5 Another source of information: protein leakage and the study of the secretome Available to Purchase

In order to investigate the potential occurrence of GFP leakage to the extracellular medium, the fluorescence and the total protein content of the supernatants coming from the different cultures have been investigated (Figures 4-1 and 4-2). In general, the fluorescence intensity of the supernatant increases in the case of the two biosensors and for all the operating conditions tested. However, a slightly lower extracellular fluorescence is observed in the case of the cultures operated in SDRs, compared with those operated in bioreactors without recycle loop. Consistent with this, Figure 4-2 shows that the amount of GFP protein as well as the fluorescent signal were significantly higher in the supernatant coming from a well-mixed bioreactor compared to a SDR, both harboring the fis::gfpAAV reporter. Similar results were obtained with the rrnB::gfpAAV construct (data not shown). The potential release of proteins to the extracellular medium is interesting since this phenomenon could possibly explain the long-term effect on expression of our gfp reporters. Interestingly, total extracellular protein concentration are consistent with the induction profile of the fis::gfpAAV biosensor previously reported (Figure 4-2 C and D to be compared with the GFP induction profiles of fis::gfpAAV depicted at Figure 3-7).