HR: 0830h
AN: B41D-0924    [PDF]
TI: Changes in Microbial Community Structure With Depth in a Simulated Vadose Zone Environment
AU: * Smith, W A
EM: smitwa@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2203 United States
AU: Cooper, D C
EM: coopdc@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2203 United States
AU: Fox, D T
EM: foxdt@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2203 United States
AU: Plummer, M A
EM: plumma@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2203 United States
AU: Hull, L C
EM: hulllc@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2203 United States
AB: Little is known about how microbial processes affect contaminant transport in the vadose zone (bulk aerobic, nutrient poor, unsaturated). A combination of culture-independent and dependent methods was used to assess prokaryotic community structure in a large, meso-scale column reactor packed with soil from the Idaho National Engineering and Environmental Laboratories in southeast Idaho. Acridine orange direct cell counts, aerobic heterotrophic plate counts, denaturing gradient gel electrophoresis (DGGE), and 16S ribosomal DNA clone libraries were used to characterize the prokaryotic communities at four depths in the column: soil surface, 15cm, 168cm, and 192cm below the surface. No change in total cell count was seen with depth. Aerobic plate counts decreased with depth and number of colony morphologies seen increased from the surface to a depth of 15cm and decreased to 192cm below the soil surface. Extractable DNA concentrations increased between the surface and the 15cm sampling port but remained constant at the remaining depths. Polymerase chain reaction using eubacterial primers provided DNA for DGGE and the clone libraries. DGGE indicated the number of different community members and their relative abundances changed at each depth. Five of the 65 total bands seen were common to all four depths. Clone libraries were constructed for each depth. The number of different clones represented remained relatively constant between depths but the proportions of members present changed. At least 20 different known taxa were represented throughout the column. Aerobic and facultative anaerobic bacteria dominated the surface. A few {\it Clostridia} were also observed, likely as spores since they are obligate anaerobes. The 15cm depth was dominated by {\it Clostridia} and facultative anaerobes. Sulfate reducing bacteria and members of the genus {\it Aquaspirillum}, the genus {\it Flexibacter}, and the phylum {\it Verrucomicrobia} were present at all depths but co-dominated the two lowest depths. These changes in microbial community structure occurred along a gradient of decreasing oxygen and increasing carbon dioxide with depth. M\H{o}ssbauer spectroscopy indicated that iron was lost from the system concomitant with the shift in microbial community structure towards facultative anaerobes. These data indicate that microbial processes within hypoxic microsites may be important in the upper 15cm, and that anaerobic microbial processes in general may be important within this simulated vadose zone environment.
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
DE: 1875 Unsaturated zone
DE: 4803 Bacteria
DE: 4840 Microbiology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting