The paper was authored by an international team* of collaborators including Trevor Swartz, lead author who was a former postdoctoral and visiting investigator at Carnegie’s Department of Plant Biology at the time of the study, and Winslow Briggs and Tong-Seung Tseng currently at the department. The research appears in the August 24 issue of the journal Science. It is the first detailed study into the function of plant-like light-sensing molecules in bacteria.
“The central message is that many bacteria have signaling proteins that contain the same light-absorbing domain as those found in the higher plants,” Briggs explains. “One of these is a vicious pathogen called Brucella. A species of Brucella is a serious pathogen of cattle that causes abortion of calves, and another species is a nasty pathogen of humans.”
The bacterial sensors are closely related to phototropins—the light receptor molecules that cause a plant to grow toward a light source. They share a protein sequence called a LOV (pronounced “love”) domain, so named because it can detect light, oxygen, and/or voltage. Briggs and his colleagues were the first to discover and describe plant LOV domains in 1998.
LOV-domain proteins have been found in more than 100 different bacteria. For the purposes of this study, the researchers narrowed the field to a handful of candidates with well-known LOV sequences that closely resemble those in plants. They eventually settled on four species: Brucella melitensis, Brucella abortus, Erythrobacter litoralis and Pseudomonas syringae.
In the case of B. abortus, and possibly others, the presence of a LOV domain is more than mere coincidence. When the researchers disabled the LOV-domain protein gene in this species, its virulence—measured as the ability to reproduce efficiently enough to cause disease—dropped to less than 10% of normal, “wild-type” bacteria.
In a simple experiment involving two layers of light-blocking aluminum foil, they achieved a similar drop in virulence, demonstrating that B. abortus depends on sunlight to do its dirty work.
“Brucella has been extensively studied for years because of its threat to livestock and the effect it has on our food supply—one of the key reasons we pasteurize milk is to prevent infection by Brucella,” explained Swartz. “But no one has previously demonstrated any type of light response in Brucella’s lifecycle. This is an exciting result that could possibly provide for a novel therapeutic avenue to treat and prevent infection.”
“People studying non-photosynthetic bacteria, whether the bugs are pathogenic or not, pay no attention to light conditions and are completely unaware that light might play some essential role in their physiology,” Briggs added.
When it is in the dark, a LOV domain uses weak chemical bonds to hold onto a small molecular group known as a chromophore. When it absorbs light, however, the LOV domain temporarily tightens its grip on the chromophore by forming a more stable bond. This reaction is essentially a biochemical switch, and when the light source is blocked or removed, the LOV domain relaxes its grip on the chromophore once again. Activated LOV domains can switch on yet another signaling molecule, known as a kinase, forming a coupled biochemical pathway referred to as a "two-component system."
The function of LOV proteins is fairly well documented in plants. Although researchers had previously documented LOV proteins in bacteria, Briggs, Tseng, Swartz, and their colleagues are the first to examine their function in detail. They found that bacterial LOV domains activate a common signaling pathway that begins with a specific type of kinase known as histidine kinase.
“Bacteria have a large collection of these so-called histidine kinases that are activated by nutrients such as sugar and amino acids, or toxic substances,” Briggs said. “Our work is the first ever to demonstrate a light-activated histidine kinase in a bacterium and demonstrate that it plays an essential role in bacterial virulence.”
*In addition to Briggs, Tseng, and Swartz, co-authors on the paper are: Marcus A. Frederickson and Roberto A. Bogomolni of the University of California, Santa Cruz; Gastón Paris and Fernando A. Goldbaum of the Fundacion Instituto Leloir, CONICET, Buenos Aires, Argentina; Diego J. Comerci and Rodolfo A. Ugalde of the Instituto de Investigaciones Biotecnológicas, Universidad Nacional de San Martín, CONICET, San Martín, Argentina; Gireesh Rajashekara of the University of Wisconsin and Ohio State University; Jung-Gun Kim and Mary Beth Mudgett of Stanford University; and Gary A. Splitter of the University of Wisconsin.
**Swartz initiated the study while a research faculty member at the University of California, Santa Cruz; he is currently at Genentech, Inc.
This research was funded by the National Science Foundation, the National Institutes of Health, the US Department of Agriculture, the Howard Hughes Medical Institute, the Binational Agricultural Research and Development Fund, and the Agencia Nacional de Promoción Científica y Tecnológica (Argentina).
The Carnegie Institution of Washington (www.carnegieinstitution.org), a private nonprofit organization, has been a pioneering force in basic scientific research since 1902. It has six research departments: the Geophysical Laboratory and the Department of Terrestrial Magnetism, both located in Washington, D.C.; The Observatories, in Pasadena, California, and Chile; the Department of Plant Biology and the Department of Global Ecology, in Stanford, California; and the Department of Embryology, in Baltimore, Maryland.
Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH
Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences