Halogenated organic compounds are released into the environment from natural and anthropogenic sources. Many anthropogenic halogenated chemicals, like chlorinated haloalkenes (7
), benzenes (1
), and dioxins (5
), are of particular concern due to their toxicity to humans and other forms of life. This toxicity is often paired with high recalcitrance to degradation, especially in anaerobic environments, leading to persistent contamination.
Anaerobic environments are frequently characterized by limited availability of electron acceptors. Theoretical calculations have shown that coupling the reduction of many halogenated organic compounds to the oxidation of suitable substrates is a way to harness energy (46
). As determined two decades ago, this source of energy is utilized by the microbial community. The oxidation of available electron donors coupled to the reduction of halogenated organic compounds while energy is conserved is called dehalorespiration (7
). Dehalorespiring strains have been isolated independently from contaminated sites around the world. The two most prominent genera resulting from these isolation efforts are Dehalococcoide
) and Desulfitobacterium
), and various strains of these genera are used as model systems to study dehalorespiration (8
195 is one of the few strains isolated to date which can dechlorinate tetrachloroethene (PCE) to ethene (29
). D. ethenogenes
195 can use only hydrogen as an electron donor and chlorinated compounds as electron acceptors (29
strains are also known to dechlorinate a wide variety of substrates, including halophenolic compounds and chloroalkenes (7
). Although several strains can use PCE or trichloroethene (TCE) as an electron acceptor, no Desulfitobacterium
strain isolated so far completely dechlorinates these compounds to ethene (7
). In contrast to Dehalococcoides
strains can utilize electron acceptors other than chlorinated compounds. Several strains that are capable of deiodination (21
) and reduction of As(V), Fe(III), Se(VI), Mn(IV), and a variety of oxidized sulfur species (37
) have been isolated, although currently little is known about how widespread these capabilities are in this genus.
Since Desulfitobacterium and Dehalococcoides strains are frequently encountered at contaminated sites, these genera have attracted considerable attention for use as bioremediation agents. The use of these strains in real life, however, is hampered by the lack of information about how the dehalogenation process is embedded in the general metabolism of the organisms and the conditions that allow these microorganisms to proliferate in the environment.
Here we report the first complete genomic sequence of the
genus Desulfitobacterium. Desulfitobacterium hafniense
Y51 (formerly Desulfitobacterium
sp. strain Y51) was isolated from a contaminated site in Japan based on its ability to efficiently dechlorinate PCE even at its highest water solubility (48
). The recent publication of the D. ethenogenes
195 genomic sequence (43
) allowed us to compare the two sequences and highlight the similarities and differences between the organisms.