The use of NaCl addition for the improvement of polyhydroxyalkanoate production by Cupriavidus necator

• NaCl is a low cost and sustainable external stress that can enhance PHA production.
• NaCl addition at 9 g/l resulted in 30% more and an earlier PHA accumulation.
• Addition of 12 and 15 g/l NaCl were found to inhibit the production of PHA.
• A dielectric spectroscopy probe was able to indicate PHA accumulation in real-time.
• The window for maximum accumulation was detected by the probe avoiding polymer loss.

External stress factors in the form of ionic species or temperature increases have been shown to produce a stress response leading to enhanced PHA production. The effect of five different NaCl concentrations, namely 3.5, 6.5, 9, 12 and 15 g/l NaCl on PHA productivity using Cupriavidus necator has been investigated alongside a control (no added NaCl). A dielectric spectroscopy probe was used to measure PHA accumulation online in conjunction with the chemical offline analysis of PHA. The highest PHA production was obtained with the addition of 9 g/l NaCl, which yielded 30% higher PHA than the control. Increasing the addition of NaCl to 15 g/l was found to inhibit the production of PHA. NaCl addition can therefore be used as a simple, low cost, sustainable, non toxic and non reactive external stress strategy for increasing PHA productivity.