Poly-β-hydroxybutyrate/ectoine co-production by ectoine-excreting strain Halomonas salina

• The co-production at low NaCl concentration avoided the inhibition of PHB synthesis.
• The excreted extracellular ectoine could escape from being degradating in the cells.
• In the non-growing phase, ectoine can still be synthesised and excreted efficiently.

The ectoine-excreting bacterial strain of Halomonas salina was employed in the co-production of poly-β-hydroxybutyrate (PHB) and ectoine (Ect) during a fermentation process (PHB/Ect co-production). An efficient PHB/Ect co-production process was carried out at low NaCl concentration (30 g L−1). It was established using 1H Nuclear Magnetic Resonance spectroscopy that H. salina produces PHB. The effects of the NaCl concentration, the initial C/N ratio, the phosphate concentration and mixed carbon sources were investigated with respect to PHB/Ect co-production. The PHB/Ect co-production system comprised growing and non-growing cell phases and was developed with NaCl concentration of 30 g L−1. The optimal conditions for PHB/Ect co-production by the ectoine-excreting strain of H. salina were 30 g L−1 NaCl, with an initial C/N ratio of 15, an initial phosphate concentration of 12 g L−1 and mixed carbon sources of 55 g L−1 glucose and 25 g L−1 monosodium glutamate. Using a PHB/Ect co-production system with growing and non-growing cell phases prevents the inhibition of PHB synthesis by high concentration of NaCl and significantly reduces ectoine degradation. PHB and ectoine concentrations as high as 35.3 g L−1 and 8.6 g L−1, respectively, were achieved. The efficient co-production of PHB and ectoine at a low NaCl concentration has been realised.