Cumulative effects of short-term polymetal contamination on soil bacterial community structure

Abstract

In this study we evaluated the short-term effects of copper, cadmium, and mercury, added singly or in combination at different doses, on soil bacterial community structure using the bacterial automated ribosomal intergenic spacer analysis (B-ARISA) fingerprinting technique. Principal-component analysis of B-ARISA profiles allowed us to deduce the following order of impact: (Cu + Cd + Hg) >> Hg > or = Cd > Cu. These results demonstrated that there was a cumulative effect of metal toxicity. Furthermore, the trend of modifications was consistent with the "hump-backed" relationships between biological diversity and disturbance described by Giller et al. (K. E. Giller, E. Witler, and S. P. McGrath, Soil Biol. Biochem. 30:1389-1414, 1998).

FIG. 1.

B-ARISA profiles obtained at day 60 with DNA extracted from triplicate microcosms treated with water (control) and with copper (Cu), cadmium (Cd), mercury (Hg), and all three metals (Cu + Hg + Cd) at HC.

FIG. 2.

PCA ordination of the bacterial genetic structure for microcosms contaminated with copper (A), cadmium (B), mercury (C), and all three metals (Cu + Hg + Cd) (D) at LC (panels I), MC (panels II), and HC (panels III). The statistical ellipses indicate 90% confidence for replicates. Open ellipses, zero time (T0); light gray ellipses, day 10 (T10); dark gray ellipses, day 60 (T60).

FIG. 3.

PCA ordination of the bacterial genetic structure for the different levels of copper (A), cadmium (B), mercury (C), and trimetal (D) contamination at day 60. The statistical ellipses indicate 90% confidence. Open ellipses, control microcosms (H₂O); light gray ellipses, LC; dark gray ellipses, MC; striped ellipses, HC.

FIG. 4.

PCA ordination of the bacterial genetic structure for control microcosms (open ellipses) and microcosms contaminated with copper (light gray ellipses), cadmium (dark gray ellipses), mercury (black ellipses), and all three metals (striped ellipses) at MC (A) and HC (B) at day 60. The statistical ellipses indicate 90% confidence.