VT College of Science presents Breakthrough - A Student Research Magazine Vol. 1 No. 1 | Page 5

BREAKTHROUGH MAGAZINE | 2014

“My senior graduate students, Revathy and Alison, have worked
well together as a team; they have complementary skill sets. In

Comments from

Dr. Ann Stevens

collaboration with Dr. Roderick Jensen, they have pioneered RNA-Seq methods to study bacterial transcriptomes on the VT campus. Through their efforts, we now have a greater understanding of the genes
directly controlled through quorum sensing in both Vibrio parahaemolyticus and Pantoea stewartii. Although this is basic research, the ultimate goal would be to have practical disease intervention strategies
evolve from this work.
In my research group, the graduate students take a primary ownership role in their projects. We
work together to design experiments, but they are the ones that ultimately carry them through. Then
we again work together to prepare the results for presentation and publication, such as this COS article. By the time a Ph.D. student is
ready to graduate, it is my goal that they have become an independent scientist ready to take on new challenges.”

Quorum Sensing:
The Bacterial Social Network
Alison Kernell Burke, Revathy Ramachandran, & Ann M. Stevens
Bacteria are unicellular organisms that are found in every possible environmental niche on the planet, including on and within
humans. Even though they are single-celled, they have developed a means to communicate with one another, thus achieving multi-cellular cooperation within a population, similar to a social network. The coordinated expression of certain bacterial genes is known as
quorum sensing. The quorum-sensing mechanism is controlled through the production of small signaling molecules, historically called
autoinducers, which allow the bacteria to sense their population in an environment. Enzymes in the bacteria produce the autoinducers
and the concentration of an autoinducer can be used as a measure of the density of cells in the medium (Figure 1).
Within the bacteria are key master regulatory proteins whose activity is either directly or indirectly controlled by the
autoinducer concentration. Most Gram-negative proteobacteria use acylated homoserine lactones (AHLs) as their autoinducer signals,
employing slight modifications to the structure to imprint their personal signature, while Gram-positive bacterium preferentially utilize
unique peptide autoinducer signals. In some organisms, complex QS systems have evolved that possess more than one signal and
regulatory protein to respond to those signals. Some specific well-studied examples of regulation using quorum sensing are the control
of bioluminescence in the symbiotic marine bacterium Vibrio fischeri, Ti plasmid transfer in the plant pathogen Agrobacterium tumefaciens, root nodulation by the plant symbiont Sinorhizobium meliloti, and virulence in the opportunistic human pathogen Pseudomonas
aeruginosa. There is great merit in studying these quorum-sensing systems because it aids in understanding when and how bacteria can
trigger disease, allowing the possibility of developing therapeutic intervention strategies. Since not all bacteria use quorum sensing to ()I