Improvements of poly(3-hydroxybutyrate) production in an air-lift reactor using simple production media

Abstract

Abstract Background Halomonas boliviensis is a halophilic microorganism that accumulates poly(3-hydroxybutyrate) (PHB) using different carbons sources when nitrogen is depleted from the culture medium. This work presents an improved production of PHB using an air-lift reactor (ALR) that was fed with a concentrated solution of a carbon source, and was supplemented with an adequate airflow rate. Results Simple production media were used to study PHB production by H. boliviensis in an ALR. Glucose was first used as the main carbon source and was fed during the exponential phase of cell growth. The maximum CDW and PHB content were 31.7 g/L and 51 wt%, respectively, when the airflow rate entering the reactor varied between 0.5 and 1.2 L/min. Changing the air inflow to 0.5–0.9 L/min resulted in an improvement in PHB accumulation (62 wt%). A cultivation was performed by using the latter range of airflow rate and feeding glucose only when nitrogen was depleted from the medium; a considerable enhancement in PHB content (72 wt%) and CDW (27 g/L) was achieved under these conditions. Moreover, PHB was also produced using molasses as the main carbon source. Residual cell mass was about the same to that achieved with glucose, however the PHB content (52 wt%) was lower. Conclusions PHB production by H. boliviensis in an ALR using a simple medium is possible. CDW and PHB content in H. boliviensis can be improved with respect to batch cultivations previously reported when a carbon source is fed to the reactor. The best strategy for the production of PHB consisted of starting the cultivation in a batch mode while glutamate was present in the medium; glucose should be fed when glutamate is depleted from the medium to keep an excess of the carbon source during the synthesis of PHB.

Keywords

• Poly(3-hydroxybutyrate)
• Halomonas boliviensis
• Air-lift reactor
• Halophilic bacterium