Cleaning up chemicals with bacteria

A chlorine-eating bacterium has been discovered that could be used to clean up land and water contaminated with decades’ worth of chlorinated organic compounds.

Chlorine-containing pollutants from previous decades of industrial activity have led to serious contamination of groundwater. Polyvinyl chloride (PVC) production and related activities have led to annual underground releases of 137 tonnes of 1,2-dichloroethane in the USA from 1988-1999. 1,2-dichloroethane is a suspected human carcinogen as well as a threat to wildlife and has an environmental half-life of some fifty years.

Stefaan de Wildeman

Stefaan de Wildeman

Until now, there has been no detoxification technology available that could remove this compound from the reducing conditions of groundwater. But, thanks to Belgian researchers who have enlisted a new agent, it might soon be possible to clean up contaminated water without recourse to chemical means.

Stefaan de Wildeman of Ghent University and his colleagues began looking for a bacterium that could metabolise chloroethane rapidly, completely, and reductively. The by-product would be a dechlorinated hydrocarbon and hydrogen chloride. They also hoped that the same microbe might not be averse to digesting other chlorinated alkanes such as 1,2-dichloropropane. Previous researchers had found that certain bacteria could dechlorinate some organochlorine compounds but only with chemical additives present and then only very slowly. The unfortunate by-product of the process was the toxic material vinyl chloride. So bioremediation with these microbes would do more harm than good.

Greenpeace representation of PVC entering environment as waste over the coming decades

Greenpeace representation of PVC entering environment as waste over the coming decades

The Ghent researchers had pinned their hopes on finding a dechlorinating microbe that would be much faster and more controllable and most importantly produce only innocuous by-products. They began to look at soil bacteria found in the air-free conditions of wet soil at a depth of one metre that had been polluted with dichloroethane for some thirty years. It was a struggle to isolate just such a bacterium but with a bit of biological expertise and a little luck the team obtained a growing culture of a dechlorinating bacterium, which was designated strain DCA1.

Accumulating PVC waste

Accumulating PVC waste

The researchers say that strain DCA1 respires the pollutant 1,2-DCA much like animals respire oxygen. Energy is released in the process that allows the organism to live and to reproduce. Physiological, morphological and phylogenetic characterization of DCA1 suggested that it is a new genus of Desulfitobacterium.

The team has offered a full name of Desulfitobacterium dichloroeliminans strain DCA1. As well as defining the species, the team has defined the growth medium required to cultivate what they say is the first nutritionally defined bacterial isolate that completely and rapidly dechlorinates some chlorinated solvents. They say that the growth medium allows them to mass produce the microbe by fermentation.

Further studies have also revealed the specific and stereoselective dehalogenating enzyme present in strain DCA1. Most importantly, from the point of view of bioremediation is that unlike previously known dehalogenating anaerobes, DCA1 does not convert nor produce any unsaturated chlorosubstrates.

Injecting culture solution of strain DCA1 into contaminated groundwater could provide an inexpensive but nevertheless efficient remediation strategy. Its potency has already been demonstrated on groundwater samples in the laboratory while ongoing tests have also showed it to be effective in soil systems under experimental conditions. Degradation is complete and almost no pollutant remains, say the researchers, all within a few days or weeks.

Further reading

ALMA’s cosmic agreement

The European Southern Observatory has given the green light for the world’s most powerful radio observatory. The ESO and the US National Science Foundation (NSF) have signed a joint agreement to construct and operate a millimetre and sub-millimetre wavelength telescope. At these wavelengths, which cross the boundary between the infrared and microwave portions of the electromagnetic spectrum, the key to understanding such processes as planet and star formation, the formation of early galaxies and galaxy clusters, and the formation of organic and other molecules in space, may be found.

The Atacama Large Millimeter Array (ALMA) will encompass sixty-four interconnected 12-metre radio antennae at the uniquely high altitude (5000m) of Chajnantor in the Atacama region of the Chilean Andes. The air here is very dry and so transparent to the crucial wavelengths ALMA will observe. It will be many orders of magnitude the power of any current radio telescope. Such telescopic power will be able to observe much of the energy in the Universe that is present at these low energies. It will see energy from cold cosmic dust and gases in interstellar space and the fading energy of ancient galaxies formed billions of years ago at the edge of the known Universe.

ALMA site

ALMA site

ESO Director General Catherine Cesarsky is highly enthused by the project. This agreement signifies the start of a great project of contemporary astronomy and astrophysics, she says. The ESO will represent its ten member countries and Spain, and work with many laboratories and institutes on the continent. With ALMA we may learn how the earliest galaxies in the Universe really looked, to mention but one of the many eagerly awaited opportunities with this marvellous facility, she adds.

In North America, the NSF also acts for the National Research Council of Canada and executes the project through the National Radio Astronomy Observatory (NRAO) operated by Associated Universities, Inc. (AUI). NSF Director Rita Colwell says that, With this agreement, we usher in a new age of research in astronomy.

A stylised view of ALMA

A stylised view of ALMA

The Republic of Chile also stands to benefit from this astronomical Euro-American alliance as closer ties are wrought between her scientists and the international astronomers. Each of the two partners will foot half of the 650 million Euro/US Dollar bill for the telescope. The joint ALMA Board, established to oversee the project, met for the first time on 24th February.

Another view of ALMA

Another view of ALMA

The President of the ESO Council, Piet van der Kruit suggests that ALMA heralds a breakthrough in sub-millimetre and millimetre astronomy, allowing some of the most penetrating studies of the Universe ever made. It is safe to predict that there will be exciting scientific surprises when ALMA enters operation. He adds that scientists from all over the world will use ALMA. Peer-reviewed proposals will help ensure that scientists get time on the telescope on the scientific merits of their project.

Piet van der Kruit

Piet van der Kruit

The prototype system will be in operation in 2004, while the initial scientific operation of the partially completed array will begin in 2007 and the final construction is destined for completion by 2011.

ALMA prototype

ALMA prototype

Further reading

European Southern Observatory
http://www.eso.org/public/

National Science Foundation
http://www.nsf.gov/

ALMA
http://www.eso.org/sci/facilities/alma/

National Radio Astronomy Observatory (NRAO)
http://www.nrao.edu/

Associated Universities, Inc.
http://www.aui.edu/

Piet van der Kruit
http://www.astro.rug.nl/~vdkruit/

Suggested searches

Radio astronomy

Bringing a sense of order to plastics

US chemists are using liquid crystals as templates to help them synthesise novel plastics that conduct electricity. The technique could be used in the leap from laboratory to mass production of polymer-based components for displays, foil-batteries, and microelectronics devices.

Conducting polymers were first discovered in the 1970s by Alan Heeger, Alan MacDiarmid and Hideki Shirakawa, which won the three a share in the 2000 Nobel Prize for Chemistry. They and technologists around the world were quick to realise that polymers would have many advantages over the conventional semiconductor materials used for electronics components. For instance, they would be operable at lower, more efficient, voltages, they would be easily processable, into devices of almost any shape, and would ultimately be much cheaper to manufacture in bulk because of their ease of processibility.

Liquid crystals

Liquid crystals

Plastic electronics was to be the revolution of the turn of the century and once it was found that many conducting polymers also glowed the possibility of a flat-screen TV that could be rolled up in your pocket based on flexible conducting polymers was the classic image of chemistry in action. But, and there is always a but, the electrical conductivity of polymers has not yet reached the levels needed for the wide range of potential applications. This is due in part to structural disorder – a problem that prevails in plastics.

Now, Samuel Stupp and doctoral candidate James Hulvat at Northwestern University in Evanston (USA) have developed a new technique that forces conducting polymers into an ordered structure, which could overcome this obstacle.

Sam Stupp

Sam Stupp

There are many research teams around the world looking for ways to bring order to polymers. Stupp and Hulvat have concentrated their research on one particular group of conducting polymers, the polythiophenes, which the say are the most industrially important class of conducting polymers. They have used the self-organising power of liquid crystals to provide a template in which these polymers can be synthesised with an underlying order not possible in a free reaction.

Liquid crystal structures

Liquid crystal structures

Liquid crystals are fluid phases in which the individual particles have some degree of order as if they were in a solid crystal, which means they are structured. The US team produced a liquid crystalline gel composed of tiny, mutually parallel, hydrophobic (water repellent) cylindrical units, which are suspended in a hydrophilic (water loving) environment. They dissolve the building blocks for the polymer in this gel.

Liquid crystals showing how order generated

Liquid crystals showing how order generated

The building blocks, monomers, are themselves hydrophobic so they remain exclusively within the hydrophobic cylinders. The polymerisation reaction is kick-started with an electric current and the monomers start to link up to form long polymer chains. In a free solution, such polymer chains would kink and coil forming a conglomeration of random chains, reminiscent of a tangled bowl of spaghetti. However, the template cylinders keep the growing chains on the straight and narrow preventing them from becoming entangled. Once the gel is removed the polymeric material retains its order.

Our very simple new method could help in the production of conducting plastics with improved electronic properties, says Stupp. After the liquid crystals template is washed away, the polymers films remain stuck to the surface, an electrode, on which they are formed. Interestingly, these polymeric films essentially ‘copy’ the liquid crystal texture, revealing birefringent domains that match those of the liquid crystal medium, say the researchers. They suggest that the polymerization takes place within the confined nanoscale environment of the liquid crystals’ hydrophobic cores and produces polymer chains oriented parallel to the direction of the liquid crystal order.

The science and technology of low cost organic electronics could be advanced significantly by utilizing self-assembly processes to pattern and control the nanostructure of conducting polymers, adds Hulvat, this could simplify fabrication and improve efficiency of organic light-emitting diodes (OLEDs), organic field effect transistors and other devices.

Further reading

Angew. Chem. Int. Ed. 2003, 42(7), 778-781
http://www3.interscience.wiley.com/cgi-bin/abstract/103019628/START

DOI: 10.1002/anie.200390206

2000 Nobel Prize for Chemistry
http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/

Samuel Stupp
http://www.matsci.northwestern.edu/faculty/sis.html

Suggested searches

Conducting polymers
Liquid crystals
Polymerisation