Applied and Environmental Microbiology, October 2001, p. 4619-4629, Vol. 67, No. 10
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.10.4619-4629.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Section of Molecular Microbial Ecology, Department of Molecular Cell Physiology, Faculty of Biology, Research School SENSE,1 and Department of Hydro(geo)logy, Faculty of Earth Sciences,2 Vrije Universiteit, NL-1081 HV Amsterdam, The Netherlands
Received 29 January 2001/Accepted 13 July 2001
Knowledge about the relationship between microbial community
structure and hydrogeochemistry (e.g., pollution, redox and
degradation processes) in landfill leachate-polluted aquifers is
required to develop tools for predicting and monitoring natural
attenuation. In this study analyses of pollutant and redox chemistry
were conducted in parallel with culture-independent profiling of
microbial communities present in a well-defined aquifer
(Banisveld, The Netherlands). Degradation of organic contaminants
occurred under iron-reducing conditions in the plume
of pollution, while upstream of the landfill and above the plume
denitrification was the dominant redox process. Beneath
the plume iron reduction occurred. Numerical comparison of 16S
ribosomal DNA (rDNA)-based denaturing gradient gel
electrophoresis (DGGE) profiles of Bacteria and
Archaea in 29 groundwater samples revealed a
clear difference between the microbial community structures inside
and outside the contaminant plume. A similar relationship was
not evident in sediment samples. DGGE data were supported by
sequencing cloned 16S rDNA. Upstream of the landfill members of the
subclass of the class Proteobacteria
(
-proteobacteria) dominated. This group was not encountered
beneath the landfill, where gram-positive bacteria dominated.
Further downstream the contribution of gram-positive bacteria to the
clone library decreased, while the contribution of
-proteobacteria strongly increased and
-proteobacteria
reappeared. The
-proteobacteria (Acidovorax, Rhodoferax) differed considerably from those found upstream
(Gallionella, Azoarcus). Direct comparisons of
cloned 16S rDNA with bands in DGGE profiles revealed that the data from
each analysis were comparable. A relationship was observed
between the dominant redox processes and the bacteria identified. In
the iron-reducing plume members of the family
Geobacteraceae made a strong contribution to the microbial communities. Because the only known aromatic
hydrocarbon-degrading, iron-reducing bacteria are
Geobacter spp., their occurrence in landfill
leachate-contaminated aquifers deserves more detailed consideration.
Present address: Fossil Fuels and Environmental Geochemistry
Post-Graduate Institute, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, United Kingdom.
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