Improvement of 5-aminolevulinic acid production by Rubrivivax benzoatilyticus PS-5 with self-flocculation by co-fermentation of precursors and volatile fatty acids under pH-controlled conditions

Abstract

Photosynthetic bacteria are known to utilize volatile fatty acids as a carbon source for growth and product formation. In this study, a new isolate, Rubrivivax benzoatilyticus PS-5, possessing self-flocculation properties, was cultivated in modified glutamate-malate (GM) medium containing glutamate and malate as carbon sources. The effect of acetic acid, propionic acid and butyric acid (at 1–4 g L−1) as co-substrates and 7.5 mM glycine, 10 mM succinic acid as precursors for 5-aminolevulinic acid (ALA) production from R. benzoatilyticus PS-5 was investigated. Among the volatile fatty acids tested, acetic acid was preferred to butyric acid and propionic acid, with the optimum concentrations of 3 g L−1, 1 g L−1 and 3 g L−1, respectively. The highest ALA production was 169.71 μM, 162.16 μM and 46.18 μM, respectively, while the highest productivity was 2.57 μM h−1, 2.25 μM h−1 and 0.96 μM h−1, respectively. The precursor was consumed completely (100 %) while the assimilation of the acetic acid and butyric acid was 62.50 % and 48.65 %, respectively. Supplementation of propionic acid (at 1–4 g l−1) had a negative effect on growth and ALA production. To increase production efficiency, the pH-control strategy (at pH 6.0–8.0) during fermentation was tested. The optimum pH was 7.0, giving the maximum ALA production of 286.18 μM and a productivity of 3.97 μM h−1. These values were 1.68-fold and 1.54-fold higher, respectively, than those under uncontrolled pH conditions.