Effects of various environmental conditions on the transformation of chlorinated solvents by Methanosarcina thermophila cell exudates

Several microbiologically produced biomolecules have been shown to degrade chlorinated contaminants found in groundwater systems. It was discovered th at the cell-free exudates of the methanogen Methanosarcina thermophila were capable of carbon tetrachloride (CT) and chloroform (CF) degradation. Char acterization of the exudates suggested that the active agents were porphori nogen-type molecules, possibly containing zinc. This research was performed to determine if the exudates from M. thermophila could be used for remedia tion purposes. The cell exudates were found to be capable of degrading CT, CF, tetrachloroethene, trichloroethene, and 1,1,1-trichloroethane. CT degra dation was used to gauge exudate activity under a variety of conditions tha t would be encountered in the environment. The cell exudates were active wh en incubated in two types of soil matrices and at temperatures ranging from 4 to 23 degreesC. Over a 35-day period approximately 10.2 mu moles of CT w ere degraded by M. thermophila exudates. To test the hypothesis that the ex udates contained either a zinc porphorinogen or a quinone, experiments were performed with zinc 5,10,15,20-tetra (4-pyridyl)-21 H, 23 H-porphine tetra kis, protoporphyrin IX zinc, and juglone. The two zinc porphyrins were capa ble of mediating CT degradation at rates comparable to those observed with the M. thermophila exudates; however, juglone was only capable of very slow CT transformation. The electron-transfer activity of the M. thermophila ce ll exudates was therefore more consistent with the activity of porphorinoge ns rather than quinones. Finally, in two enrichment cultures established fr om aquifer material and marine sediment, the possibility of excreted agents capable of degrading CT was evident. (C) 2001 John Wiley & Sons, Inc.