Elucidation of biological nanoparticle formation mechanisms

Several bacteria can reduce heavy metals and form discrete, homogeneous metallic deposits on the cell surface. Examples include Desulfovibrio desulfuricans and Escherichia coli, which both mediate the reduction of precious metals in the presence of H₂ (1). These bio-nanoparticles (NPs) have unique catalytic properties and would be highly useful in industrial settings, e.g. as cracking catalysts for breaking down large organic polymers, and bio-NPs are attractive as eco-friendly, sustainable alternatives to physico-chemically synthesised NPs. 

Although the catalytic properties of bio-NPs have been studied in detail, so far the molecular mechanisms involved in their formation are poorly characterised. The aim of this project is to elucidate the molecular mechanism(s) of bio-NP deposition. The project will begin in 2014 by the development of screening assays to search for mutants defective in bio-NP formation. Once the assays are up and running, we will screen libraries of E. coli knock-out mutants to identify candidate genes. In parallel, we will use bioinformatics tools to identify candidate genes that will be knocked out in a more targeted approach. Once candidate genes affecting bio-NP deposition have been identified, the defects will be verified using electron microscopy and other techniques. This will allow elucidation of the molecular pathways leading to bio-NP formation and the proteins involved in the critical steps.
 
The results of this work will provide an understanding of the biological pathways involved in bio-NP formation. Understanding all the components will allow manipulation of bio-NP pathways to produce higher yields, catalysts optimised for different applications, or NPs with specific electronic or magnetic properties. Knowledge gained from E. coli could be transferred to other industrially relevant bacteria (e.g. Bacillus sp.). Our basic research into bio-NP formation will have relevance for industry (production of catalysts, nanoparticles for electronic applications, biorecovery of precious metals) and bioremediation efforts (detoxification of heavy metal ions and other compounds in the environment). 

Fig 1: Two electron microscopy images of bacteria producing bio-NPs. 

Publications:

Chauhan N, Wrobel A, Skurnik M, Leo JC. Yersinia adhesins: an arsenal for infection. Proteomics Clin Appl. Invited review, to be submitted by 30.1.2016.

Deplanche K. and Macaskie L. Biorecovery of gold by Escherichia coli and Desulfovibrio desulfuricans. Biotechnology and Bioengineering 99, 1055-64 (2008).

Mühlenkamp M, Oberhettinger P, Leo JC, Linke D, Schütz M: Yersinia adhesin A (YadA) – beauty and beast. Int J Med Microbiol., 305(2): 252-8 Review.

Leo JC, Oberhettinger P, Schütz M, Linke D: The inverse autotransporter family: Intimin, Invasin and related proteins. Int J Med Microbiol., epub ahead of print. DOI:10.1016/j.ijmm.2014.12.011. Review.

Shen X, Bonde JS, Kamra T, Bülow L, Leo JC, Linke D, Ye L (2014): Bacterial imprinting at Pickering emulsion interfaces. Angew Chem Int Ed Engl., 53(40):10687-90.