Proteins sequester Zinc nanoparticles

Biofilms produced by sulfate-reducing bacteria may help clean up contaminated environments by extracting harmful metals from anoxic waters and sequestering them into metal-sulfide nanoparticles. But would these particles disperse or redissolve if conditions were to change? Apparently not, according to research reported by John W. Moreau of the University of California, Berkeley, and colleagues, who found that the microbes within the biofilms produce proteins that keep the particles stuck in dense spherical aggregates (Science 2007, 316, 1600). The researchers collected biofilms from a flooded lead and zinc mine in Wisconsin. They used transmission electron microscopy, secondary ion microprobe mass spectrometry, and synchrotron radiation Fourier transform infrared spectroscopy to confirm that the nitrogen content in the biofilms was organic, supporting polypeptide or protein origins. Low protein concentration and the complex biofilm structure prevented further characterization of the proteins, so the researchers tested synthetic ZnS nanoparticles in the presence of individual amino acids. The results suggest that cysteine, in particular, triggers aggregation of the nanoparticles.