Hyperproduction of L-glutamate oxidase in submerged fermentation of Streptomyces sp N1 with culture pH control and calcium addition

Production of L-glutamate oxidase (GluOx) by Streptomyces sp. N1 was invest igated by controlling culture pH at 6.2, 6.7, 7.0, and 7.3 in a 5-L stirred fermenter. The corresponding GluOx activities obtained were 2.8, 4.2, 6.0, and 5.3 U/mL, respectively. Microbial growth was inhibited by increasing t he medium pH from 6.2 to 7.0. The inhibitory effect was also observed in pl ate colony growth under incubation with a different initial pH value. The e ffect of calcium on GluOx production was also studied in the pH-controlled bioreactor. When the culture pH was controlled at 6.2 or 7.0, GluOx product ion could not be improved or was only improved slightly by initial addition of calcium to the medium. However, when the culture pH was kept at 6.7, in itial Ca2+ addition (60 mM) conspicuously enhanced GluOx production up to 9 .3 U/mL, which was about twofold of that without Ca2+ addition. The enzyme production level was the highest ever reported in the literature. During fe rmentation the inhibition of cell growth by Ca2+ addition was observed. For the morphological changes, the cells mostly existed as pellets in the medi um without Ca2+ addition, whereas few pellets were found and almost all the cells were dispersed mycelia in the broth with Ca2+ addition.