Abstract
BackgroundHalomonas 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.ResultsSimple 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.ConclusionsPHB 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.
Highlights
Halomonas boliviensis is a halophilic microorganism that accumulates poly(3-hydroxybutyrate) (PHB) using different carbons sources when nitrogen is depleted from the culture medium
We report PHB production by H. boliviensis that was grown in an air-lift reactor (ALR)
We found that the magnesium concentration can be reduced 20-fold and ammonium chloride can be removed from the medium composition, thereby monosodium glutamate (MSG) is left as the sole nitrogen source in the medium
Summary
Halomonas boliviensis is a halophilic microorganism that accumulates poly(3-hydroxybutyrate) (PHB) using different carbons sources when nitrogen is depleted from the culture medium. Poly(3-hydroxybutyrate) (PHB) is the most common type of the PHAs and has similar properties to polypropylene (Lee 1996; Harding et al 2007). The current industrial production of PHAs is still performed in small-scale (from 1000 to 20,000 tons per year) that increments the cost of the polymers (Chanprateep 2010). In this respect, the commercialization of PHB may be restricted to applications in tissue engineering and other biomedical appliances (Manavitehrani et al 2016) in which oil-derived plastics cannot be utilized. The dominant contribution to the environmental deterioration in the production of PHB is the large requirement for energy, steam for sterilization procedures, as well as high requirement of freshwater (Harding et al 2007)
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