Genetic Engineers Who Don’t Just Tinker

FORGET genetic engineering. The new idea is synthetic biology, an effort by engineers to rewire the genetic circuitry of living organisms.

The ambitious undertaking includes genetic engineering, the now routine insertion of one or two genes into a bacterium or crop plant. But synthetic biologists aim to rearrange genes on a much wider scale, that of a genome, or an organism’s entire genetic code. Their plans include microbes modified to generate cheap petroleum out of plant waste, and, further down the line, designing whole organisms from scratch.

Synthetic biologists can identify a network of useful genes on their computer screens by downloading the gene sequences filed in DNA data banks. But a DNA molecule containing these various genes and their control elements would be a chain of hundreds of thousands of DNA units in length. Though human cells effortlessly duplicate a genome of three billion units, the longest piece of DNA synthesized so far is just 35,000 units long.

Scientists at the J. Craig Venter Institute in Rockville, Md., hope to take a giant stride in synthetic biology by creating a piece of DNA 580,076 units in length from simple chemicals, chiefly the material that constitutes DNA’s four-letter chemical alphabet. This molecule would be an exact copy of the genome of a small bacterium. Dr. Venter says he then plans to insert it into a bacterial cell. If this man-made genome can take over the cell’s functions, Dr. Venter should be able to claim he has made the first synthetic cell.

Such an achievement could suggest some new plateau has been reached in human control of life and evolution. But Dr. Venter’s synthetic genome will probably be seen to represent a feat of copying evolution’s genetic programming, not of creating new life itself.

microbes modified to generate cheap petroleum out of plant waste

Thanks neverdem.

Abstract Number:1027
by Maria L Ghirardi and Michael Seibert
The hydrogen metabolism of photosynthetic bacteria and cyanobacteria involves the coordinated action of three enzymes: nitrogenase, reversible hydrogenase, and uptake hydrogenase. Green algae, on the other hand, contain only the reversible hydrogenase, which is responsible for both hydrogen production and uptake in this organism. The quantum yield for hydrogenase-catalyzed hydrogen production is much higher than that for nitrogenase. Algal hydrogenases, however, are extremely sensitive to oxygen. For this reason, green algae cannot be utilized commercially for hydrogen production. We have investigated two types of selective pressure to isolate mutants of Chlamydomonas reinhardtii that produce hydrogen in the presence of oxygen. The first is based on competition between hydrogenase and metronidazole for electrons from light-reduced ferredoxin. Since reduction of metronidazole results in the release of toxic products that eventually kill the organism, cells with an active oxygen-tolerant hydrogenase will survive a short treatment with the drug in the light in the presence of oxygen. Using this technique, we have isolated a variant of C. reinhardtii that evolves hydrogen with an I50 for oxygen three times higher than the wild type strain. The second selective pressure depends on growth of algal cells under photoreductive conditions. Algal cells must fix carbon dioxide in the presence of oxygen with reductants derived from hydrogen uptake by the reversible hydrogenase. We will describe in detail both selective pressures, as well as the characteristics of the mutants isolated by application of these selective pressures to a population of mutagenized wild type cells. This work was supported by the U.S. DOE Hydrogen Program.

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