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that a 150-kilodalton outer-membrane protein plays a prominent role in transferring electrons from the bacterium to the mineral, Lower says. "This protein is not always on the surface," Lower explains. Under HEN OXYGEN CANfr SERVE The researchers measured in aerobic conditions, when as the final electron real time the forces between one there's no need to respire acceptor in respiration, live bacterium and the goethite minerals, it's not there. some bacteria breathe dust surface as a function of distance But under anaerobic instead. Under anaerobic condi under aerobic and anaerobic con conditions and only in tions, the metal-reducing bac ditions. They compared the data the presence ofgoethite, terium Shewanella oneidensis, for with measurements against diait is there—as if the bac example, uses iron-containing spore, a mineral with the same terium senses the ab minerals like goethite as its ter surface properties as goethite, but sence of oxygen, as well CONTACT A single minal electron acceptor. Because one that does not accept elec these minerals are solids under trons from S. oneidensis. They also as the presence of a ben Shewanella oneidensis eficial mineral, and bacterium at the tip of a normal environmental condi experimented with goethite and changes the biomole- cantilever registers its tions, the electron transfer must a dead bacterium. cules on its surface on the attraction or repulsion to the occur directly from the bac They find that the attraction terium to the mineral. between S. oneidensis and goethite basis ofwhat it is sensing. surface of goethite through The data represent the reflections of a laser beam off is strongest when oxygen is Bacteria that respire minerals first "quantitative evi the top of the cantilever. absent, when direct electron are important in diverse processes, dence that bacteria rectransfer should occur. Further including the weathering of rocks ognize inanimate objects, like a more, theoretical modeling of the and the biogeochemical cycling of mineral surface," he explains.— data with iron reductases associ nutrients. But the mechanism of MAUREEN ROUHI ated with this bacterium suggests this respiration mode has been a mystery that researchers only now are beginning to unveil. Using a NANOSCIENCE new technique called biological force microscopy they have quan titatively measured the interac tive forces between an 5. oneidensis ene-chip technology cell and the surface of goethite. ι may have just gotten a The bacterium expresses a specific boost, thanks to protein to mediate the interaction, developments in DNA the data suggest. detection schemes at Northwestern University. In biological force microscopy, Chemistry professor Chad live cells are attached to a small A. Mirkin, postdoctoral bead at the end of an atomic force associate T. Andrew Taton, microscope tip. The technique and graduate student Gang allows force measurements at Lu have devised a technique sub-nanonewton resolution. It in which 50- and 100-nmwas developed by Steven K. sized gold particles serve as Lower, a recent Ph.D. in geolog colored probes to selectively detect two different DNA target sequences in a single solution ical sciences and biochemistry [J. Am. Chem. Soc, 123, 5164 (2001)]. Demonstrating the procedure, the group cohybridizes from Virginia Polytechnic Insti oligonucleotide-modified particles and oligonucleotide targets to arrays of DNA attached to glass tute & State University; Michael slides. Light Ihv) scattered from the particles is imaged as bright spots on a dark background; the F. Hochella Jr., a Virginia Tech 50-nm particles scatter green light, and 100-nm particles appear orange. The chemists assessed professor of geochemistry and the method's selectivity in temperature-dependency tests using targets with a single base-pair mineralogy; and Terry J. Bevmismatch. Slightly mismatched targets (green) dissociate over a narrow range (55 to 60 °C) as eridge, a professor of microbiol indicated by a color change that is readily visible in real time. The technique should be extendable ogy at the University of Guelph [Science, 2 9 2 , 1 3 6 0 (2001)}. In to additional colors using nanoparticles of various sizes and compositions, the researchers note. They add that the method's selectivity may be suitable for studying single-nucleotide polymor July, Lower will be an assistant phism and genetic disease mutations.—MITCH JACOBY professor of geology at the Uni versity ofMaryland, College Park.
LIVING ON DUST
Bacteria recognize mineral surface, new force microscopy technique shows
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Colorful Method For Detecting DNA
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