Filtration of Bacillus subtilis and Bacillus cereus spores in a pyroclastic topsoil, carbonate Apennines, southern Italy.

A comparative study on the filtration of Bacillus subtilis and Bacillus cereus spores in a pyroclastic topsoil was performed in laboratory using surfactant-free solutions and solutions with the surfactant sodium dodecyl sulphate (SDS) (anionic). The results of the column experiments demonstrate that the SDS does not significantly influence the retention of both B. subtilis and B. cereus spores. Since the SDS is adsorbed through hydrophobic interaction with the organic matter of soil media, these results suggest that hydrophobic interaction between spores and organic matter does not play a significant role on filtration processes within the studied topsoil. This statement is of utmost importance taking into consideration the hydrophobic nature of Bacillus spores and the very high organic matter content in the studied topsoil (20-34%). Conversely, the retention of the analyzed spores seems to be influenced by the pore size exclusion phenomenon.