The phylumChloroflexicontains several isolated bacteria that have been found to respire a diverse array of halogenated anthropogenic chemicals. The distribution and role of theseChloroflexiin uncontaminated terrestrial environments, where abundant natural organohalogens could function as potential electron acceptors, have not been studied. Soil samples (116 total, including 6 sectioned cores) from a range of uncontaminated sites were analyzed for the number ofDehalococcoides-likeChloroflexi16S rRNA genes present.Dehalococcoides-likeChloroflexipopulations were detected in all but 13 samples. The concentrations of organochlorine ([organochlorine]), inorganic chloride, and total organic carbon (TOC) were obtained for 67 soil core sections. The number ofDehalococcoides-likeChloroflexi16S rRNA genes positively correlated with [organochlorine]/TOC while the number ofBacteria16S rRNA genes did not.Dehalococcoides-likeChloroflexiwere also observed to increase in number with a concomitant accumulation of chloride when cultured with an enzymatically produced mixture of organochlorines. This research provides evidence that organohalide-respiringChloroflexiare widely distributed as part of uncontaminated terrestrial ecosystems, they are correlated with the fraction of TOC present as organochlorines, and they increase in abundance while dechlorinating organochlorines. These findings suggest that organohalide-respiringChlorofleximay play an integral role in the biogeochemical chlorine cycle.

Bioremediation is the use of microorganisms for the degradation or removal of contaminants. Most bioremediation research has focused on processes performed by the domainBacteria; however,Archaeaare known to play important roles in many situations. In extreme conditions, such as halophilic or acidophilic environments,Archaeaare well suited for bioremediation. In other conditions,Archaeacollaboratively work alongsideBacteriaduring biodegradation. In this review, the various roles thatArchaeahave in bioremediation is covered, including halophilic hydrocarbon degradation, acidophilic hydrocarbon degradation, hydrocarbon degradation in nonextreme environments such as soils and oceans, metal remediation, acid mine drainage, and dehalogenation. Research needs are addressed in these areas. Beyond bioremediation, these processes are important for wastewater treatment (particularly industrial wastewater treatment) and help in the understanding of the natural microbial ecology of severalArchaeagenera.

Oil and gas production wells generate large volumes of water mixed with hydrocarbons (dispersed and dissolved), salts (ions), and solids. This ‘produced water’ (PW) is a waste stream that must be disposed of appropriately. The presence of toxic hydrocarbons and ions in PW makes it unsuitable for surface discharge or disposal in groundwater resources. Thus, PW is often injected into deep geological formations as a disposal method. However, the supply of global water sources is diminishing, and the demand for water in industrial, domestic, and agricultural use in water-stressed regions makes PW a potentially attractive resource. PW also contains valuable elements like lithium and rare earth elements, which are increasing in global demand. This review article provides an overview of constituents present in PW, current technologies available to remove and recover valuable elements, and a case study highlighting the costs and economic benefits of recovering these valuable elements. PW contains a promising source of valuable elements. Developing technologies, such as ceramic membranes with selective sorption chemistry could make elemental recovery economically feasible and turn PW from a waste stream into a multi-faceted resource.

A large number of chlorinated contaminants are found in wastewater, originating from domestic and industrial sources and from runoff captured by sewers. The presence of some of these contaminants, such as the pharmaceutical diclofenac, has recently been documented, whereas the presence of other contaminants, such as polychlorinated biphenyls, has been known for many years. This mini-review discusses the current state of knowledge regarding the degradation and outflow of chlorinated contaminants from municipal wastewater treatment plants (WWTPs) and the known physiologies of bacteria capable of degrading these contaminants, and summarizes current knowledge gaps as a way to focus future research efforts.