You may have heard about certain potential dangers of nanotechnology; I like to write about some of them on occasion; and you probably know about the almost lost battle against so called superbugs, those pesky bacteria that evolved in hospitals to become resistant against all our drugs. Now combine these for something a little more scary: Fast-track evolution towards superbugs.
Nanoparticles accelerate horizontal gene transfer between bacteria, helping them to become resistant against multiple antibiotics. Especially the alumina nanoparticles used to bind heavy metals in waste water treatment plants have now been shown to invade the cells readily through the cell membrane. Such invasions seem to quite generally trigger bacteria to approach other microorganisms in order to swap genes, which is a way to accelerate adaptation in a rapidly changing environment.
As Zhigang Qiu et. al. now describe in the Proceedings of the National Academy of Sciences , the transfer of genes can increase by up to 200 times, helping diseases to acquire resistance against antibiotics from our harmless gut bacteria in waste water. The particles even help the exchange between types of organisms that usually seldom swap genes, like between Escherichia Coli and Salmonella.
“Antibiotic resistance is a worldwide public health concern. Conjugative transfer between closely related strains or species of bacteria is an important method for the horizontal transfer of multidrug-resistance genes. The extent to which nanomaterials are able to cause an increase in antibiotic resistance by the regulation of the conjugative transfer of antibiotic-resistance genes in bacteria, especially across genera, is still unknown. Here we show that nanomaterials in water can significantly promote the horizontal conjugative transfer of multidrug-resistance genes” Source: abstract 
The concentration of nanoparticles used in the experiments was lower than that employed in novel waste water treatment test projects. Such is worrisome, but one could of course also give this a positive spin: At least bacteria are ready for the threat that nanotechnology poses. Triggered by cell stress, certain genes are activated and the microorganisms start evolving faster. It won’t help us much, but hey, let’s not be anthropocentric bio-racists. ;-)
 Qiu et al: “Nanoalumina promotes the horizontal transfer of multiresistance genes mediated by plasmids across genera” PNAS pdf