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

Abstract

Several microbiologically produced biomolecules have been shown to degrade chlorinated contaminants found in groundwater systems. It was discovered that the cell-free exudates of the methanogen Methanosarcina thermophila were capable of carbon tetrachloride (CT) and chloroform (CF) degradation. Characterization of the exudates suggested that the active agents were porphorinogen-type molecules, possibly containing zinc. This research was performed to determine if the exudates from M. thermophila could be used for remediation purposes. The cell exudates were found to be capable of degrading CT, CF, tetrachloroethene, trichloroethene, and 1,1,1-trichloroethane. CT degradation was used to gauge exudate activity under a variety of conditions that would be encountered in the environment. The cell exudates were active when incubated in two types of soil matrices and at temperatures ranging from 4 to 23 degrees C. Over a 35-day period approximately 10.2 micromoles of CT were degraded by M. thermophila exudates. To test the hypothesis that the exudates 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 tetrakis, protoporphyrin IX zinc, and juglone. The two zinc porphyrins were capable 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 cell exudates was therefore more consistent with the activity of porphorinogens rather than quinones. Finally, in two enrichment cultures established from aquifer material and marine sediment, the possibility of excreted agents capable of degrading CT was evident.

In Situ Dechlorination of TCE during Aquifer Heating

“…The temperature optimum for the enrichment culture in their study was 60°C to 65°C. Extracellular biomolecules of Methanosarcina thermophilia have been shown to dechlorinate carbon tetrachloride (Baeseman and Novak 2001; Andrews and Novak 2001; Novak et al 1998a, 1998b), and dechlorination occurs with increasing rates up to a temperature of about 65°C (Koons et al 2001).…”

Microbial degradation of tetrachloromethane: mechanisms and perspectives for bioremediation

“…Different compounds display variable efficiencies in CCl 4 degradation. The coenzyme F430 of methyl coenzyme M reductase (Rouvière & Wolfe, 1988; Novak et al , 1998a, b; Baeseman & Novak, 2001; Koons et al , 2001), involved in a late step of methanogenesis, catalyzed the degradation of CCl 4 (2.2 mM) at a molar ratio of 0.02 for F430 to CCl 4 (Krone et al , 1989). A similar molar ratio of 0.04 for vitamin B 12 to CCl 4 enabled the reductive degradation of CCl 4 (100 nM) (Assaf‐Anid et al , 1994).…”

“…For example, supplementation of growth medium with porphobilinogen, a de novo vitamin B 12 biosynthesis precursor of the corrin ring of cobalamin, enhanced CCl 4 biodegradation in methanogenic cultures fed with methanol (Guerrero‐Barajas & Field, 2006). Methanogens in particular produce more than one catalytic factor in CCl 4 degradation: corrinoids, factor F430, one or more zinc porphyrins and b ‐ and c ‐type cytochromes (Krone et al , 1989; Baeseman & Novak, 2001). Increased CCl 4 degradation was concomitant with increased basal cobalamin production and factor F430 levels in the methanogen M. barkeri (Mazumder et al , 1987; Van Eekert et al , 1998).…”

Metagenomic- and cultivation-based exploration of anaerobic chloroform biotransformation in hypersaline sediments as natural source of chloromethanes

“…(25), methanogenic Methanosarcina spp. (26–28), and fermentative Pantoea spp. (23) producing dichloromethane (DCM), carbon monoxide (CO) and/or carbon dioxide (CO 2 ).…”