Bacteria Genomes - DEHALOCOCCOIDES

Bacteria of the genus Dehalococcoides are extraordinarily specialized for a unique physiological niche, detoxifying compounds that are otherwise persistent for decades.

In the past century, human activities have released large amounts of chlorinated organic compounds into the environment, and these compounds are among the most pervasive groundwater pollutants. Chloro-organics with fewer chlorines can usually be biodegraded by aerobic microorganisms, whereas more highly chlorinated ones can be reductively dechlorinated by organisms using them as electron acceptors for anaerobic respiration. Several microbial groups carry out respiratory reductive dechlorination, but Dehalococcoides seems particularly adapted to for this process.

Chlorinated benzenes, Tetrachloroethene (PCE) and trichloroethene (TCE), are highly persistent pollutants which are ubiquitously distributed in the environment and impose a significant risk for human health. PCE and TCE can be transformed to less chlorinated ethenes in anaerobic cometabolic processes mediated by methanogenic, homoacetogenic, and sulfate-reducing microorganisms. Strain CBDB1 is able to grow with trichlorobenzene (TCB), hydrogen, and acetate, indicating that it conserves energy by using TCB as the terminal electron acceptor in a respiratory process. Recently, it was shown that strain CBDB1 also dechlorinates chlorinated dioxins.

Strain CBDB1 contains a single circular chromosome with 1,395,502 base pairs, encoding 1,458 predicted protein coding sequences. Its apecialiaation can be observed in the genome, which contains less than 1.4 Mb and is among the smallest for free-living prokaryotes.

Strains CBDB1 and 195 have been sequenced. It appears that CBDB1 has an even greater potential as a reductive dechlorinator than strain 195 and, in addition, the comparison of the two genomes with each other provides insights into the evolution of reductive dechlorination in this unusual microbial group.

References:

http://www.nature.com/nbt/journal/vaop/ncurrent/full/nbt1131.html
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=154522