I usually tend to downplay worries about research in genetics, but I was quite concerned after reading “Expanding the genetic code” (SN: 4/2/05, p. 222). The researchers surely have plans to keep whatever they create contained. But adding a fifth base to the DNA of bacteria with a genetic mutation rate 10,000 times that of normal bacteria seems unnecessarily dangerous. I guess my concerns were primed by this article, which discusses an “alien green alga that’s currently wreaking havoc in the Mediterranean Sea.”

Andy Olesin
Princeton, Mass.

The concerns connect in your articles about man-made seaweed and scientists creating a fifth base for DNA in bacteria. These human-modified species get loose, and bad things happen.

Gil Stevens
Fairview, Texas

It’s unlikely that a bacterium would survive with such a high mutation rate. What’s more, should such modified organisms make their way into the environment, they would need a constant supply of 3-fluorobenzene, and there’s none of that chemical in the environment. Furthermore, the seaweed wasn’t genetically modified. —A. Goho