Autoinducer 2 (AI-2) molecules produced by bacterial cells are thought to be
involved in controlling a variety of bacterial cellular processes by coordinated gene and
protein expression. Previous work in our laboratory has shown that ground beef contains
compounds that can interfere with AI-2-mediated bioluminescence expression in Vibrio.
harveyi. The underlying hypothesis of this work was that AI-2 molecules affect the
protein expression in Escherichia coli O157:H7 and AI-2 inhibitory molecules negate
the influence of AI-2 molecules. The main objectives of this study were to identify,
characterize, and isolate the factors responsible for inhibition of AI-2 molecules from
ground beef extracts, elucidate the role of LuxS/AI-2 cell signaling system in E. coli
O157:H7 protein expression, and determine if inhibitory factors present in ground beef
extract can negate the influence of AI-2 molecules on the protein expression. Using a
solvent extraction procedure and gas chromatography analysis, AI-2 inhibitory factors
present in ground beef extracts were identified as both medium and long chain fatty
acids. When identified fatty acids were tested at different concentrations for AI-2 inhibition, AI-2 inhibition ranging from 25% to 90% was observed. Both ground beef
extracts and mixture of selected fatty acids also resulted in 2- to 4-fold reduced AI-2
influenced biofilm formation by E. coli K12 cells. Identification of LuxS/AI-2-mediated
protein expression in E. coli O157:H7 was conducted using two dimensional gel
electrophoresis. Protein expression analysis showed that the LuxS/AI-2 system
modulates the expression of proteins involved in different cellular processes such as
carbohydrate and amino acid metabolism, stress response, and formation of flagella and
motility. When AI-2 inhibitory factors were added along with AI-2 molecules, the
expression patterns of three AI-2-influenced proteins (GlmS, SpeE, and NikA) were
changed suggesting that AI-2 inhibitors can negate the influence of AI-2 molecules on
protein expression of selected proteins. Collectively, these results highlight that proteins
associated with different cellular processes in E. coli O157:H7 can be modulated
depending on whether cells are in contact with AI-2 molecules in the presence or
absence of AI-2 inhibitory factors.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2747 |
| Date | 15 May 2009 |
| Creators | Soni, Kamleshkumar A. |
| Contributors | Pillai, Suresh |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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