Ehleringer and Kreuzer-Martin later showed that the oxygen isotope ratios in bacteria similar to anthrax reflected the ratios of the water in which they were cultured, providing clues to where the bacteria were grown.
The method also has been used to track the source of explosives favored by terrorists, and has been proposed as a way to use hair samples from terrorists to determine their past movements, based on isotope ratios in food and water at different locations.
How the New Study Was Performed
Prevailing wisdom says that water inside and outside of cells is identical in terms of ratios of oxygen-18 to oxygen-16, and rare hydrogen-2 to common hydrogen-1.
The paradigm is that water diffuses so quickly into and out of cells that the water inside a cell is indistinguishable from water outside a cell," Hegg says.
The researchers grew E. coli bacteria at body temperature in flasks containing a nutrient-rich liquid culture medium. There were four sets of flasks, each holding a growth medium containing water with a different ratio of oxygen-18 to oxygen-16.
After the bacteria grew for three hours, the contents of each flask were sucked through a filter, leaving a pasty "cake" of bacterial cells with the consistency of wet flour.
Water was extracted from the bacterial cakes by placing each cake in a test tube, freezing the cakes by putting the tubes in liquid nitrogen, using a vacuum to remove the air from each tube, then putting the tubes in boiling water. The water from each cell cake was boiled into steam, which was routed to another tube where the water condensed.
Before undergoing this process, half of the bacterial cakes were washed with water with four different ratios of oxygen-18 to oxygen-16. The washing process allowed researcher
Source:University of Utah Public Relations