Washington ? By modifying a simple microbe, scientists hope to create a form of single-cell life that could lead to new and cleaner energy and perhaps play a role in biological warfare. But there are safety and ethical concerns in this new world of biology, experts say.

A group led by J. Craig Venter, director of a private program that mapped the human genome, has received a $3 million Department of Energy grant to make a new type of bacterium using DNA manufactured in the lab from basic chemicals.

The goal, Venter said, is to build a bacterium that is capable of making hydrogen that could be used for fuel, or to develop a microbe that could absorb and store carbon dioxide, thus removing a surplus of that greenhouse gas from the atmosphere.

Along the way, scientists will learn on a molecular level the minimum genes a cell needs to thrive and reproduce and how to artificially make those and other genes, he said.

“This is true basic science,” Venter said. “Even though we’ve found all those genes in the human genome, we can’t understand the most basic simple cell yet. That is what is driving this.”

Some experts worry that by learning how to artificially create the basic genes essential to life ” even in a fragile, obscure microbe ” scientists may open a new door to biological hazards and, perhaps, put a new weapon into the hands of terrorists.