Optimization of pH and glucose concentration of culture media for enhancement of hyaluronic acid production by Streptococcus equisimilis group C and G

Hyaluronic acid (HA) is a natural linear polysaccharide with excellent viscoelasticity, high water retention capacity and biocompatibility finding wide-range of application in medicine, drug delivery and cosmetics. Currently, microbial fermentation is used for industrial HA production. The present study reports screening and optimization of HA production by clinical Streptococcus equisimilis group C and G (GCS and GGS) isolates from Iranian patients.

The 11 S.equisimilis strains including 9 GCS and 2 GGS were characterized and primary HA production was quantified by carbazol assay. Accordingly, three strains were selected for further optimization. The effect of pH on HA yields at 12 points ranging from 3.1-7.5 and glucose concentrations ranging from 0.3-15 mg/ml at 11 points at optimized pH were determined for selected strains.

The range of HA concentration among 11 strains was 216.6-729.7 µg/ml. The three higher producer strains including GCS-08, GGS-88 and GGS132 with an average production of 573.0, 579.7 and 729.7 µg/ml, respectively was selected. The HA concentrations at optimized pH of selected strains were (6.5, 744.3 µg/ml), (4.8, 598.9 µg/ml) and (6.8, 1041.8 µg/ml) respectively. Cultivation at 15 mg/ml of glucose led to increasing HA yield by GCS-08:1096.4, GGS-88:1234.3 and GGS-132:1993.6 µg/ml.

The findings showed the significant effect of pH and direct correlation of glucose concentration on HA production that can increase the yield up to 2.73 folds. Identification of high producer strain at pH 4.8 would be an advantage for HA production under unusual condition at industrial scale.