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Appl. Environ. Microbiol., Feb 1996, 420-428, Vol 62, No. 2
T Pennanen, A Frostegard, H Fritze and E Baath
The effects of long-term heavy metal deposition on microbial community
structure and the level of bacterial community tolerance were studied along
two different gradients in Scandinavian coniferous forest soils. One was
near the Harjavalta smelter in Finland, and one was at Ronnskar in Sweden.
Phospholipid fatty acid (PLFA) analysis revealed a gradual change in soil
microbial communities along both pollution gradients, and most of the
individual PLFAs changed similarly to metal pollution at both sites. The
relative quantities of the PLFAs br18:0, br17:0, i16:0, and i16:1 increased
with increasing heavy metal concentration, while those of 20:4 and
18:2(omega)6, which is a predominant PLFA in many fungi, decreased. The
fungal part of the microbial biomass was found to be more sensitive to
heavy metals. This resulted in a decreased fungal/bacterial biomass ratio
along the pollution gradient towards the smelters. The thymidine
incorporation technique was used to study the heavy metal tolerance of the
bacteria. The bacterial community at the Harjavalta smelter, exposed mainly
to Cu deposition, exhibited an increased tolerance to Cu but not to Cd, Ni,
and Zn. At the Ronnskar smelter the deposition consisting of a mixture of
metals increased the bacterial community tolerance to all tested metals.
Both the PLFA pattern and the bacterial community tolerance were affected
at lower soil metal concentrations than were bacterial counts and bacterial
activities. At Harjavalta the increased Cu tolerance of the bacteria and
the change in the PLFA pattern of the microbial community were found at the
same soil Cu concentrations. This indicated that the altered PLFA pattern
was at least partly due to an altered, more metal-tolerant bacterial
community. At Ronnskar, where the PLFA data varied more, a correlation
between bacterial community tolerance and an altered PLFA pattern was found
up to 10 to 15 km from the smelter. Farther away changes in the PLFA
pattern could not be explained by an increased community tolerance to
metals.
Copyright © 1996, American Society for Microbiology
Phospholipid Fatty Acid Composition and Heavy Metal Tolerance of Soil Microbial Communities along Two Heavy Metal-Polluted Gradients in Coniferous Forests
Finnish Forest Research Institute, 01301 Vantaa, Finland, and Department of Microbial Ecology, Lund University, 22362 Lund, Sweden
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