Table 3.
Evaluation of antibiotic-free system in fermenters (production of rEPA protein)
| Induction at early stage of growth |
Induction at advanced stage of growth | |||
|---|---|---|---|---|
| System based on kana resistance | Antibiotic free system | System based on kana resistance | Antibiotic free system | |
| Cell dry weigh (g/L) | 28 | 23 | 22 | 24 |
| Plasmid retention (%) | 5 | 100 | 90 | 98 |
| Product yield (mg/L) | 36 | 350 | 280 | 603 |
| Specific productivity (mg product/gCDW) |
1 | 15 | 13 | 25 |
Two conditions have been analyzed: induction at A600 = 25 (advanced stage of growth), close to standard production, and induction at A600 = 1 (early stage of growth) to increase the number of cell division between induction and end of fermentation and introduce an extended high level of stress over the cells.
In normal conditions the plasmid maintenance is increased and productivity doubles. For extended stress condition, the differences between antibiotic-free and standard are dramatic, both in terms of plasmid maintenance and protein productivity.