Recovery of heterotrophic soil bacterial guilds from transient gasoline pollution

The response of soil microorganisms to gasoline pollution was determined by comparing bacterial numbers and heterotrophic community diversity between a control site and a site which received a single exposure to unleaded gasoline. Random isolates from samples taken at regular intervals after exposure were clustered into operational taxonomic units based on morphological and physiological characteristics. Bacterial numbers showed an immediate decrease at the experimental site but returned to preexposure levels within two weeks. Diversity, measured by the Shannon-Weaver index, also showed an immediate decrease upon exposure to gasoline but did not return to preexposure levels even after 15 weeks. These results indicate that bacterial numbers alone do not adequately reflect recovery of the microbial community. Furthermore, reestablishment of the preexposure community appears to be a long-term process.