Microbial degradation of tetrachloromethane: mechanisms and perspectives for bioremediation

Abstract

Toxic man-made compounds released into the environment represent potential nutrients for bacteria, and microorganisms growing with such compounds as carbon and energy sources can be used to clean up polluted sites. However, in some instances, microorganisms contribute to contaminant degradation without any apparent benefit for themselves. Such cometabolism plays an important part in bioremediation, but is often difficult to control. Microbial degradation of tetrachloromethane (carbon tetrachloride, CCl(4)), a toxic ozone-depleting organic solvent mainly of anthropogenic origin, is only known to occur by cometabolic reduction under anoxic conditions. Yet no microbial system capable of using CCl(4) as the sole carbon source has been described. Microbial growth based on CCl(4) as a terminal electron acceptor has not been reported, although corresponding degradation pathways would yield sufficient energy. Known modes for the biodegradation of CCl(4) involve several microbial metabolites, mainly metal-bound coenzymes and siderophores, which are produced by facultative or strictly anaerobic bacteria and methanogenic Archaea. Recent reports have demonstrated that CCl(4) dechlorination rates are enhanced by redox-active organic compounds such as humic acids and quinones, which act as shuttles between electron-providing microorganisms and CCl(4) as a strong electron acceptor. The key factors underlying dechlorination of CCl(4), the practical aspects and specific requirements for microorganism-associated degradation of CCl(4) at contaminated sites and perspectives for future developments are discussed.

Bioremediation of Heavy Metals from Soil and Aquatic Environment: An Overview of Principles and Criteria of Fundamental Processes

“…Genetic engineering of Deinococcus radiodurans (radiation resistant bacterium) which naturally reduces Cr (IV) to Cr (III) has been done for complete toluene (fuel hydrocarbon) degradation by cloned genes of tod and xyl operons of Pseudomonas putida [90]. Microbial metabolites like metal bound coenzymes and siderophores mainly involved the degradation pathway [91].…”

Microbial Removal of Atmospheric Carbon Tetrachloride in Bulk Aerobic Soils

“…Abiotic degradation of CCl 4 has been observed in the presence of metal and sulfur-containing compounds (6,19,58), including reductive dechlorination under aerobic conditions (35). Biotic removal of CCl 4 has been documented for a variety of anaerobic bacteria (18,32,34,47,67), with the products of degradation varying depending on the redox conditions and type of bacteria mediating the reaction (5,13,14,46,67). Although sulfate-reducing conditions have been shown to enhance CCl 4 transformation in anaerobic column experiments, in some experiments sulfate reducers themselves did not play a role, as evidenced by a lack of inhibition upon amendment with molybdate (13,14).…”

“…Methane (CH 4 ) (5%) was added to soil samples to stimulate methanotrophy (15). Methanol was added to stimulate methylotrophy (1), and the multicarbon compounds acetate and succinate were added, which would have been available for use by various organisms, including facultative methylotrophs (3); these compounds could also act as electron donors for reductive dehalogenation (28,31,46 …”

Unravelling long-term source removal effects and chlorinated methanes natural attenuation processes by C and Cl stable isotopic patterns at a complex field site

“…Identifying sources and tracing their evolution over time is crucial to set up effective decontamination strategies (Penny et al, 2010;Cappelletti et al, 2012).…”

“…by magnetite) initiates with a reduction and leads, after different steps including hydrolysis, to formate, CO and CO 2 as final products. CT "thiolytic reduction", after an initial reduction, produces CS 2 as final product by thiolytic substitution of dechlorinated intermediates, being mediated either by Fe(II)-sulfides or by bacteria (Field and SierraAlvarez, 2004;Penny et al, 2010;Koenig et al, 2012;He et al, 2015). CT reduction by Pseudomonas stutzeri also produces CO 2 as the final product, with transient accumulation of toxic phosgene and thiophosgene (Lewis and Crawford, 1995).…”