Growth of Dehalococcoides spp. and increased abundance of reductive dehalogenase genes in anaerobic PCB-contaminated sediment microcosms

Polychlorinated biphenyls (PCBs) contaminate 19% of US Superfund sites and represent a serious risk to human and environmental health. One promising strategy to remediate PCB-contaminated sediments utilizes organohalide-respiring bacteria (OHRB) that dechlorinate PCBs.

However, functional genes that act as biomarkers for PCB dechlorination processes (i.e., reductive dehalogenase genes) are poorly understood. Here, we developed anaerobic sediment microcosms that harbor an OHRB community dominated by the genus Dehalococcoides. During the 430-day microcosm incubation, Dehalococcoides 16S rRNA sequences increased two orders of magnitude to 10⁷ copies/g of sediment, and at the same time, PCB118 decreased by as much as 70%. In addition, the OHRB community dechlorinated a range of penta- and tetra-chlorinated PCB congeners including PCBs 66, 70?+?74?+?76, 95, 90?+?101, and PCB110 without exogenous electron donor. We quantified candidate reductive dehalogenase (RDase) genes over a 430-day incubation period and found rd14, a reductive dehalogenase that belongs to Dehalococcoides mccartyi strain CG5, was enriched to 10⁷ copies/g of sediment. At the same time, pcbA5 was enriched to only 10⁵ copies/g of sediment. A survey for additional RDase genes revealed sequences similar to strain CG5’s rd4 and rd8. In addition to demonstrating the PCB dechlorination potential of native microbial communities in contaminated freshwater sediments, our results suggest candidate functional genes with previously unexplored potential could serve as biomarkers of PCB dechlorination processes.

     

Chlorinated fatty acids - Environmental pollutants with intriguing properties

The chlorine bound in chlorinated fatty acids (ClFAs) have been concluded to contribute to a major part of the extractable organically bound chlorine found in fish and other aquatic biota. Despite ClFAs giving rise to toxic effects they appear not to be recognised as “xenobiotic” compounds by the organism. They are readily accumulated via food and incorporated into complex lipids to approximately the same extent as unchlorinated fatty acids and may thus be transferred from prey to predator in the food chain. The ClFAs thus diverge from traditional environmental pollutants, such as PCBs, in several aspects and their fate in the environment can not be predicted by conventional risk assessment methods.     

Forest certification--an instrument to promote sustainable forest management?

Forest certification was introduced in the early 1990s to address concerns of deforestation and forest degradation and to promote the maintenance of biological diversity, especially in the tropics. Initially pushed by environmental groups, it quickly evolved as a potential instrument to promote sustainable forest management (SFM). To date about 124 million ha or 3.2% of the world's forests have been certified by the different certification schemes created over the last decade.Forest certification shares the aim of promoting SFM with another tool, namely criteria and indicators (C&I) for SFM. C&I sets are mainly developed for the national level to describe and monitor status and trends in forests and forest management. They also provide an essential reference basis for forest certification standards, which set performance targets to be applied on a defined area. Progress in developing these two different tools has been significant.After 10 years of implementation, it is evident that the original intention to save tropical biodiversity through certification has largely failed to date. Most of certified areas are in the temperate and boreal zone, with Europe as the most important region. Only around ten per cent is located in tropical countries.The standards used for issuing certificates upon compliance are diverse, both between certification schemes and within one and the same scheme when applied in different regions. However, they are at least equal to legal requirements and often include elements that set actually higher standards.While the quality of actual audits of the standards is of varying quality, there are indications that independent audits are an incentive for improving forest management. As a voluntary market-based tool, forest certification is depending on the ability to cover the costs incurred and thus on often-elusive green consumer sentiment.Regardless of many difficulties, forest certification has been very successful in raising awareness and disseminating knowledge on a holistic SFM concept, embracing economic, environmental and social issues, worldwide. It also provides a tool for a range of other applications than assessment of sustainability, such as e.g. verifying carbon sinks.