Interaction between tolerance and 70 kDa stress protein (hsp70) induction in collembolan populations exposed to long-term metal pollution

Abstract

Induction of the 70 kDa stress proteins (hsp70) as a marker for cellular stress response was investigated in two species of Collembola from a metal concentration gradient near a brass mill in the vicinity of Gusum, Sweden. In the field, populations of Orchesella bifasciata (Nicolet 1841) in the middle of the gradient, which ranged from about 60 to 3800 mg of Zn+Cu per kg dry wt. litter, had 40% higher hsp70 levels than populations from the least and most contaminated sites, but differences were not significant. All but one of the populations, inhabiting a severely polluted area, approached lower hsp70 values when they were fed algae containing very high metal concentrations; the hsp70 level in specimens from the control site exposed to polluted algae was below the detection limit, most probably due to pathological cell damage. The hsp70 levels in specimens from contaminated sites with the highest in situ hsp70 levels could not be distinguished from those of control site individuals after they were reared on litter from the control site, and the hsp70 level of control site individuals increased by nearly 100% when they were reared on litter from one of the contaminated sites. Tomocerus flavescens (Tullberg 1871) had higher hsp70 levels than O. bifasciata at the contaminated sites but responded similarly to the experimental treatments. A model is presented to interpret the observations as the result of the dual role of hsp70 to maintain cellular protein homeostasis and to stabilise protein folding in metal tolerant specimens. Differences in tolerance between individuals and heterogeneous distribution of metals in the litter may account for the large intraspecific variability found in hsp70 levels.