Cd-tolerant arbuscular mycorrhizal (AM) fungi from heavy-metal polluted soils

Abstract

Spores of arbuscular mycorrhizal (AM) fungi were isolated from two heavy-metal polluted soils in France via trap culture with leek (Allium porrum L.). Preliminary identification showed that the predominant spore type of both cultures (P2 and Cd40) belongs to the Glomus mosseae group. Their sensitivity to cadmium was compared to a laboratory reference strain (G. mosseae) by in vitro germination tests with cadmium nitrate solutions at a range of concentrations (0 to 100mg L -1) as well as extracts from a metal-polluted and unpolluted soils. Both cultures of AM fungi from heavy-metal polluted soils were more tolerant to cadmium than the G. mosseae reference strain. The graphically estimated ECs0 was 0.8mg L -1 Cd (concentration added to the test device) for G. mosseae and 7mg L -1 for P2 culture, corresponding to effective Cd concentrations of approximately 50-70 Ixg L 1 and 200-500 Ixg L 1, respectively. The extract of the metal-polluted soil P2 decreased germination of spores from the reference G. mosseae but not from P2 culture. However, the extracts of two unpolluted soils with different physico-chemical characteristics did not affect G. mosseae, whereas germination of P2 spores was markedly decreased in the presence of one of the extracts. These results indicate a potential adaptation of AM fungi to elevated metal concentrations in soil. The tested spores may be considered as metal-tolerant ecotypes. Spore germination results in presence of soil extracts show the difficulty of assessing the ecotoxic effect of metals on AM fungi without considering other soil factors that may interfere in spore germination and hyphal extension.

Effects of AM colonization on “wild tobacco” plants grown in zinc-contaminated soil

“…It is possible that G. intraradices and G. mosseae are 13 tolerant to Zn and Cd soil excess, a property that has been described for Cd-tolerant G. mosseae found at heavy-metal polluted sites (Weissenhorn et al 1993). A number of studies have reported that AM colonization can increase the uptake of Zn and other trace minerals by host plants (Davies 1987, Gildon & Tinker 1983); yet few studies have observed the induction of AM root colonization when Zn is in excess.…”

“…Recent phytoremediation studies that incorporated the AM-variable have had mixed findings. Some studies have shown that AM colonization increases the uptake and accumulation of heavy metals in host plants (Davies et al 2001(Davies et al , 2002Hovsepyan & Greipsson 2004;Rufyikiri et al 2002Rufyikiri et al , 6 2003, while others suggested that AM fungi exude enzymes that participate in the immobilization process of soil contaminants, in which case accumulation in plants is reduced (Joner et al 2000, Weissenhorn et al 1993). …”

Uptake of cadmium from an experimentally contaminated calcareous soil by arbuscular mycorrhizal maize ( Zea mays L.)

“…Weissenhorn et al (1993) demonstrated stronger tolerance to Cd in AM fungal strains isolated from heavy metal-polluted soils. The potential use of AM fungi in remediation programs for metal-contaminated ecosystems has recently been proposed (Vangronsveld et al 1996;Khan et al 2000;Leyval et al 2002).…”

“…Although the initial plant colonizers of heavy metal-contaminated sites are often species tolerant to extreme conditions and tend to be nonmycorrhizal (Shetty et al 1994), they may increase soil organic matter content, modify the soil microclimate and promote conditions conducive to the establishment of species with stronger mycorrhizal dependence . Mycorrhizas have recently been reported in plants growing on heavy metal-contaminated sites (Shetty et al 1995;Weissenhorn and Leyval 1995;Pawlowska et al 1996;Chaudhry et al 1999), and metal-tolerant fungal strains have been isolated (Griffioen 1994;Weissenhorn et al 1993Weissenhorn et al , 1994Hildebrandt et al 1999). Alleviation of heavy metal phytotoxicity by arbuscular mycorrhiza has been indicated in several studies (Schüepp et al 1987;Heggo et al 1990;Zhu et al 2001;Chen et al 2003).…”

Fungos micorrízicos arbusculares em solos de área poluída com metais pesados

“…Por essa razão, os fungos micorrízicos arbusculares (FMAs) e a simbiose micorrízica em solos poluídos têm sido objeto de diversos estudos em várias regiões do mundo (Gildon & Tinker, 1981;Ernst et al, 1984;Walker et al, 1984;Koske & Walker, 1986;Bethlenfalvay & Franson, 1989;Ietswaart et al, 1992;Christie & Kilpatrick, 1992;Sambandan et al, 1992;Raman et al, 1993;Weissenhorn et al, 1993;Griffiöen, 1994;Noyd et al, 1995;Pawlowska et al, 1996).…”