as the quantification of total protein content with bovine serum albumin as a standard, 5,33,43 quantification of the number and molecular weight of proteins using the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) technique, 35,36,44 determination of protein concentration by the Bradford protocol 29,42 and determination of enzymatic activity 29 (Table 3).…”

“…It was verified that the metal(oid)-reducing activity was higher in extracts of cells cultured up to the middle of the exponential phase, so it was possible to establish at which moment of bacterial growth the CFE contained the highest concentration of proteins. 29 Tejada-Vaprio et al (2020) speculated that peptides could adjust the morphology of NPs and direct the synthesis even in an environment that contains remnants of the bacterial cells, eliminating the need for purification. Crude lysate (CFE), desalted lysate, and an ion exchange enriched fraction containing (Pd4)3-GFPuv were used to evaluate the hypothesis.…”

“…The cultivation time of bacterial biomass varies from 3 h (ref. 29) to 168 h (7 days). 30 On the other hand, Ashengroph, Khaledi, and Bolbanabad (2020) did not detail the incubation time.…”

In SituBiosynthesis of a Metal Nanoparticle Encapsulated in Alginate Gel for Imageable Drug-Delivery System

“…Considering these points, in vitro biosynthetic strategy emerged as a promising approach. Herein, the metal-binding protein is expressed, then extracted from recombinant hosts, and used to interact with various metal ions, resulting in the corresponding metal NPs . However, using this approach for high-yield production of metal NPs is still challengeable due to the instability of the metal-binding proteins without their existence within a cell wall. , …”