Culture conditions affect the molecular weight properties of hyaluronic acid produced by Streptococcus zooepidemicus

Abstract

The effect of five culture variables on the molecular weight properties of hyaluronic acid (HA) produced by Streptococcus zooepidemicus was studied in batch culture with a complex medium containing glucose and 10 g of yeast extract per liter. Neither the culture pH (pH 6.3 to 8.0) nor the agitation speed (300 to 1,000 rpm) affected the weight-average molecular weight (M(w) of HA under anaerobic conditions at 37°C when 20 g of glucose per liter was used initially. M(w) was in the narrow range of 1.5 x 106 to 2.3 x 106, and polydispersity (P) was between 1.8 and 2.5. When S. zooepidemicus was grown at lower temperatures or with aeration, higher-molecular-weight polymer and increased yields were observed. The polydispersity, however, remained unaffected. Anaerobically, the mean M(w) (based on three samples taken within 4 h of glucose exhaustion) was (2.40 ± 0.10) x 106 and (1.90 ± 0.05) x 106 at 32 and 40°C respectively. Aeration of the culture at 1 vol/vol/min produced HA with mean M(w) of (2.65 ± 0.05) x 106 compared with (2.10 ± 0.10) x 106 under equivalent anaerobic conditions. The initial glucose concentration had the most pronounced effect on polymer characteristics. Increasing this concentration from 20 to 40 g/liter produced HA with mean M(w) of (3.1 ± 0.1) x 106 at 1-vol/vol/min aeration. The molecular weight of HA also exhibited time dependency, with smaller chains (M(w), ca. 2.5 x 106) detected early in the culture time course, rising to a maximum (M(w), 3.2 x 106) in the late exponential phase of growth. The mean polydispersity was also greater (2.7 ± 0.1) under these conditions. Replicate experiments performed under conditions resulting in the lowest (40°C, anaerobic) and highest (40 g of glucose per liter, 1-vol/vol/min aeration)-M(w) polymer demonstrated excellent experimental reproducibility.