Monitoring Nanoscale Changes Within and Around Single Microbes From Environmental Samples


Research results from the Natural and Accelerated Bioremediation Research program (NABIR) researchers, Dr. Kenneth M. Kemner of Argonne National Laboratory (ANL), Dr. Kenneth H. Nealson of the University of Southern California, and colleagues appear in the October 22, 2004, issue of Science. Using a microprobe technology at the Advanced Photon Source (APS), Dr. Kemner and colleagues document changes in morphology and elemental composition of both planktonic (i.e. free-swimming) and surface adhered, single bacteria before and after exposure to high concentrations of toxic Cr(VI). Dr. Kemner uses highly focused synchrotron-based x-rays to probe biogeochemical processes occurring at the microbe-mineral interface. The analytical technique developed by Kemner is noninvasive and allows the researchers to interrogate living, hydrated biological samples at the nanometer scale (150nm). The results show that surface adhered bacteria tolerate chromium better than planktonic cells and accumulate elements such as calcium and phosphorus associated with the production of extracellular polysaccharide (EPS). X-ray absorption near-edge spectroscopy (XANES) analyses of surface adhered bacteria implied that Cr(VI) was reduced to Cr(III) within the EPS layer. Several differences also were observed in the distribution of transition metal abundance within surface adhered cells relative to planktonic cells. These results demonstrate that it is now possible to monitor nanoscale changes in elemental composition and redox chemistry within and around a single bacterial cell, an ability that could prove invaluable during investigations of biogeochemical processes in the environment.