VT College of Science presents Breakthrough - A Student Research Magazine Vol. 1 No. 1 | Page 6

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BREAKTHROUGH MAGAZINE | 2014

thereby affecting yield. The production of Stewartan is controlled by quorum sensing via the key master regulatory protein, EsaR, which
prevents production of Stewartan at low cell density. At high cell-density, such as in the xylem, EsaR is bound by the AHL signal causing
it to become inactive, thus allowing for the production of Stewartan. Interestingly, it’s not just the production of Stewartan which
causes virulence, but the timing of its production at the correct stage of infection which leads to successfully establishing disease. Apart
from repressing expression of Stewartan, EsaR can also enhance the
production of certain proteins. Recent work in our laboratory has
used proteome (all proteins expressed in a cell at a given time) and
transcriptome (all RNAs/genes expressed at a give time) approaches
to putatively identify more than ~200 genes under direct and indirect
EsaR regulation. Characterization of the genes regulated by EsaR/
quorum sensing will lead to the discovery of additional factors crucial
in plant pathogenesis. Separately, we are also studying the structure
and function of the EsaR protein itself in collaboration with Florian
Schubot (Virginia Tech) as a better understanding of the regulatory
mechanism whereby the AHL controls its activity. This will provide
valuable insights that may guide drug discovery for the broader LuxR
family of quorum-sensing regulators in the future.

Like Ramachandran, most of Kernell
Burke’s research takes place in the lab.

Vibrio parahaemolyticus is an emerging pathogen that causes gastroenteritis when infected raw or undercooked shellfish
is consumed. It is commonly found in Japan and the Chesapeake Bay Region of Virginia, and as the temperature of the oceans have
increased,V. parahaemolyticus contamination has expanded farther south and north of the equator leading to global outbreaks of
disease. V. parahaemolyticus has a complex quorum-sensing pathway with three proteins producing three different autoinducers that
Low Cell Density

High Cell Density

help the organism sense itself, other Vibrios, and a universal signal
to sense both Gram-positive and Gram-negative organisms that
are in close proximity to V. parahaemolyticus, respectively. The
amount of autoinducer signal controls a signal transduction
cascade, which includes a series of phosphorylated proteins and
small RNA regulators that control the activity of the key master
regulator OpaR indirectly. Similar to our studies in P. stewartii, we
have used a transcriptome (RNA-Seq) approach to determine the

= Autoinducer
= Bacteria Cell

downstream targets of OpaR. Together with collaborators Linda
McCarter (University of Iowa) and Roderick Jensen (Virginia Tech)
have identified over 900 genes that are activated or repressed by
OpaR. Ultimately, we are interested in using a systems biology

Figure 1: Cartoon drawing showing low amounts of autoin-

approach to develop the hierarchy and regulatory feedbacks con-

ducer (blue stars) at a low cell density of bacteria (yellow

trolling gene expression downstream of OpaR. This regulatory

circles) and large amounts of autoinducer at high cell density.

network controls

The change in autoinducer concentrations allow for a change

the cell surface

in coordinated gene expression.

motility, biofilm
formation and

Further Reading:
Fralin Life Science Institute Article:

virulence of V. parahaemolyticus. A better understanding of how V. parahaemolyticus has
evolved both to survive in its environmental reservoir and to cause human disease may
lead to intervention strategies.
Basic studies of QS systems such as those taking place in our laboratory allows

“Graduate student hopes
quorum sensing research
will have broad impact”

us to understand the language and sociobiology of bacteria. This work is necessary
to ultimately give researchers the ability to manipulate bacterial biological processes to benefit society, such as preventing disease or
enhancing beneficial symbioses.