De Baets S, Du Laing S, François C, Vandamme E J
Department of Biochemical and Microbial Technology, Ghent University, Coupure Links 653, Ghent B-9000, Belgium.
J Ind Microbiol Biotechnol. 2002 Oct;29(4):181-4. doi: 10.1038/sj.jim.7000276.
In liquid culture conditions, the yeast-like fungus Tremella mesenterica occurs in the yeast state and synthesizes an exopolysaccharide (EPS) capsule, which is eventually released into the culture fluid. It is composed of an alpha-1,3-D-mannan backbone, to which beta-1,2 side chains are attached, consisting of D-xylose and D-glucuronic acid. Potato dextrose broth (PDB) seemed to be an excellent medium for both growth of the yeast cells and synthesis of the EPS. This medium is composed solely of an extract of potatoes to which glucose was added. Yet an important disadvantage of this production medium is the presence of starch in the potato extract, since Tremella cells are not capable of metabolizing this component; furthermore, it coprecipitates upon isolation of the polymer [3]. In this respect, it was essential to remove the starch in order to achieve high polysaccharide production and recovery. A good method was the removal of starch through ultrafiltration of the PDB medium before inoculation of the strain. This resulted in an excellent starch-free medium in which other components essential for polysaccharide production were still present [3]. Through implementation of single and cyclic fed-batch fermentations with glucose feed, 1.6- and 2.2-fold increases in EPS yield were obtained, respectively. Lowering the carbon source level by using a cyclic fed-batch technique might decrease the osmotic effect of glucose or any catabolite regulation possibly exerted by this sugar on enzymes involved in EPS synthesis.
在液体培养条件下,类酵母真菌银耳以酵母状态存在并合成一种胞外多糖(EPS)胶囊,最终释放到培养液中。它由α-1,3-D-甘露聚糖主链组成,β-1,2侧链连接在主链上,侧链由D-木糖和D-葡萄糖醛酸组成。马铃薯葡萄糖肉汤(PDB)似乎是酵母细胞生长和EPS合成的优良培养基。这种培养基仅由添加了葡萄糖的马铃薯提取物组成。然而,这种生产培养基的一个重要缺点是马铃薯提取物中存在淀粉,因为银耳细胞不能代谢这种成分;此外,在聚合物分离时它会共沉淀[3]。在这方面,为了实现高多糖产量和回收率,去除淀粉至关重要。一种好方法是在接种菌株之前通过对PDB培养基进行超滤来去除淀粉。这产生了一种优良的无淀粉培养基,其中仍存在多糖生产所需的其他成分[3]。通过实施单次和循环补料分批发酵并添加葡萄糖,EPS产量分别提高了1.6倍和2.2倍。使用循环补料分批技术降低碳源水平可能会降低葡萄糖的渗透效应或这种糖可能对参与EPS合成的酶施加的任何分解代谢调节。