镁、锰离子对黄原胶生物合成的影响

Effects of Mg^(2+) and Mn^(2+) on Biosynthesis of Xanthan Gum

通过添加不同浓度镁、锰的一系列摇瓶实验,研究野油菜黄单胞菌代谢过程中的关键酶:葡萄糖-6-磷酸脱氢酶(G-6-PDH)和丙酮酸激酶(PYK)的活性变化,确定最佳单因素金属离子添加方案:Mg2+添加量0.4g/100ml、Mn2+添加量0.04g/100ml,随后进行罐发酵实验,从而对摇瓶实验结果进行验证并研究金属离子对黄原胶罐发酵生物合成的影响。实验结果表明:0.4g/100ml Mg2+可以较大程度提高G-6-PDH的活性,与摇瓶实验结果基本一致;0.04g/100ml Mn2+大大提高了PYK的活性,与摇瓶实验结果一致;5L发酵罐中发酵液残糖总体呈下降趋势,在60h以后趋向平稳,Mg2+、Mn2+会一定程度上增加发酵液中残糖含量,从而降低碳源的利用率。

Glucose-6-phosphate dehydrogenase （G-6-PDH） and pyruvate kinase （PYK） are the key enzymes in the metabolism ofXanthomonas campestris that critically affect the xanthan gum biosynthesis. This study focused on the effects of Mg^2＋ and Mn^2＋ 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 Mg^2＋ and Mn^2＋ 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 Mg^2＋ notably elevated the activity of G-6-PDH, while the addition of 0.04 g/100 ml Mn^2＋ 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, Mg^2＋ and Mn^2＋ may reduce the content of residual sugar to a certain degree and promote the utilization of carbon source.