Researchers from Georgia Institute of Technology have isolated a novel bacterium, which can destroy harmful chlorinated compounds in polluted environments, leaving behind environmentally benign end products. This naturally occurring bacterium, known as Dehalococcoides strain BAV1, may be helpful to clean up ground water and subsurface environments contaminated with the common solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). These toxic compounds are primarily used in dry cleaning operations and degreasing of metal components. The researchers used the bacterium Dehalococcoides strainBAV1 in a pilot study at such site, where tetrachloroethene (PCE) penetrated the water table and contaminated drinking water wells. In the test plots at the site, researchers compared a non-treated control plot with other plots applying two bioremediation techniques using the bacterium Dehalococcoides BAV1, which was already present at this site in low numbers. One technique, called biostimulation, added lactate and nutrients to the contaminated plot. The researchers injected a mixed culture containing high numbers of BAV1 along with nutrients using the another technique called bioaugmentation, at the second contaminated plot. This technique resulted in complete dechlorination of PCE to ethene within six weeks. Biostimulation, on the other hand, worked but took more time to accomplish detoxification.

This novel research has been reported in the journal “Nature”, which reveals that the growth of BAV1 depends strictly on the reduction of these chlorinated compounds to ethene and the presence of hydrogen as an electron donor. The finding opens the door for designing more efficient and successful bioremediation strategies for thousands of contaminated sites that remain threats, despite years of expensive clean-up work.

Cleaning up a site contaminated with heavy metals usually requires extensive bulldozing to remove the affected soil. This is very costly, unfriendly to the environment and requires a disposal site for the contaminated soil. But plants that can take up and store heavy metals could be a practical and relatively cost effective way for cleaning contaminated sites. In this direction, researchers at the University of California, San Diego have demonstrated that a chemical that permits plants to detoxify heavy metals can be transported from the roots to stems and leaves. This study can be a key step to clean the soil, which is contaminated with toxic metals, such as lead, arsenic and cadmium. The researchers have found that the chemical – phytochelatin, produced by an enzyme, functions in the root to leaf of a plant to transport and store these toxic metals. Although phytochelatins are found in most of the plants, the researchers used Arabidopsis, which is a relative of the mustard plant. The researchers took a mutant variety of Arabidopsis, which lacks the genes to synthesize phytochelatins, and genetically modified the mutant plants, targeting the gene for the enzyme that synthesizes phytochelatins in the roots of the plant. In an interesting study, the phytochelatins, while only synthesized in the roots, were found in the leaves and stems as well. In addition, when the researchers exposed the roots of the genetically modified plants to cadmium, arsenate and mercury, the plants had restored resistance to these heavy metals. Furthermore, expression of the gene only in roots increased the accumulation of cadmium in leaves. This suggests that engineering plants with the gene to synthesize phytochelatins in roots could make plants contribute to bioremediation. The researchers also demonstrated that the phytochelatins can be transported from roots to shoots and have a key role in preventing over-accumulation of cadmium in roots and enhancing long distance cadmium transport to leaves.

Arsenic occurs naturally in rocks and in this form it is harmless. But when it is exposed to air and water, it becomes soluble and toxic to plants, animals and humans. This is a serious concern for mines. Mining and boring rock for drinking wells can expose the rock-bound arsenic to air and water, and turn it into two toxic forms: arsenate and arsenite. In this context, scientists at La Trobe University, Australia have succeeded in isolating a bacterium, i.e. NT-26, which eats arsenite and excretes arsenate. They have found the enzyme directly responsible for converting arsennite to arsenate. The scientists are working to identify the same enzyme in other microbes. They are also exploring other proteins and genes involved in eating arsenite. The research is being carried out considering the fact that arsenate is easy and safe to get rid of. But arsenite is not, though it can be removed by the use of arsenite-eating bacteria on a mass scale.

Scientists at the University of California have isolated microorganisms capable of degrading endosulfan, a chlorinated insecticide widely used all over the world. Out of 10 microorganisms isolated and screened for their degradable capability for endosulfan, the strains isolated, namely Fusarium ventricosum and Pandoraea sp., were found to degrade about 90% and 83% of 100 ppm endosulfan respectively, in 15 days using the pesticide as a carbon and energy source. Other bacterial strains that were isolated using endosulfan as a sulfur source could degrade about 70% endosulfan. The results of the study suggest that these strains are a valuable source of endosulfan-degrading enzymes and may be used for the detoxification of endosulfan in contaminated soils, waste dumps and water bodies, as well as agricultural dealership sites, wastewater from recycling plants and unused or expired stockpiles of endosulfan.

Microbiologists at Cornell University have discovered microbes that degrade naphthalene in coal tar contamination. The naphthalene-eating bacterium, Polaromonas naphthalenivorans srain CJ 2 was discovered in a 40-year-old municipal gasworks coal tar disposal site, near the west bank of the Hudson river in U.S. The researchers have doubt that the strain CJ 2 alone won’t solve the coal tar problem because naphthalene is only one of the many organic chemicals involved. That is why they are looking for other microorganisms – perhaps with similar gene sequences – that might be biodegrading other toxins. The researchers are also trying to degrade the other carcinogenic elements in coal tar, known as polycyclic aromatic hydrocarbons.