Microbial reduction of hematite: Effects of particle size and exopolysaccharides

COLL 82

Juyoung Ha, jyha@stanford.edu1, Carmen D. Cordova2, Tae Hyun Yoon3, Alfred M. Spormann2, and Gordon E. Brown Jr., gordon@pangea.Stanford.EDU4. (1) Department of Geological & Environmental Sciences, Stanford University, 367 Panama Street, Stanford, CA 94305, (2) Department of Civil and Environmental Engineering, Stanford University, Clark Center for Bio-X, Room E250, 318 Campus Drive, Stanford, CA 94305-5429, (3) Department of Chemistry, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul, 133-791, South Korea, (4) Department of Geological and Environmental Sciences, Stanford Synchrotron Radiation Laboratory, SLAC, 2575 Sand Hill Road, Menlo Park, CA 94025
In this study we have investigated the effect of hematite particle size on the growth rate and extent of dissimilatory iron reduction by Shewanella oneidensis strain MR-1. A mutant strain (Δ4179)of S. oneidensis, which is deficient in exopolysaccharide (EPS) production, was also used. Under anaerobic conditions at pH = 7.4, three types of electron acceptors were utilized, all at 10mM: (1)hematite nanoparticles(avg. diameter = 10nm, surface area(SA)=230 m2/g),(2)hematite macroparticles(avg. diameter=800nm, SA=19 m2/g), and (3)soluble ferric citrate. Increases in cell density caused by the different electron acceptors were observed, with nanoparticles the lowest, macroparticles the intermediate, and soluble ferric citrate the highest cell growth for both ummodified wild type and Δ4179. Regardless of the electron acceptor types, Δ4179 strain showed greater cell productivity than wild type. A comparison of iron reduction by both wild type and Δ4179 strain showed the same trend as the cell growth data. Scanning Transmission X-ray Microscopy (STXM) showed ferrous iron associated with the cell membrane of wild type grown with nanoparticles. SEM and TEM images of samples collected after 36 hour of incubation showed a strong association between the particles and cells for both the wild and Δ4179 strains. The results of this study suggest that differences in hematite particle size influence cell activity and iron reduction rate. We infer when nanoparticles adhere to cells, active sites on cell membrane may have become saturated by particles and hence cell growth and iron reduction were retarded. It is also possible that ferrous iron precipitation on the cell membranes causes an inhibitory effect similar to that of the nanoparticles. The potential role of EPS in the nucleation of ferrous iron precipitates and of suspended hematite particles in the vicinity of the cells, resulting in occlusion of active sites on cell membranes, is also considered.
 

Structure, Interactions and Reactivity at Microbial Surfaces
2:00 PM-5:20 PM, Sunday, 10 September 2006 Sir Francis Drake -- Windsor Room, Oral

Division of Colloid & Surface Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006