“We found that the mineral aggregates, which are produced as a consequence of microbial activity, actually contain a lot of protein,” says Banfield. “This is very interesting because biomineralization has traditionally been thought of as a phenomenon that occurs within a cell, or in contact with it. But in this case, we see an intimate association of proteins and minerals that takes place as far as hundreds of microns away from the cell.”
In other words, in addition to pumping nano-sized sulfide waste particles into the environment, bacteria also pump proteins into the environment. These proteins then sweep the sulfide nanoparticles out of solution into a ball.
Scientists don’t why this occurs. Perhaps it’s a serendipitous accident. Proteins and peptides could be released by bacteria after they die, and are then scavenged by zinc sulfide. Or there could be a physiological reason. Perhaps the bacteria use the protein to sequester their sulfide waste product, which could otherwise accumulate and entomb the bacteria or interfere with their cellular machinery. Think of it as trash pickup at the nanoscale. Regardless, the process stops the spread of metal nanoparticles in natural environments, which is reason enough to explore it further.
“If we understand what causes nanoparticles to aggregate, we have the potential to control their mobility in the subsurface by adding constituents that drive aggregation,” says Banfield.
The scientists also sought to understand the mechanism by which proteins promote nanoparticle aggregation. They found that the presence of cysteine, an amino acid that is a building block to most proteins, yielded the most extensive and prolonged aggregation, with some blobs measuring ten microns in diameter.
Their discovery could also refine t
Source:DOE/Lawrence Berkeley National Laboratory