Abstract:

Glucose-6-phosphate dehydrogenase (G-6-PDH) and pyruvate kinase (PYK) are the key enzymes in the metabolism of Xanthomonas campestris that critically affect the xanthan gum biosynthesis. This study focused on the effects of Mg2+ and Mn2+ concentrations on G-6-PDH and PYK activities and sugar residue during shake flask cultivation and fermentor cultivation of Xanthomonas campestris2HL. The optimal concentrations of Mg2+ and Mn2+ in the shake flask cultivation were confirmed as 0.4 g/100 ml and 0.04 g/100 ml, respectively. Then fermentor cultivation was carried out to verify the results of shake flask cultivation to further study the effects of the two metal ions on biosynthesis of xanthan gum in the scale-up fermentation. The results indicated that the addition of 0.4 g/100 ml Mg2+ notably elevated the activity of G-6-PDH, while the addition of 0.04 g/100 ml Mn2+ increased the activity of pyruvate kinase to a great degree, which both were coincident with the results of shake flask cultivation. During the early fermentor cultivation the residual sugar generally tended to decrease but to be stable after 60 h. Therefore, Mg2+ and Mn2+ may reduce the content of residual sugar to a certain degree and promote the utilization of carbon source.

Key words: Xanthomonas campestris, metal ion, glucose-6-phosphate dehydrogenase, pyruvate kinase, residual sugar