Effects of temperature on metal tolerance and the accumulation of Zn and Pb by metal-tolerant fungi isolated from urban runoff treatment wetlands

To investigate the ability of two fungi to accumulate Zn and Pb, the effect of temperature on their metal tolerance and possible mechanisms involved in metal accumulation. Beauveria bassiana and Rhodotorula mucilaginosa isolated from constructed wetlands receiving urban runoff were grown in modified glycerol asparagine medium containing elevated levels of Zn and Pb at 30 degrees C. Beauveria bassiana accumulated up to 0.64% of available Zn and 8.44% of Pb. The corresponding values for R. mucilaginosa were up to 2.05% for Zn and 16.55% for Pb. Radial growth of colonies grown at 4 degrees and 30 degrees C on agar containing Zn or Pb indicated that metal tolerance was not seriously affected by a decrease in temperature. Transmission electron microscopy and emission dispersion x-ray spectrophotometry suggested that the mechanism of resistance in B. bassiana may be associated with the precipitation of Pb (possibly in the form of oxalates). The processes of biosorption could potentially occur throughout the year with both living and dead cells able to accumulate metals. Identified precipitation processes could be an important mechanism in metal removal in wetland substrates serving as long-term storage sinks.