Hydrobiologia 346: 77–84, 1997. 77 c 1997 Kluwer Academic Publishers. Printed in Belgium. Effects of cadmium, copper, and zinc on growth and thiol content of aquatic hyphomycetes J¨ urgen Miersch 1 , Felix B¨ arlocher 2 , Ina Bruns 1 & Gerd-Joachim Krauss 1 1 Martin-Luther-University Halle-Wittenberg, Institute of Biochemistry, 06099 Halle/S., Germany 2 Mount Allison University, Biology Department, Sackville, N.B., E0A 3C0, Canada Received 27 June 1996; in revised form 19 February 1997; accepted 26 February 1997 Key words: aquatic hyphomycetes, heavy metals, sulfur-rich compounds, metallothioneins Abstract The effects of cadmium, copper, and zinc on the growth of ten strains of aquatic hyphomycetes were investigated. On a solid medium, Cd and Cu reduced radial growth of most strains by 50% at concentrations between 150–400 M; in a liquid medium, the strains were more sensitive. The inhibitory effects of zinc were much less severe. Two isolates (Articulospora tetracladia and Tetracladium marchalianum) from a copper-mine stream were more resistant against copper than conspecific strains from a non-polluted stream. Heliscus lugdunensis and Varicosporium elodeae responded to Cd exposure, but not to Cu or Zn exposure, by increased synthesis of SH-containing compounds. Glutathione levels showed a unimodal response to increasing Cd and Zn exposure. With copper, glutathione decreased at intermediate levels of contamination. In the presence of Cd, H. lugdunensis synthesized several unknown sulfur-rich substances that were absent or produced at reduced rates in control cultures. Introduction Pollution by heavy metals can have serious environ- mental consequences. These compounds are intro- duced into ecosystems through mining, industrial emissions, garbage disposal, and as byproducts of agri- cultural fertilizers (Merian, 1991). Their bioavailabil- ity depends crucially on the solubility of the various ionic species (Scheffer & Schachtschabel, 1989). In order to express their toxicity, which inhibits growth in plants, animals and microorganisms, heavy metals generally have to enter living cells (Arnebrant et al., 1987; Rauser, 1990; Steffens, 1990; Ernst et al., 1992; Schat & Kalff, 1992). There are only a few isolated studies of heavy metal uptake and accumulation by fungi. It has been demonstrated, for example, in some aquatic fungi (Duddridge & Wainwright, 1980; Abel & B¨ arlocher, 1984), in the yeast (Saccharomyces cere- visiae), in Aspergillus niger (Huang et al., 1991) and a few other species (Winkelmann & Winge, 1994). Many organisms have evolved tolerance toward heavy metals (Ernst, 1974; Verkleij & Schat, 1990; Robinson et al., 1993). As a consequence they can accumulate high concentrations of these metals with- out suffering any deleterious effects. This has been demonstrated in terrestrial plants, e.g. in Bryophytes (Markert, 1993), Silene spp. (Lolklema et al., 1984), tomato cell culture (Neumann et al., 1994), aquatic plants (algae, mosses and vascular plants, Siebert et al., 1995) and fungi (Gadd, 1993). Generally, organisms react to increased heavy metal exposure by synthe- sizing sulfur-rich compounds, particularly metalloth- ioneins of the classes 1–3 (Fowler et al., 1987; Rauser, 1990; Robinson et al., 1993). In animals, these include cysteine-rich peptides 4 of class 1 (MT-1), while in plants metallothioneins of classes 2 and 3 (MT-2 and MT-3) predominate. The latter (MT-3) are often called phytochelatins (Fowler et al., 1987; Ernst et al., 1992; Rauser, 1993). Their biosynthesis is closely related to glutathione metabolism (Grill et al., 1989). The goal of the current study was to evaluate the effects of cadmium, copper and zinc on growth of, and induction of small sulfur-containing peptides in, aquatic hyphomycetes, a group of fungi playing an important role as intermediaries between plant detri- tus and invertebrates in streams (B¨ arlocher, 1992). To