Investigation of cell exudates active in carbon tetrachloride and chloroform degradation

Contamination of groundwater by chlorinated solvents such as carbon tetrach loride (CCl4) and chloroform (CHCl3) is a widespread problem. The cell exud ates from the methanogen Methanosarcina thermophila are active in the degra dation of CCl4 and CHCl3. This research was performed to characterize these exudates. Examination of the influence of pH indicated that activity was g reater under alkaline conditions. Rapid CCl4 degradation occurred from 35-6 5 degreesC, with first-order degradation rate coefficients increasing as te mperature increased. It was found that proteins were not responsible for CC l4 degradation. The active agents in the cell exudates were <10 kDa in size , with degradation activity present in both 1-10 kDa and <1 kDa size ranges . Upon purification of the <10 kDa size range of the cell exudates on a C-1 8 chromatography column, 17 fractions (out of 100) degraded >50% of the add ed CCl4 in 8 h. These 17 fractions were pooled into three samples based on their elution time from the C-18 column. One of these pooled samples contai ned elevated levels of cobalt, zinc, and iron, at 2, 3, and 13 times the le vels measured in similarly fractionated and pooled samples of medium, respe ctively. The UV-visible spectrum of this pooled sample had an absorption ma ximum at 560-580 nm, which is similar to the absorption maxima of heme (app roximately 550 and 575 nm). The two other pooled samples contained elevated levels of zinc at 11 and 22 times the concentration measured in similarly fractionated and pooled samples of medium, respectively, and also contained very low levels of nickel, cobalt, and iron. This research suggests that t he cell exudates from M. thermophila contain porphorinogen-type molecules c apable of dechlorination, possibly excreted corrinoids, hemes, and zinc-con taining molecules. (C) 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 74; 1 2-17, 2001.