Title: Bacterial cross talk in mixed culture.
Abstract: In this Thesis Quorum sensing is the term used to describe signaling pathways used by bacteria for intra and interspecies communication. Autoinducer 2 (AI2) is one signal molecule known to be involved in quorum sensing that stands out because it appears to be expressed across a wide variety of bacterial species. A genetic switch has been created exploits the AI2 quorum sensing pathway by turning on a target marker gene, green fluorescent protein, in the presence of AI2. The purpose of this investigation was to characterize this genetic switch and to investigate its behavior in mixed culture. Specifically to see if E. coli can respond to AI2 from other E. coli cells. It was found that the switch could be turned on by synthetic AI2 and AI2 being made by other cells growing in mixed culture as well by autoexpression. Quorum Sensing: Bacterial cells communicate via small signaling molecules in a process known as quorum sensing. Winzer et al1 proposed specific criteria that distinguished signal molecules from other bacterial metabolites. First, production of the molecule must occur during a specific growth stage, under specific physiological conditions or environmental stimuli. Second, that the signal molecule accumulates in the supernatant and the cell membrane has a receptor for it. Third, that the signal molecule, above a threshold concentration leads to a coordinated response in the cell population and fourth that the response produced involves something other than breaking down the molecule.1 Quorum sensing regulates many different cellular processes that depend on the cells acting in concert. Some processes that have been studied include biofilm formation, bioluminescence and motility. Gram positive bacteria use secreted peptides while Gram negative bacteria, like Escherichia coli, use small chemical molecules, usually an acetylated homoserine lactone (AHL), as their autoinducers. Quorum sensing acts as a function of cell density giving it potential to be exploited for applications as diverse as recombinant protein synthesis and the discovery of novel antibiotics.
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Keywords: Engineering, Chemical.
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