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 To
understand the signalling communication between the bacterium Vibrio
fischeri and its symbiotic host, the Hawaiian squid Euprymna scolopes,
we have begun to identify bacterial genes that play an essential role in
bacterial colonization of the symbiotic light organ. Normally, E. scolopes
juveniles, upon hatching, will become rapidly colonized by V. fischeri
cells present in the seawater. Concomitant with colonization is an induction
of bacterial bioluminescence, which rapidly reaches a high level (Fig.
1). This high level of bioluminescence ultimately parallels the level of
colonization.
We predicted that V. fischeri mutants defective in their ability to enter or achieve high cell densities in the light organ would also display apparent defects in their symbiotic luminescence levels. Vice versa, an apparent defect in symbiotic luminescence levels may be due to an inability of the mutant V. fischeri cells to colonize. Using these predictions, we have screened a library of mutant V. fischeri cells for defects in their levels of bioluminescence (Fig. 2). This approach has yielded two mutants that have significant colonization defects: One, KV712, exhibits a ~100- to 1000-fold decrease in colonization levels, while the other, KV733, exhibits a 10-fold reduction relative to the wild-type strain (Fig. 3).
Characterization of KV712 revealed that the strain is defective for a protein with sequence similarity to the sensor kinase component of two-component regulators (Fig. 4). In bacteria, the sensor kinase is responsible for recognizing an external signal and relaying that information to the second component, a "response regulator" protein. The signalled response regulator typically binds to DNA and modulates gene expression (increasing or decreasing the transcription of a particular gene).
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| Contact Person: Dr. Karen Visick | Last Reviewed: Feb 10, 2009
Created: Sept 18, 1998 |
©1995-2009
Loyola University Chicago Stritch School of Medicine.
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The
sequence similarity between the gene defective in KV712, now termed rscS
(regulator of symbiotic colonization) and sensory
kinases allows us to make predictions about the role of RscS in the symbiosis.
We hypothesize (Fig. 5) that a putative periplasmic loop of RscS recognizes
a signal from the squid, transmits the information to a putative response
regulator protein, "RscR", that then functions to up-regulate transcription
of genes that are required for the symbiotic phase of the V. fischeri
life cycle. Our ongoing work seeks to provide support for this model and
identify the missing components.