The effect of metals on growth, reproduction and attachment of zoosporic true fungi

Abstract

Zoosporic fungi (chytrids) are common within soils. Chytrids contribute to the soil carbon cycle by converting complex carbohydrates to more accessible forms and are also important in biogeochemical cycling of nitrogen and sulphur. However, the roles of chytrids in many soil processes, and their responses to environmental stress, are not well understood. In order to explore the response of chytrids to temperature stress, here we initially examine the effect of increased temperature on chytrid isolates from different geographic and climatic regions. Isolates of Gaertneriomyces semiglobifer from different regions grow at similar rates and have similar patterns of zoospore production at different temperatures. This data allows prediction of the distribution, growth and abundance of the fungus and potential changes due to the effects of climate change. We then examine the effect of the toxic metals Cu (ll), Pb (ll) and Zn (ll) on growth, zoospore production and attachment of chytrids to common organic substrates. The four isolates, representing four orders within the phylum Chytridiomycota, showed greatest sensitivity in growth, attachment and zoospore production in response to Cu (ll) and least sensitivity to Pb (ll). Interestingly, some metals also caused increases in growth, zoospore production and attachment below the toxic threshold concentrations. In particular, Rhizophlyctis rosea increased the number and length of rhizoids when incubated with Pb (ll). Chytrids are known to be widespread and common throughout soils world-wide. Our work allows us to predict that the levels of Cu (ll), Pb (ll) and Zn (ll), found here to be toxic, will be detrimental to soil chytrid populations and reduce colonisation of organic substrates. Toxic effects of metals on the lifecycle of chytrids are expected to reduce the rate of mineralisation of soil organic matter, thereby reducing nutrient availability for the soil microbial loop, to the detriment of ecological function in soils.