Microbial release of sulphur ions from atmospheric pollution deposits.
The surface of leaves of Acer pseudoplatanus growing in areas exposed to heavy atmospheric pollution are covered with atmospheric pollution deposits (APD). Scanning electron microscopy revealed micro-organisms growing in intimate association with these deposits. The deposits contained sufficient carbon and nitrogen to support growth of Fusarium solani in culture and in autoclaved and non-sterilized soils, and sufficient reduced sulphur for the in vitro growth of Thiobacillus thioparus. When T. thioparus and F. solani were grown in medium supplemented with APD as sole carbon and nitrogen sources, increases in the concentrations of soluble S2O32-, S4O62- and SO42- resulted. Similar increases occurred when APD was added to complete fungal growth medium. Increases in LiCl2-extractable sulphur ions occurred in fresh soil amended with APD, and in autoclaved soils containing APD and inoculated with spores of F. solani. Arylsulphatase activity increased in fresh soils and in soils autoclaved and inoculated with F. solani when APD was added, implicating sulphur mineralization, as well as sulphur oxidation, in the release of sulphur ions from APD. Microbial release of sulphur ions from APD can account in part for the increased concentrations of sulphur ions in heavily atmospheric-polluted soils.