How to Breathe Bacteria Environmental Toxins

 HU scientists decipher how certain bacteria degrade chlorinated organic compounds

Scientists at the Humboldt University (HU) have discovered how certain bacteria degrade chlorinated organic compounds (Organohalide). For you to solve a decades-old mystery and provide an approach, as can be worked up contaminated soil and water biologically. The results are now published in the online edition of Science magazine.

Chlorine is an aggressive monster. In connection with hydrocarbons occurs since the industrial revolution in the early 20th century chemical far more before than hitherto usual in nature. Chlorinated hydrocarbons are part of lubricants, grease removers in the dry cleaning or pesticides. The problem is that these connections remain long in the environment, because they are very stable. This means they may spread quickly, accumulate in other organisms – including humans – and damage it. The worst twelve compounds, the so-called “Dirty Dozen” was banned in 2001 in the Stockholm UN agreement.

That these toxic Organohalide still be degraded bacteria is due to the breathing these compounds. While humans and animals need the oxygen in the air or in the water to survive, some bacterial species are completely without oxygen and prefer compounds such as nitrate, sulfate or chlorine-containing Organohalide.

Groups of bacteria that may chlorinated hydrocarbons are more frequently found in nature. Scientists are researching for a long time, as these bacteria convert the toxic substances. Now researchers at the Humboldt University have figured out how such bacteria can, thanks to the structure of a particular enzyme breathe chlorine Organohalide.

The working group “Structural Biology and Biochemistry” of the Institute of Biology of the HU studied the biochemical basis of unusual metabolic activities of bacteria, with their focus on the bacterial utilization of carbon monoxide and carbon dioxide as energy and carbon sources and the reduction of environmental pollutants is. Together with the research group “Applied and Environmental Microbiology”, by Prof. Gabriele Diekert of the University of Jena, the HU researchers have investigated the crystal structure of the enzyme clarified that allows the bacterium Sulfurospirillum multivorans allowed to use tetra and trichloroethene as terminal electron acceptors.

The structure of the enzyme is the first of the large class of reductive dehalogenases, allowing different bacteria to specifically implement some hundred different chlorinated and brominated hydrocarbons. In the heart of the enzymes a relative of vitamin B12 acts as a reactive group. Until now it was unclear how the reductive dehalogenases have developed and can be for the sales of certain chlorinated hydrocarbons specific. With its crystal structure, the HU researchers can show how the dehalogenase substrate trichloroethene binds to the cobalt ion of the B12 cofactors and align the implementation, so that an electron transfer to iron-sulfur centers and cobalt ion on trichloroethene cleavage of the chlorine ligands causes. With the structure, the researchers propose a model for the membrane-associated respiration of chlorinated hydrocarbons.

, The numerous bacterial genome sequences that encode most bacteria over a reductive dehalogenase in their genome. Some Dehalococcoides species carry genes for reductive dehalogenases over 30 in its genome. On the basis of crystal structure, and amino acid sequences now approaches can be developed to predict the type of chlorinated hydrocarbons which can detoxify a bacterium. So it should also be possible to further develop the already successful approaches to biological workup Organohalid-contaminated soils and waters.