The effect of long-term mercury pollution on the soil microbial community

Abstract

The effect of long-term exposure to mercury on the soil microbial community was investigated in soil from three different sites along a pollution gradient. The amount of total and bioavailable mercury was negatively correlated to the distance from the center of contamination. The size of the bacterial and protozoan populations was reduced in the most contaminated soil, whereas there was no significant difference in fungal biomass measured as chitinase activity. Based on the number of colony morphotypes, moreover, the culturable bacterial population was structurally less diverse and contained a higher proportion of resistant and fast-growing forms. The profiles of amplified 16S rDNA sequences obtained from community DNA by denaturating gradient gel electrophoresis (DGGE) also reflected the altered community structure and decreased diversity along the mercury gradient as expressed in terms of the number and abundance of bands. The functional potential of the microbial population measured as sole carbon source utilization by Ecoplates((R)) differed between the soils, but there was no change in the number of substrates utilized. The observed changes in the different soil microbial populations are probably a combination of both direct and indirect effects of the mercury contamination.

Impact of copper on the diversity, abundance and transcription of nitrite and nitrous oxide reductase genes in an urban European estuary

“…7); the detrimental effect of Cu occurred through a drastic reduction of denitrifier cells and the transcript diversity of the different genes involved. This subtractive effect by metals on microbial community composition has been identified in other studies (Müller et al , 2001; Holtan‐Hartwig et al , 2002; Kourtev et al , 2009). In our study, because most of the denitrifier community were sensitive to Cu, their contribution to the community was lost, and the ability to denitrify was affected even at the 4 μg Cu g −1 wet wt sediment concentration and was completely disrupted after the addition of 60 μg Cu g −1 wet wt sediment.…”

Adaptation of the bacterial community to mercury contamination

“… A: CFU in soil incubated with 0 (open bars), 2.5 (light grey bars), 10 (dark grey bars) and 25 (black bars) μg Hg(II) g −1 soil. The CFU were grown in 10% LB medium [8] with increasing concentrations of mercury. B: The maximum rate of colour development.…”

“…For bacterial counts (CFU) 1 g of soil was diluted in 9 ml phosphate‐buffered saline [8] and vortexed at maximum velocity for 1 min. Dilutions were made and 100 μl were spread on 10% LB (10× dilution of standard LB) [8] (Merck, Darmstadt, Germany) agar plates supplemented with fungicide (25 μg natamycin ml −1 ) [8] and 0, 0.1, 0.2, 0.4, 0.8, 1.0, 2.5 or 10 μg Hg(II) ml −1 . The number of CFU was recorded after 4 days of incubation at 25°C.…”

Statistical analysis of denaturing gel electrophoresis (DGE) fingerprinting patterns

“…The second approach for a comparative analysis of DGE patterns is based on the whole set of bands present within the profiles. The total number of bands (called sometimes ‘band richness’) in each sample pattern is related to the number of dominant phylotypes, and can be used for comparison purposes (Müller et al., 2001; van der Gucht et al., 2001). Comparison of profiles can be refined by taking into account the relative intensity of each band ( P i ).…”