Changes in the biofilm microflora of limestone caused by atmospheric pollutants

Historic limestone materials in urban environments are continually exposed to air pollutants, including sulfur compounds and hydrocarbons. We investig ated the effects of air pollution on the biofilm microflora of historic lim estone gravestones located at two locations Massachusetts, USA. Our data sh owed that the culturable populations of chemolithotrophic and heterotrophic bacteria, and fungi were suppressed in the polluted habitat comparing with the unpolluted location. The diversity of the microflora was also reduced in the surface biofilms on gravestones in thr city contaminated by air poll ution. However, both the sulfur-oxidizing and hydrocarbon-utilizing microfl ora were enriched in the biofilms exposed to air pollution. In a laboratory study, low concentrations of the polluting chemicals stimulated growth of these bacteria, and resulted in rapid acid production. Scanning electron mi croscopy demonstrated that the biofilms of both the sulfur-oxidizing bacter ia and the hydrocarbon-degrading microflora penetrated into the limestone. The enrichment of sulfur and hydrocarbon-utilizing bacteria in the biofilms may contribute to dissolution of the stone. However, further research is r equired to determine the effects of specific metabolites of these microorga nisms on stone deterioration. (C) 2001 Published by Elsevier Science Ltd.