Levander F, Rådström P
Applied Microbiology, Center for Chemistry and Chemical Engineering, Lund Institute of Technology, Lund University, SE-221 00 Lund, Sweden.
Appl Environ Microbiol. 2001 Jun;67(6):2734-8. doi: 10.1128/AEM.67.6.2734-2738.2001.
To study the influence of phosphoglucomutase (PGM) activity on exopolysaccharide (EPS) synthesis in glucose- and lactose-growing Streptococcus thermophilus, a knockout PGM mutant and a strain with elevated PGM activity were constructed. The pgmA gene, encoding PGM in S. thermophilus LY03, was identified and cloned. The gene was functional in Escherichia coli and was shown to be expressed from its own promoter. The pgmA-deficient mutant was unable to grow on glucose, while the mutation did not affect growth on lactose. Overexpression of pgmA had no significant effect on EPS production in glucose-growing cells. Neither deletion nor overexpression of pgmA changed the growth or EPS production on lactose. Thus, the EPS precursors in lactose-utilizing S. thermophilus are most probably formed from the galactose moiety of lactose via the Leloir pathway, which circumvents the need for a functional PGM.
为了研究磷酸葡萄糖变位酶（PGM）活性对嗜热链球菌在以葡萄糖和乳糖为生长底物时胞外多糖（EPS）合成的影响，构建了一个PGM基因敲除突变体和一个PGM活性升高的菌株。鉴定并克隆了嗜热链球菌LY03中编码PGM的pgmA基因。该基因在大肠杆菌中具有功能，并显示从其自身启动子表达。pgmA缺陷型突变体无法在葡萄糖上生长，而该突变不影响在乳糖上的生长。pgmA的过表达对以葡萄糖为生长底物的细胞中EPS的产生没有显著影响。pgmA的缺失或过表达均未改变在乳糖上的生长或EPS产生。因此，利用乳糖的嗜热链球菌中的EPS前体很可能是通过Leloir途径由乳糖的半乳糖部分形成的，该途径无需功能性PGM。
