Bacteria Caught Double-Dipping Pigments

Ever-industrious bacteria are using redox-active pigments to control colony morphology in addition to using the compounds in their established role as antibiotics, according to a report in Science (2008, 321, 1203). Researchers have long observed that redox-active pigments such as pyocyanin are produced by a variety of bacteria, including Pseudomonas aeruginosa. But the compounds were initially thought to be just waste products. Researchers then discovered that the pigments were actually chemical weapons that harm the bacteria's competitors by initiating the production of superoxide radicals in the rival species. Biologist Dianne K. Newman of Massachusetts Institute of Technology and colleagues now find that P. aeruginosa also uses pyocyanin for the bacteria's own purposes. Pyocyanin is produced in large quantities when P. aeruginosa is among others of its own kind, and the pigment turns on some 35 genes that enable a wide variety of community-oriented processes in the bacteria. For example, pyocyanin-induced gene expression helps P. aeruginosa achieve a compact colony structure ideal for biofilms compared with the spread-out colonies that P. aeruginosa makes when the pigment's production is blocked.