In this review, the strategies being employed to exploit the inherent durability of biofilms and the diverse nutrient cycling of the microbiome for bioremediation are explored. Focus will be given to halogenated compounds, hydrocarbons, pharmaceuticals, and personal care products as well as some heavy metals and toxic minerals, as these groups represent the majority of priority pollutants. For decades, industrial processes have been creating waste all around the world, resulting in contaminated sediments and subsequent, far-reaching dispersal into aquatic environments. As persistent pollutants have accumulated and are still being created and disposed, the incentive to find suitable and more efficient solutions to effectively detoxify the environment is even greater. Indigenous bacterial communities are capable of metabolizing persistent organic pollutants and oxidizing heavy metal contaminants. However, their low abundance and activity in the environment, difficulties accessing the contaminant or nutrient limitations in the environment all prevent the processes from occurring as quickly as desired and thus reaching the proposed clean-up goals. Biofilm communities provide among other things a beneficial structure, possibility for nutrient, and genetic exchange to participating microorganisms as well as protection from the surrounding environment concerning for instance predation and chemical and shear stresses. Biofilms can also be utilized in other ways as biomarkers for monitoring of stream water quality from for instance mine drainage. The durability and structure of biofilms together with the diverse array of structural and metabolic characteristics make these communities attractive actors in biofilm-mediated remediation solutions and ecosystem monitoring.

Anaerobic microbial dechlorination is an important step in the detoxification and elimination of polychlorinated biphenyls (PCBs), but a microorganism capable of coupling its growth to PCB dechlorination has not been isolated. Here we describe the isolation from sediment of an ultramicrobacterium, strain DF-1, which is capable of dechlorinating PCBs containing double-flanked chlorines added as single congeners or as Aroclor 1260 in contaminated soil. The isolate requires Desulfovibrio spp. in coculture or cell extract for growth on hydrogen and PCB in mineral medium. This is the first microorganism in pure culture demonstrated to grow by dehalorespiration with PCBs and the first isolate shown to dechlorinate weathered commercial mixtures of PCBs in historically contaminated sediments. The ability of this isolate to grow on PCBs in contaminated sediments represents a significant breakthrough for the development of in situ treatment strategies for this class of persistent organic pollutants.Polychlorinated biphenyls (PCBs) were manufactured between 1930 and 1978, and their widespread use in high-temperature electrical coolants, hydraulic fluids, paints, carbonless paper, and as dedusting agents has resulted in their global distribution in even the most remote regions of the planet and throughout the food chain. The 2005 Priority List of Hazardous Substances (http: //www.atsdr.cdc.gov/cercla/) published by the U.S. Agency for Toxic Substances and Disease Registry ranks PCBs fifth out of 275 substances. Ranking on this list is a combined metric based on the compound's prevalence at facilities within the United States, known or suspected toxicity, and potential for human exposure. With the discovery of Desulfomonile tiedjei strain DCB1 (24) in 1984, the door was opened for the study of bacteria that can reductively dechlorinate halogenated organic compounds that were manufactured for a wide range of applications throughout the 20th century. Subsequently, it was discovered that such bacteria can couple their growth to reductive dehalogenation in a process referred to as dehalorespiration (15) or halorespiration (15,22). There has been an explosion of discoveries in this field, resulting in the identification of dozens of different species and strains that are capable of dechlorinating compounds ranging from chlorinated ethenes (19) to dioxins (5). Most of the bacteria that reductively dechlorinate toxic halogenated industrial pollutants have turned out to be members of the genus Dehalococcoides. Although several of these microorganisms have been successfully developed for commercially viable bioremediation of soils contaminated with chlorinated solvents, a proven effective treatment for in situ treatment of PCBs does not currently exist. As a result, the only accepted treatments for PCBs are remedial technologies such as dredging and capping, which are expensive, disruptive to the environment, and impractical to implement over large areas and in remote locations.Dehalococcoides ethenogenes strain 195, the first of the...

Strain DF-1 was inoculated into sediments contaminated with weathered Aroclor 1260 to determine whether the augmentation would stimulate the dechlorination of congeners as they occur in the environment, adsorbed to sediment particles and in the presence of an indigenous bacterial population. The 8.9 mol% net decrease in double-flanked chlorines observed after bioaugmentation with DF-1 cannot be calculated directly from the abridged data set in Table 1 on page 2092 that highlighted only some of the changes in absolute amounts. A revised Table 1 (see following page) shows the congener profile that was used to calculate the moles percent decrease catalyzed by DF-1. There are disparities between the tables that resulted from normalization of the data in the published Table 1 to dry mass of soil. The revised moles percent analysis shows that non-double-flanked PCBs 63 and 153 did not decrease with the addition of DF-1, but a slight reduction of non-doubleflanked PCBs 136 and 66/95 was significant, possibly a result of DF-1 dechlorination products serving as "primers" that stimulated the activities by the indigenous population. The relative reduction of double-flanked PCBs 180 and 202 (and coelutants) also appears to be greater. Although we cannot confirm which double-flanked dechlorination reactions were catalyzed exclusively by DF-1, the revised table clearly supports our conclusion that bioaugmentation with DF-1 stimulated reductive dechlorination of weathered Aroclor-contaminated soil.