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A new method to measure iron reduction at a distance based on depositing microbial iron [Fe(III)] (hydr)oxide within nanoporous glass beads is developed. It shows that CymA and menaquinone are required for both direct and indirect mineral reduction, whereas MtrB and OmcB contribute to but are not absolutely required for iron reduction at a distance.

The effects of an environmental strain of Pseudomonas aeruginosa on Ti[O.sub.2] nanoparticle agglomerates formed in aqueous media are studied. The results have provided a novel role for bacteria in the environmental transport of engineered nanoparticles, such as growth-independent, bacterially mediated size and mass alterations of Ti[O.sub.2] nanoparticle agglomerates.

Nanoscale titanium dioxide (TiO2) is increasingly used in consumer goods and is entering waste streams, thereby exposing and potentially affecting environmental microbes. Protozoans could either take up TiO2 directly from water and sediments or acquire TiO2 during bactivory (ingestion of bacteria) of TiO2-encrusted bacteria. Here, the route of exposure of the ciliated protozoan Tetrahymena thermophila to TiO2 was varied and the growth of, and uptake and accumulation of TiO2 by, T. thermophila were measured. While TiO2 did not affect T. thermophila swimming or cellular morphology, direct TiO2 exposure in rich growth medium resulted in a lower population yield. When TiO2 exposure was by bactivory of Pseudomonas aeruginosa, the T. thermophila population yield and growth rate were lower than those that occurred during the bactivory of non-TiO2-encrusted bacteria. Regardless of the feeding mode, T. thermophila cells internalized TiO2 into their food vacuoles. Biomagnification of TiO2 was not observed; this was attributed to the observation that TiO2 appeared to be unable to cross the food vacuole membrane and enter the cytoplasm. Nevertheless, our findings imply that TiO2 could be transferred into higher trophic levels within food webs and that the food web could be affected by the decreased growth rate and yield of organisms near the base of the web. [ABSTRACT FROM AUTHOR]