TEMPERATURE PROFILES OF GELLAN GUM SYNTHESIS AND ACTIVITIES OF BIOSYNTHETIC-ENZYMES

Gellan-gum biosynthesis is temperature-dependent with a maximal production yield at 20-25 degrees C, which is well below the optimal range for growth (30-35 degrees C) of the producing strain Pseudomonas elodea (now considered Sphingomonas paucimobilis) A.T.C.C. 31461. As judged by viscometric measurements the highest-molecular-mass biopolymer is produced at 20 degrees C. The specific activity of the enzymes involved in the synthesis of the activated sugar precursors for gellan polymerization can be considered as partially responsible for the yield of this exopolysaccharide at temperatures within the range 20-35 degrees C. The dTDP-L-rhamnose biosynthetic enzyme system (TRS) exhibits the lowest specific activity and, in concert with UDP-D-glucose dehydrogenase (UGD), appears to limit gellan synthesis, particularly at temperatures above 30 degrees C. Phosphoglucose isomerase and phosphoglucomutase present the highest specific activities, significantly above the levels of UDP-D-glucose pyrophosphorylase (UGP) and dTDP-D-glucose pyrophosphorylase (TGP), which are otherwise much higher than those of UGD and TRS. In addition, UGD, and particularly TRS, are the most thermosensitive of the gellan-biosynthetic enzymes studied.