Microbial ecology of a creosote-contaminated aquifer at St. Louis Park, Minnesota

Abstract

Bacterial populations were sampled in creosote-contaminated and undisturbed zones of the anaerobic, surficial Middle Drift aquifer at St. Louis Park, Minnesota. The densities of several types of bacteria including total aerobes, total anaerobes, nitrate-respirers, and iron-reducers were about the same in the contaminated and undisturbed zones. Chemical analyses suggested that nitrate-respiration and iron-reduction were occurring in the contaminated zone. Conversion of phenolic compounds to methane occurred in the contaminated zone. Methanogenic bacteria were found only in the contaminated zone. In laboratory culture, methane was evolved when contaminated groundwater was inoculated with bacteria from the contaminated zone. Obligate anaerobic bacteria isolated from laboratory reactors include: a methanosarcina; a short methanobacterium; and a longer, crooked methanobacterium. Pseudomonas stutzeri, a nitrate-respiring bacterium, was isolated from both the laboratory reactors and the contaminated zone of the aquifer. These Ps. stutzeri strains used phenol as an electron source for nitrate reduction. The methanogenic consortium found in the laboratory reactor appears similar to those described in other studies of the methanogenic fermentation of aromatic compounds. 21 references, 3 figures, 3 tables.