Genetic variation and heavy metal tolerance in the ectomycorrhizal basidiomycete Suillus luteus

Abstract

Twenty-one isolates of the ectomycorrhizal fungus Suillus luteus were screened for their tolerance to the heavy metals Zn, Cd, Cu and Ni, measured as inhibition of radial growth and biomass production. Two populations from even-aged pine stands were investigated : 10 isolates were obtained from an area polluted with high levels of Zn, Cd and Cu, and 11 isolates were obtained from a control population located in a nearby unpolluted area. RFLP patterns of the internal transcribed spacer region of the isolates confirmed the morphological identification of the carpophores. All isolates were maintained on basic medium without elevated metals to avoid phenotypically acquired metal tolerance. The in vitro Zn and Cd tolerance of the S. luteus isolates from the polluted habitat were significantly higher than the tolerances measured in the isolates from the nonpolluted site. This observation suggests that the elevated soil metal concentrations might be responsible for the evolution of adaptive Zn and Cd tolerance. Tolerance was maintained in an isolate not exposed to elevated metals for 3 yr. The two S. luteus populations did not differ in tolerance to Cu and Ni. The mechanisms for the adaptive Zn and Cd tolerance are not identical as there was no correlation between response to the two metals ; the most Zn-tolerant isolate was the most sensitive for Cd in the metal-tolerant population. Zinc did not accumulate in basidiocarp tissue, whereas Cd levels in basidiocarps were significantly higher in the population on the polluted site. Inter-simple sequence-repeat fingerprints showed that 90% of the isolates were from different individuals. The genetic variation in the population from the unpolluted site was considerably larger than that observed at the polluted site.

Genetic diversity and differential in vitro responses to Ni in Cenococcum geophilum isolates from serpentine soils in Portugal

“…Blaudez et al (2000) investigated the response of isolates of Paxillus involutus, Pisolithus tinctorius, Suillus bovinus, S. variegatus, and S. luteus to Cd, Co, Ni, and Zn and found no significant differences between EC 50 values of isolates from different soil categories (low, medium, or high metal concentration). By contrast, however, Colpaert et al (2000) reported that isolates of S. luteus from a site polluted with Zn and Cd were more tolerant to these metals than isolates from an unpolluted site. Therefore, it seems that tolerance to heavy metals in ECM fungi can be either constitutive or adaptive.…”

“…Significant inter-and intraspecific variation in sensitivity to heavy metals by ECM fungi has been extensively reported Van Assche 1987, 1992;Denny and Wilkins 1987;Jones and Hutchinson 1988;EgertonWarburton and Griffin 1995;Hartley et al 1997;Blaudez et al 2000;Colpaert et al 2000). For example, the EC 50 (i.e., the effective concentration of metal that inhibits growth by 50%) values for Cd differed by over three orders of magnitude among the four ECM species studied by Hartley et al (1997).…”

“…After incubation, mycelia were harvested to determine their biomass. Agar was removed according to Colpaert et al (2000), and the colonies were dried to a constant mass at 60°C and weighed. A tolerance index (TI) for both radial growth rate (mm/week) and final biomass (mg) was calculated as the percentage of the radial growth rate (or biomass) retained on the Ni-amended media compared with performance on the control medium (Colpaert and Van Assche 1987).…”

“…In turn, Blaudez et al (2000) reported wide variation in Cd sensitivity among isolates of different ECM species, with EC 50 values of Suillus luteus isolates ranging from 0.04 to > 1 ppm. Several studies have compared the response of ECM isolates of the same species from contaminated and uncontaminated sites in an attempt to relate the degree of sensitivity to specific metals with the concentration of those metals in the soil of origin (Brown and Wilkins 1985;Denny and Wilkins 1987;Jones and Hutchinson 1988;Van Assche 1987, 1992;Egerton-Warburton and Griffin 1995;Blaudez et al 2000;Colpaert et al 2000). Blaudez et al (2000) investigated the response of isolates of Paxillus involutus, Pisolithus tinctorius, Suillus bovinus, S. variegatus, and S. luteus to Cd, Co, Ni, and Zn and found no significant differences between EC 50 values of isolates from different soil categories (low, medium, or high metal concentration).…”

Transcriptome analysis by cDNA-AFLP of Suillus luteus Cd-tolerant and Cd-sensitive isolates

“…), an ectomycorrhizal basidiomycete, is a typical pioneer fungus in primary forest succession. It is a common root symbiont of young pine trees (Pinus sylvestris) and evolves metal-tolerant ecotypes on heavy metal contaminated sites (Colpaert et al 2000). Its basidiospores are most likely dispersed by wind and mammals (Ashkannejhad and Horton 2006), and its frequent and early sexual reproduction with the release of billions of basidiospores are a trade mark of its pioneer behaviour and may favour rapid selection for genotypes adapted to specific soil conditions.…”