Stress response in two strains of the aquatic hyphomycete Heliscus lugdunensis after exposure to cadmium and copper ions Bianca Braha 1 , Herbert Tintemann 1 , Gudrun Krauss 2 , Jim Ehrman 3 , Felix Ba¨rlocher 3 & Gerd-Joachim Krauss 1, * 1 Department of Biochemistry/Biotechnology, Division of Ecological and Plant Biochemistry, Martin-Luther- University, Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle/Saale, Germany; 2 Department of Environ- mental Microbiology, UFZ Centre for Environmental Research Leipzig-Halle in the Helmholtz Association, Theodor-Lieser-Str. 4, 06120, Halle/Saale, Germany; 3 Department of Biology, Mount-Allison-University, Sackville, NB, E4L 1G7, Canada; *Author for correspondence (E-mail: krauss@biochemtech.uni-halle.de) Received 7 June 2005; accepted 19 May 2006 Key words: aquatic hyphomycetes, Heliscus lugdunensis, glutathione, cadmium, copper Abstract Biochemical responses to cadmium (Cd 2+ ) and copper (Cu 2+ ) exposure were compared in two strains of the aquatic hyphomycete (AQH) Heliscus lugdunensis. One strain (H4-2-4) had been isolated from a heavy metal polluted site, the other (H8-2-1) from a moderately polluted habitat. Conidia of the two strains differed in shape and size. Intracellular accumulation of Cd 2+ and Cu 2+ was lower in H4-2-4 than in H8-2-1. Both strains synthesized significantly more glutathione (GSH), cysteine (Cys) and c-glutamylcysteine (c-EC) in the presence of 25 and 50 lM Cd 2+ , but quantities and rates of synthesis were different. In H4-2-4, exposure to 50 lM Cd 2+ increased GSH levels to 262% of the control; in H8-2-1 it increased to 156%. Mycelia of the two strains were analysed for peroxidase, dehydroascorbate reductase, glutathione reductase and glucose-6-phosphate dehydrogenase. With Cd 2+ exposure, peroxidase activity increased in both strains. Cu 2+ stress increased dehydroascorbate reductase activity in H4-2-4 but not in H8-2-1. Dehydroascorbate reductase and glucose-6-phosphate dehydrogenase activities progressively declined in the presence of Cd 2+ , indicating a correlation with Cd 2+ accumulation in both strains. Cd 2+ and Cu 2+ exposure decreased glutathione reductase activity. Abbreviations: GSH – reduced glutathione; GSSG – oxidized glutathione; c-EC – c-glutamylcysteine; POD – peroxidase; DHR – dehydroascorbate reductase; GR – glutathione reductase; G6PD – glucose- 6-phosphate dehydrogenase Introduction High levels of heavy metals in the environment are associated primarily with anthropogenic activities. This type of pollution generally lowers biodiversity in terrestrial and aquatic ecosystems (Prasad 2001), but many bacteria and fungi have evolved the ability to live in such stressful habitats (Lovley 2000). To survive metal exposure in their natural environment, bacteria and fungi have developed a number of resistance mechanisms (Lovley 2000; Mills 2002). Fungi can sequester, mobilize, or transform various ions (Gadd 2001; Gadd & Sayer 2000) and thereby control the biogeochemical mobility and behaviour of metals in aquatic envi- ronments. These microbial features might be exploited for reducing the environmental impact of mine waste (Gadd 2001; Rawlings 2002). Potential BioMetals (2007) 20:93–105 Ó Springer 2006 DOI 10.1007/s10534-006-9018-y