Overview of known organohalide-respiring bacteria-phylogenetic diversity and environmental distribution

To date, organohalide respiration (OHR) has been restricted to the bacterial domain of life. Known organohalide-respiring bacteria (OHRB) are spread among several phyla comprising both Gram-positive and Gram-negative bacteria. As a unique trait, OHRB benefit from reductive dehalogenase enzymes enabling them to use different organohalides as terminal electron acceptors and occupy a wide range of terrestrial and aquatic environments. This chapter comprises three sections: First, we give an overview of phylogeny of known OHRB and briefly discuss physiological and genetic characteristics of each group. Second, the environmental distribution of OHRB is presented. Owing to the application of molecular diagnostic approaches, OHRB are being increasingly detected not only from organohalide-contaminated groundwaters and sediments but also from pristine environments, including deep oceanic sediments and soils that are ample sources of naturally occurring organohalides. Finally, we highlight important factors that impact the ecology of OHRB and their interaction with other microbial guilds.