Difference between revisions of "Part:BBa K239009"

UCL iGEM 2016: Gold Medal (Characterization of an existing BioBrick)

The deterioration of oral health in the elderly is accompanied by an increased prevalence of caries and periodontal disease, which are risk factors for some systemic diseases and nutrition problems (1). The oral cavity is inhabited by a wide range of interacting communities of metabolically and structurally organized microorganisms which synthesize an extracellular polysaccharide matrix (EPS) enabling them to adhere to the surface of the teeth and assemble in matrix-embedded biofilms. Progressing biofilm accumulation puts the bacteria under increasing metabolic stress, which leads to localized metabolite and acid accumulation and a shift in the dynamic homeostasis towards acid-tolerating species such as Gram-positive Streptococcus mutans (3). A resultant decrease in pH causes tooth demineralization and constitutes a mechanism of dental caries. In our project, we designed a biosynthetic device to serve as an alternative in preventative dental care for the elderly. We decided to target pH and an indicator of deteriorating oral health and use it as an system to regulate the relate of antimicrobial peptide known as mutacin III, is effective against a wide range of Gram-positive bacteria implicated in dental caries, e.g. other strains of Streptococcus mutans and Actinomyces naeslundii, while Gram-negative bacteria are resistant to inhibition (5). An existing BioBrick in the iGEM registry (BBa_K239001), designed to detect misfolding of proteins in the periplasm or shear stress has been further characterised to demonstrate the BioBrick functions as a pH inverter.

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Compared to the control, as pH increases from 3.97 to 6.78, GFP expression gradually increases for E. Coli with BBa_K239009. The maximum GFP expression is observed at 6.78. GFP expression increases from 13,556.25 at pH 3.97 to 35,569 at pH 6.78. Beyond this maximum, there is a sharp decline in GFP expression as the starting LB broth increases in alkalinity, falling to 7,394 at pH 7,394. Conversely, for the control, a sharp increase is observed from pH 5393.5 at 3.97 to 38854.5 at pH 5.08. After this, the general trend is one of increasing fluorescence as pH increases, but the increase is more gradual. From this experiment, we have established that BBa_K239009 (spy promoter) previously used to characterise protein misfolding can be used as a pH-sensitive promoter, as well. Thus, we have improved the function and characterization of an existing BioBrick Part.