BERKELEY, Calif. — A decade ago, a group of biologists, venture capitalists and computer whizzes gathered under the name “clean tech.” They hoped to overturn polluting industries with microorganisms cheerily excreting industrial chemicals through the miracle of reprogramming nature’s genetic code.

The idea lost billions of dollars. Genes may indeed be programmable code, akin to computer software, but it turned out nature was more complex than first believed.

Now, with less fanfare, a few clean tech companies are aiming for a comeback. And the big idea has not changed much: Create cheap, safe and natural materials for fuel, cosmetics and other goods, much the way yeast ferments sugars into alcohol.

This time around, they believe they have better tools for editing genetic codes, measuring results and automating how chemicals are produced at a large scale. They have also set their sights lower, for now targeting just a few chemicals, not remaking how the world powers cars.