On solid surfaces, many pathogenic bacteria and fungi are able to grow in thin sheets called biofilms. These films can readily form a slick on artificial hips, contact lenses and in catheters. And as such, they can be very dangerous: antibiotics cannot reach the cells inside them very well to kill them off. Each year, thousands of deaths result from these infections.

Baker's yeast (Saccharomyces cerevisiae), a harmless fungus used to make bread and beer, has now given researchers from the Whitehead Institute for Biomedical Research a molecular clue about how biofilms form. In today's Science, they report that yeast cells lacking a gene called FLO11 no longer stick to plastic. This adherence is the first step bacteria must take to form biofilms.

The gene encodes a cell surface protein and has relatives in a biofilm-making pathogenic yeast of the Candida type. Moreover, the crippled baker's yeast cells are unable to form dense, flowerlike "mats"which are similar to biofilmson the surface of petri dishes that contain a special growth medium (see image).

FLO11 is only one gene that fungi seem to need for a biofilm. But because all the genes of baker's yeast are known, researchers can hopefully now use it as a model to find the other molecules involved. If the plan works out, drugs against these molecules could someday prevent biofilms from forming in the human body.