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Proteins limit nanoparticle dispersal: sulfate-reducing bacteria

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ZnS aggregates (spheres) associated with organic polymers / Moreau et al.. / LicenseCopyright - All Rights Reserved

Extracellular proteins of some sulfate-reducing bacteria limit the dispersal of nanoparticles by aggregating them.

BIOMIMICRY TAXONOMY
Summary
In the waters of a lead-zinc mine in Wisconsin, scientists may have found a solution to how we can clean heavy metals out of subsurface waters. Their findings may also provide clues to how we can mimic nature to clean up other nanoparticles. It was already known that aggregates of sulfate-reducing bacteria (1 and 2 in diagram below) release sulfide, which binds with zinc to sequester it into nanoparticles (3). However, that doesn’t permanently remove them from water because they remain mobile and soluble. The researchers found that proteins and polypeptides released by sulfate-reducing bacteria create spheres of zinc sulfide nanocrystals (4). These spheres are larger aggregates, and have limited ability to disperse and pollute ground and surface water. The key to the clumping was the inclusion of the proteins into pores on the spheres. Cysteine or cysteine-rich polypeptides or proteins cause larger particle size (5).

It is unclear whether the proteins, amino acids, and polypeptides are released into the environment when the bacteria die and are scavenged by hydrophobic zinc sulfide surfaces, or whether the bacteria export them while alive.

Scorpion Impact Illustration
How sulfate-reducing bacteria aggregate nanoparticles. Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.

Excerpt
Analysis revealed an "intimate association of proteins with spheroidal aggregates of biogenic zinc sulfide nanocrystals, an example of extracellular biomineralization. Experiments involving synthetic zinc sulfide nanoparticles and representative amino acids indicated a driving role for cysteine in rapid nanoparticle aggregation. These findings suggest that microbially derived extracellular proteins can limit the dispersal of nanoparticulate metal-bearing phases, such as the mineral products of bioremediation, that may otherwise be transported away from their source by subsurface fluid flow." (Moreau et al. 2007:1600, 1602)
About the inspiring organism
Med_zns_eharrington Bacteria
Bacteria

Learn more at EOL.org
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist


Bioinspired products and application ideas

Application Ideas: The mechanism/chemical could be mimicked to prevent dispersion of nanoparticles; remediation of nanoparticles and toxic metals.

Industrial Sector(s) interested in this strategy: Bioremediation

Experts
Banfield Group
Jillian Banfield
Earth and Planetary Science, University of California, Berkeley
References
Moreau JW, Weber PK, Martin MC, Gilbert B, Hutcheon ID, Banfield JF. 2007. Extracellular Proteins Limit the Dispersal of Biogenic Nanoparticles. Science. 316(5831): 1600-1603.
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Moreau JW, Webb RI, Banfield JF. 2004. Ultrastructure, aggregation-state, and crystal growth of biogenic nanocrystalline sphalerite and wurtzite. American Mineralogist. 89(7): 950-960.
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Labrenz M; Druschel GK; Thomsen-Ebert T; Gilbert B; Welch SA; Kemner KM; Logan GA; Summons RE; De Stasio G; Bond PL; Lai B; Kelly SD; Banfield JF. 2000. Formation of sphalerite (ZnS) deposits in natural biofilms of sulfate-reducing bacteria. Science. 290: 1744-1747.
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