Light sparks bacterial virulence

The notorious pathogen Brucella abortus, which causes abortions in cows and fevers in humans, uses light to regulate its virulence, according to a new study (Science 2007, 317, 1090). A team led by Roberto A. Bogomolni of the University of California, Santa Cruz, discovered that certain bacteria, including B. abortus, contain light-sensing histidine kinases with an LOV (light, oxygen, or voltage) domain. When the protein is exposed to blue light, a flavin cofactor forms a covalent bond with a cysteine residue in the LOV domain. This reaction triggers a conformational change, which signals to the rest of the protein that a photon has been detected. According to Bogomolni's team, light increases the activity of Brucella's histidine kinase, rendering it more virulent. To boot, the researchers showed that the pathogen is 10 times more virulent after exposure to visible light than Brucella kept in the dark. Furthermore, when the researchers removed the gene that encodes the LOV kinase from the bacteria, they eliminated any light-mediated virulence.