Potential Environmental Interactions of Bacteria and Manufactured Nanomaterials.

Upon release into the environment, manufactured nanomaterials (MNMs) will encounter bacteria wherein many fates and effects are conceivable including binding, uptake, breakdown and toxicity.  In this presentation, a synthesis of interaction potentials is described, stemming from our work with several MNMs and bacterial taxa.  Initially agglomerated titania MNMs can disagglomerate upon bacterial cell surface contact and preferential sorption.  Yet adhesion of MNMs to cell surfaces is observed to vary with MNM and with bacterial strain, including across several gram positive and gram negative bacteria.  Heavy metal-containing MNMs that dissolve extracellularly inhibit growth in the dark due partly to dissolved ions diffusing into, and accumulating within, cells.  However, CdSe quantum dots (QDs) appear to enter cells intact through permeabilized membranes occurring with high extracellular reaction oxygen species (ROS) conditions.  Once inside cells, CdSe QDs are activated, then bioaccumulate as QDs and constituent metals.  Metal oxide MNMs, e.g. CeO₂, ZnO and TiO₂, also inhibit growth in the dark but at much higher concentrations than CdSe QDs; dose-response relationships are also highly taxa-dependent.  Metal oxide MNM uptake into cells is not observed.  Taken together, our results support the following bacterial interactions with metal/metalloid and metal oxide MNMs: 1) extracellular binding, but not as a prerequisite for 2) cell membrane damage, which is a prerequisite for 3) cellular entry of intact MNMs, and 4) growth impairment independent of MNM uptake.  These interactions represent potential outcomes under environmental conditions where bacterial growth effects can have profound ecosystem consequences.