Pyromorphite formation in a fungal biofilm community growing on lead metal.

Lead is a priority pollutant, and lead metal is widely found in the environment as a waterproofing structural component in roofing, fence post covers, venting and flashing, as well as in industrial and urban waste. However, little is known of microbial interactions with metallic lead. The objective of this research was to investigate fungal roles in transformations of lead in a surface biofilm community growing on lead sheeting. The lead surface was found to support a diverse fungal community with several members, such as Aureobasidum pullulans, Phoma macrostoma, Penicillium sp. and Botryotinia fuckeliana, probably originating from adjacent phylloplane communities. Many fungal isolates showed tolerance to lead compounds in growth inhibition assays and were able to mediate production of lead-containing secondary minerals in the presence of metallic lead. These exhibited widely differing morphologies to the lead-containing secondary minerals produced under abiotic conditions. The presence of pyromorphite (Pb5 (PO4 )3 Cl) (approximately 50 wt%) was detected in the lead sheet biofilm, and we speculate that animal (bird) faeces could be a significant source of phosphorus in this location. Pyromorphite formation represents biomineralization of mobile lead species into a very stable form, and this research provides the first demonstration of its occurrence in the natural environment.