Part:BBa_K554013:Experience
SoxS HlyB HlyD TolC device
This part was used to [http://2011.igem.org/Team:UNICAMP-EMSE_Brazil/Results#Device_3_testing.2C_Protein_Secretion_System Device 3 testing, Protein Secretion System]
Device 3 testing, Protein Secretion System
The assembled devices related to secretion system (Hemolysin secretion system under control of SoxS – SoxS-HlyB-HlyD-TolC) was tested under laboratory conditions using GFP as reporter.
Methods
To access GFP secretion, competent E. coli DH5α strain cells were transformed simultaneously with a pSB1C3 vector (Chloramphenicol resistant) carrying both the sensor (Strong_Constitutive_promoter + RBS + SoxR + Terminator) and the effector (SoxS_promoter + RBS + GFP + HlyA + Terminator), and pSB1AK3 (Ampicillin resistant) carrying the secretion system (SoxS_promoter + RBS + HlyB + HlyD + TolC + Terminator). As a non-secretion control, E. coli harboring only the pSB1C3 vector with both sensor and effector systems was used.
Oxidative stress was induced by adding increasing concentrations of Paraquat (Methyl viologen dichloride hydrate - Sigma), an oxidative stress inducer in bacteria. The secretion was tested in cultures harboring A) and B) (Figure ) using 0 μM and 40 μM of Paraquat as described [http://2011.igem.org/Team:UNICAMP-EMSE_Brazil/Results#Methods above]. After 3 hours samples were collected, centrifuged (4000 rpm / 10 min; to avoid cell lysis) and the supernatant was collected and centrifuged again (13000 rpm / 10 min; to remove remaining cells). The supernatant fluorescence was measured in fluorometer (SLM – Aminco; 4 nm bandpass and 10 mm) with excitation in 500 nm and emission spectra from 508-550 nm. The GFP fluorescence was also detected in cells by fluorescence microscopy (Olympus).
Results
Microscopy data revealed GFP expression in the Paraquat induced cultures (Figure 2) but not in the non-induced one (Figure 3).
GFP secretion was confirmed by fluorescence emission and estimated to be approximately 6% of total protein, according to fluorescence levels. Significant levels of GFP fluorescence were found only in the supernatant of Paraquat induced cultures containing both the sensor/effector and the secretion systems but not in the non-induced cultures and in the cultures containing only the sensor/effector system (Figure 4).
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