HCNSO Student Theses and Dissertations

Defense Date


Document Type


Degree Name

M.S. Biological Sciences

First Advisor

Jose Victor Lopez

Second Advisor

Robert Phillip Smith

Third Advisor

Patricia L. Blackwelder


Cooperation is a trait that is found at all levels of biological organization. Interestingly, cooperation appears to occur in bacteria that produce small, easily diffusible molecules called autoinducers. To understand why bacteria produce these autoinducers, the scientific community has focused on one predominant theory called quorum sensing. Under this theory, bacteria produce autoinducers so they can sense the density of the population. Once a sufficiently high population density is reached, autoinducers initiate the production of a costly gene product that serves to benefit the population. In contrast, a competing theory called diffusion sensing suggests that autoinducers are used by the individual cells and are not used for cooperation. Here, the production of the autoinducer serves as a mechanism to sense environmental conditions. If the environmental conditions are favorable, a costly gene product is produced. To what extent, and under what conditions, are each of these opposing theories valid remains to be identified. In this thesis, an engineered strain of Escherichia coli was used to identify the conditions under which quorum sensing and diffusing sensing can be observed. It was discovered that, depending upon the frequency at which the spatial distribution of the autoinducer and bacteria was disrupted, the population of engineered bacteria displayed hallmarks of either quorum sensing or diffusion sensing. Specifically, when the spatial distribution was disturbed at high or low frequency, quorum sensing was observed. However, when spatial distribution was disturbed at an intermediate frequency, diffusion sensing was observed. Understanding how these disturbances affect survival in bacteria may result in novel treatments for bacterial infections. In more general applications, it may be exploited in the development of alternative mechanisms for controlling invasive species or aid in species reintroduction.

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