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IPTG activates the Lac/AraC promoter

A culture of 2ml of E. coli containing a construct with the Lac/AraC promoter in front of YFP variant Venus was grown overnight at 37°C and then transferred to 25 ml of ampicillin LB broth. This culture was then grown at 37°C in a shaking incubator for 2.5 hours so as to ensure that the bacteria were in their exponential growth phase. The culture was then imaged using fluorescent microscopy with the excitation and emission maximums set for yellow/green fluorescence to detect YFP.

A baseline reading (Fig 1) was taken at this point (Tile A), to determine the presence of non-specific promoter activation. 10% 1mM IPTG was then added and the culture returned to the shaking incubator. An aliquot was then imaged after 30min (Tile B), and again after 1 hour (Tile C). All aliquots used in imaging were 100 ul.

As is seen in the baseline image (Tile A), the degree of fluorescent activation is minimal before the addition of IPTG. Tile B shows the fluorescent activation after 30min incubation with IPTG - there is very little visible fluorescent activation. After an hour of incubation (Tile C) there is a marked increase in the degree of fluorescence, thus providing an indication that IPTG has a positive effect on the Lac/Ara-1 promoter, activating gene expression.


Figure 1. Time course fluorescent microscopy of Lacto-detect before and after induction with IPTG

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