(584h) Novel Biogenic Nanomaterials As Nanocatalysts and Anti-Virulence Agents

Microorganisms have the potential to change the oxidation state of metal(loid)s and these microbial processes have opened up a new window for novel applications, for example, biosynthesis of metal(loid) nanomaterials. Microbial processes can synthesize nanomaterials in water under gentle and environmentally benign conditions. Hence, biological processes for the production of nanomaterials have become one of the attractive research focuses in current green nanotechnology towards sustainable development. Many microorganisms can be used to synthesize metal nanomaterials. Among them, Shewanella oneidensis is able to reduce a diverse range of metal(loid)s extracellularly. One research focus in our group is to explore extracellular synthesis of metal(loid)s nanomaterials by S. oneidensis and novel applications of the bacteriogenic nanomaterials. Three examples of our recent research work will be presented.  

(i) Using biosynthesis of silver and silver sulfide nanoparticles as a model, we show that surface proteins MtrC and OmcA significantly affect the size and activity of the extracellular bacteriogenic nanoparticles. Our results suggest that it may be possible to control particle size and activity of the extracellular biogenic nanoparticles via controlled expression of the genes encoding surface proteins. We also reveal that the usually neglected non-cell-associated nanoparticles could have high catalytic activity, underlining the need for novel methods that ensure efficient retention of extracellular nanoparticles in biosynthesis processes.

(ii) Biofilms may serve as a promising system for synthesizing and retaining nanomaterials because of the presence of a sticky matrix composed of extracellular polymeric substances. We show that biofilms can produce and immobilize nanocrystals in the biofilm matrix. The in situ generated nanocrystals in the biofilms exhibit nanocatalytic activities. Our results demonstrate the development of a novel hybrid biofilm-nanocrystal catalytic system, called nanocatalytic biofilms, which may be used to develop novel multifunctional catalysts with both biocatalytic and nanocatalytic activities.

iii) Bacteria typically require iron with concentrations in the µM, i.e., 10^-6 M range to support growth. Human serum concentrations of free iron are maintained as low as 10^-24 M, which pose a serious challenge to pathogenic bacteria that attempt to establish an infection. However, human pathogens can establish infections through self-produced siderophores that can complex Fe(III) to facilitate iron acquisition. We show that an extracellular bacteriogenic nanomaterial significantly inhibits the production of one important siderophore. Using molecular biology tools, we further elucidate the inhibition occurs at the transcriptional level.