Transformation of carbon tetrachloride by Pseudomonas sp. strain KC under denitrification conditions

Abstract

A denitrifying Pseudomonas sp. (strain KC) capable of transforming carbon tetrachloride (CT) was isolated from groundwater aquifer solids. Major products of the transformation of "4C-labeled CT by Pseudomonas strain KC under denitrification conditions were "4CO2 and an unidentified water-soluble fraction. Little or no chloroform was produced. Addition of dissolved trace metals, notably, ferrous iron and cobalt, to the growth medium appeared to enhance growth of Pseudomonas strain KC while inhibiting transformation of CT. It is hypothesized that transformation of CT by this organism is associated with the mechanism of trace-metal scavenging. Microbial capabilities for dehalogenation are widely distributed in nature. This activity could potentially be exploited for in situ bioremediation of contaminated groundwater. The use of denitrifying organisms would be advantageous for aquifer bioremediation because, unlike oxygen, nitrate and nitrous oxide are highly soluble in water and easily added. Furthermore, nitrate is already present in many groundwaters because of the widespread use of fertilizers. Bouwer and McCarty (2) demonstrated that carbon tetrachloride (CT) and brominated trihalomethanes are transformed under mixed-culture denitrifying conditions. To date, however, there are no reports of pure-culture denitrifiers capable of haloaliphatic transformations. This has led some to speculate that nondenitrifying "secondary" organisms are responsible for biotransformations observed in mixed cultures under denitrification conditions (5). To assess the possibility that subsurface denitrifiers might possess fortuitous dehalogenating capability, several denitrifying enrichments were prepared with aquifer solids as the source of microorganisms. Aquifer materials were obtained from sites in Seal Beach, Calif.; Moffett Field, Calif.; and Savannah River, Ga. These enrichments were screened for their activity toward CT. This screening culminated in the successful isolation of Pseudomonas sp. strain KC, an organism that rapidly and completely degrades CT, with carbon dioxide as its major end product. Several nondenitrifying organisms are also known to transform CT, but the products (chloroform and dichloromethane) are undesirable, and the rates of transformation can be slow. The metabolic basis for the transformation of CT by Pseudomonas strain KC was explored as this transformation may suggest a means for controlling reductive transformations in biological systems so as to produce innocuous products. MATERIALS AND METHODS Chemicals. CT (99+% pure) was obtained from Aldrich Chemical Co., Milwaukee, Wis. Chloroform (CF; Baker analyzed; Photrex grade 99.5% pure) was obtained from J.

Simulation of microbial transport and carbon tetrachloride biodegradation in intermittently‐fed aquifer columns

“…[9] Cometabolic degradation of carbon tetrachloride by strain KC proceeds under denitrifying conditions without producing chloroform. In batch biodegradation experiments with 14-C labeled carbon tetrachloride, 40 -50% of the radioactivity was recovered as carbon dioxide, $5% was recovered as formate, and the balance was recovered as unidentified nonvolatile dechlorinated by-products [Criddle et al, 1990a;Dybas et al, 1995]. On the basis of a careful evaluation of known processes, we decided to incorporate the following processes into our model:…”

“…Although indigenous microorganisms may degrade CT, a common by-product is chloroform (CF), which may be more persistent than CT [Criddle et al, 1990a;Semprini and McCarty, 1992]. While CF concentrations can be controlled by manipulation of redox conditions [Criddle et al, 1990b] and nitrate concentrations [Semprini et al, 1990], this may be difficult to achieve under field conditions when in situ remediation is desired [Criddle et al, 1990a;Dybas et al, 1998]. An alternative is to control the reaction pathways through the addition of organisms (bioaugmentation).…”

A three‐dimensional model of microbial transport and biodegradation at the Schoolcraft, Michigan, site

“…The numerical model used in this research simulates the key processes involved in CT biodegradation by the introduced microbe Pseudomonas stutzeri strain KC. This microbe, which was isolated from groundwater in Seal Beach, California [Criddle et al, 1990], transforms CT to carbon dioxide and harmless end products under anaerobic and iron limiting conditions [Tatara et al, 1993, Dybas et al, 1995. Under such conditions, strain KC can use nitrate as an electron acceptor and acetate as an electron donor for growth and produces pyridine-2,6-bis(thiocarboxylate) or PDTC [Lee et al, 1999], which then mediates the CT dechlorination reaction.…”

A Pseudomonas stutzeri gene cluster encoding the biosynthesis of the CCl4‐dechlorination agent pyridine‐2,6‐bis(thiocarboxylic acid)

“…Biological destruction of CCl 4 has been studied to identify transformation activities that may offer economical and effective remediation of this problem. CCl 4 dehalogenation activity has been identified among strictly anaerobic and facultative bacteria (Egli et al, 1987;1988;Galli and McCarty, 1989;Criddle et al, 1990;Mikesell and Boyd, 1990;Picardal et al, 1995). Our initial efforts were directed towards denitrification-linked CCl 4 dechlorination, not only because of the versatility of facultative bacteria but also because this was part of a larger effort aimed at remediation of a nitrate and CCl 4 contamination plume (Illman, 1993).…”