Use of BIOLOG for the analysis of microbial communities from zinc-contaminated soils

The BIOLOG procedure, a useful method for assessing differences in community structure between sad microbial communities, could be used to determine the impact of metal contamination of soils and reclamation of these soils; however, high metal levels may affect the results of the BIOLOG assay. This project det ermined that Zn in soils interfered with extraction of soils with phosphate buffer by forming an insoluble precipitate. High Zn levels were also shown to prevent color formation and to cause false positive readings in the BIOLOG assay. The objectives of this project were developing and validating a modified BIOLOG method for use in the presence of high Zn concentrations. Substitution of 0.1 M Tris buffer for phosphate buffer prevented precipitate formation during the extraction step; however, extraction with Tris buffer could result in high Zn concentrations in the BIOLOG inoculant. Zinc concentrations of >50 mg L-1 in the inoculant were shown to result in false positive readings due to production of a precipitate in the wells. Raising the pH of the extractant to above 7.0 or removal of the Zn with cation exchange resin relieved this problem. Analyses of BIOLOG data showed that neither raising the extractant pH nor using cation exchange resin resulted in observable changes in BIOLOG metabolic profiles. However, use of Tris buffer in place of phosphate buffer did result in a slight change in BIOLOG metabolic profiles. Thus, the nature of the extracting buffer most be considered when analyzing experimental results. The methods developed herein allow use of the BIOLOG procedure for soils with high metal concentrations.