Nature Biotechnology pp 1140 - 1145

Researchers have engineered plants with a healthy appetite for sucking up the pollutant arsenic and removing it from the environment. Although arsenic pollution is a serious problem around the world because the metal is both toxic and carcinogenic, cleaning up contaminated sites by physically removing soil is expensive and impractical on the scale that is needed. In the November issue of the journal Nature Biotechnology (published online on October 7), researchers at the University of Georgia describe engineered versions of the small weed thale cress (Arabidopsis thaliana) in which two bacterial enzymes are expressed so that the plant can efficiently pump arsenic from soil and accumulate it in leaves for harvest and processing. The use of plants to extract arsenic has the potential to be a cost-effective way of implementing arsenic cleanup.

Most arsenic in soil and water exists in its oxidized form, arsenate, so Richard Meagher and colleagues expressed the bacterial gene arsenate reductase (ArsC) in the plants’ leaves so that arsenate would be transported aboveground from the plants’ roots and converted to arsenite in their leaves. Expression of the second enzyme, gamma-glutamylcysteine synthetase (gamma-ECS), increased a pool of compounds that can bind and detoxify heavy metals, such as arsenite, trapping the complexes in leaves. The approach enables the plants to accumulate and tolerate increased levels of arsenic.

Nature Biotechnology pp 1118 - 1123

The genome sequence of a bacterium that can remove metal toxins from the environment ultimately promises to facilitate the development of new bioremediation strategies for cleanup of contaminated sites. In the November issue of the journal Nature Biotechnology (published online on October 7), a collaboration of researchers at The Institute for Genomic Research, The Center for Marine Biotechnology, Johns Hopkins University, George Washington University Medical Center, Jet Propulsion Laboratory, the University of Arizona, Tucson, and the Carnegie Institution of Washington report the first genome sequence a metal-ion reducing bacterium--that of Shewanella oneidensis. The authors hope that by studying the genome of this organism, researchers will be able to understand the molecular basis of the microbe’s ability to reduce metal pollutants, thereby expediting its use as a tool to help clean the environment.

Analysis of the sequence of S. oneidensis reveals a large circular chromosome with 4,931 predicted genes and a smaller circle of DNA with 173 genes. The authors identify several genes implicated in a highly complex/branched electron transport chain--the chain of membrane-bound proteins/enzymes that produce energy for the bug and enable the microbe to utilize many different compounds in energy production, including metal ions. As many of these metal ions (e.g., uranium and chromium) are common pollutants, S. oneidensis has the ability to reduce them into forms that are more easily removed from water. Computer analysis indicates that S. oneidensis has 39 c-type cytochromes (a type of enzyme involved in electron transport)--more than any other organism sequenced to date. Further study of the electron transport system will be crucial to understanding the physiological process and regulation of biological metal reduction, and will eventually allow researchers to "custom make" new strains of this bacterium for specific applications, such as cleaning up the toxic run off from copper mines.

Elsewhere in the paper, the researchers also make the first ever identification of a Shewanella lambda-like phage, which may provide a potentially important tool for further genome engineering. Another unique property of S. oneidensis is that it, unlike other metal ion-reducing microbes, can survive in the presence of oxygen. This gives researchers great freedom in storing and transporting the bacterium, and also transfers a tremendous practical advantage to using this bacterium for bioremediation.

Nature Biotechnology pp 1103 - 1110 and pp 1111 - 1117

Two studies by a group of researchers headed by Evan Snyder at Harvard Medical School offer hope that transplanted neural stem cells can stabilize and rescue ailing, dysfunctional brain cells. Previously, transplanted stem cells were seen primarily as "replacement" cells that could supplement, not repair, damaged brain cells. The research offers hope that one day neural stem cell treatments may prove useful for treating patients with debilitating neurodegenerative diseases.

The ability of transplanted neural stem cells to replace dead or dying cells in situations where the brain has suffered acute injury has been described in several reports over the past decade. In the new research reported in the November issue of Nature Biotechnology, Snyder and his colleagues wondered whether the stem cells would be useful in two other cases of brain injury.

In a first paper (Ourednik et al.), they ask whether the stem cells are effective against the slow degeneration of brain function in mice treated with chemicals to mimic the process of aging or Parkinson's disease in people. Surprisingly, the transplanted cells were found to rescue damaged host cells, stimulating them to produce more of the enzymes essential for dopamine activity.

In a second paper (Park et al.), the researchers set out to discover whether the neural stem cells can heal injuries in mice missing large parts of the brain-similar to tissue loss in the human condition of severe cerebral palsy. By themselves, the neural stem cells were unable to rebuild the lost tissue. But their regenerative ability was much improved when they were seeded before transplantation into a biodegradeable scaffold. As the scaffold degraded, the cavity filled with new, vascularized brain tissue, and numerous interconnections formed between the host brain and the transplanted stem cells. In addition, inflammation, and scarring were significantly reduced.