Campbell Biology: Concepts & Connections, Global Edition 8th Edition

Book Preface

In many natural environments, prokaryotes attach to surfaces in highly organized colonies callediofilms. A biofilm may consist of one or several especies of prokaryotes, and it may include protists and fungi as well. Biofilms can form on almost any support, including rocks, soil, organic material (including living tissue), metal, and plastic. You have a biofilm on your teeth—dental plaque is a biofilm that can cause tooth decay. Biofilms can even form without a solid foundation, for ex-ample, on the surface of stagnant water.
Biofilm formation begins when prokaryotes secrete signal-ing molecules that attract nearby cells into a cluster. Once the cluster becomes sufficiently large, the cells produce a gooey coating that glues them to the support and to each other, making the biofilm extremely difficult to dislodge. For exam-ple, if you don’t scrub your shower, you could find a biofilm growing around the drain—running water alone is not strong enough to wash it away. As the biofilm gets larger and more complex, it becomes a “city” of microbes. Communicating by chemical signals, members of the community coordinate the division of labor, defense against invaders, and other activi-ties. Channels in the biofilm allow nutrients to reach cells in the interior and allow wastes to leave, and a variety of envi-ronments develop within it.
Biofilms are common among bacteria that cause disease in humans. For instance, ear infections and urinary tract infections are often the result of biofilm-forming bacteria. Cystic fibrosis patients are vulnerable to pneumonia caused by bacteria that form biofilms in their lungs. Biofilms of harmful bacteria can also form on implanted medical devices such as catheters, replacement joints, or pacemakers. The complex-ity of biofilms makes these infections especially difficult to defeat. Antibiotics may not be able to penetrate beyond the outer layer of cells, leaving much of the community intact. For example, some biofilm bacteria produce an enzyme that breaks down penicillin faster than it can diffuse inward.
Biofilms that form in the environment can be difficult to eradicate, too. A variety of industries spend billions of dollars every year trying to get rid of bio- films that clog and corrode pipes,  gum up filters and drains, and coat  the hulls of ships (Figure 16.5).
Biofilms in water distribution  pipes may survive chlorination,  the most common method of ensuring that drinking water does  not contain any harmful micro organisms. For example, biofilms of Vibrio cholera, the bacterium
that causes cholera, found in water  A biofilmfouling the insides of a pipe pipes were capable of withstanding  levels of chlorine 10 to 20 times higher than the concentrations routinely used to chlorinate drinking water.