Klein W, Boos W
Department of Biology, University of Konstanz, Germany.
J Bacteriol. 1993 Mar;175(6):1682-6. doi: 10.1128/jb.175.6.1682-1686.1993.
Trehalose transport in Escherichia coli after growth at low osmolarity is mediated by enzyme IITre of the phosphotransferase system (W. Boos, U. Ehmann, H. Forkl, W. Klein, M. Rimmele, and P. Postma, J. Bacteriol. 172:3450-3461, 1990). The apparent Km (16 microM) of trehalose uptake is low. Since trehalose is a good source of carbon and the apparent affinity of the uptake system is high, it was surprising that the disaccharide trehalose [O-alpha-D-glucosyl(1-1)-alpha-D-glucoside] has no problems diffusing through the outer membrane at high enough rates to allow full growth, particularly at low substrate concentrations. Here we show that induction of the maltose regulon is required for efficient utilization of trehalose. malT mutants that lack expression of all maltose genes, as well as lamB mutants that lack only the lambda receptor (maltoporin), still grow on trehalose at the usual high (10 mM) trehalose concentrations in agar plates, but they exhibit the half-maximal rate of trehalose uptake at concentrations that are 50-fold higher than in the wild-type (malT+) strain. The maltose system is induced by trehalose to about 30% of the fully induced level reached when grown in the presence of maltose in a malT+ strain or when grown on glycerol in a maltose-constitutive strain [malT(Con)]. The 30% level of maximal expression is sufficient for maximal trehalose utilization, since there is no difference in the concentration of trehalose required for the half-maximal rate of uptake in trehalose-grown strains with the wild-type gene (malT+) or with strains constitutive for the maltose system [malT(Con)]. In contrast, when the expression of the lambda receptor is reduced to less than 20% of the maximal level, trehalose uptake becomes less efficient. Induction of the maltose system by trehalose requires metabolism of trehalose. Mutants lacking amylotrehalase, the key enzyme in trehalose utilization, accumulate trehalose but do not induce the maltose system.
大肠杆菌在低渗透压环境下生长后，海藻糖的转运由磷酸转移酶系统的酶IITre介导（W. 布斯、U. 埃曼、H. 福克尔、W. 克莱因、M. 林梅勒和P. 波斯特马，《细菌学杂志》172:3450 - 3461，1990年）。海藻糖摄取的表观Km（16微摩尔）较低。由于海藻糖是良好的碳源且摄取系统的表观亲和力较高，令人惊讶的是二糖海藻糖[O-α-D-葡糖基(1-1)-α-D-葡糖苷]能够以足够高的速率扩散穿过外膜，从而实现完全生长，尤其是在低底物浓度下。在此我们表明，麦芽糖操纵子的诱导对于海藻糖的有效利用是必需的。缺乏所有麦芽糖基因表达的malT突变体，以及仅缺乏λ受体（麦芽糖孔蛋白）的lamB突变体，在琼脂平板中通常的高（10毫摩尔）海藻糖浓度下仍能在海藻糖上生长，但它们在海藻糖摄取半最大速率时的浓度比野生型（malT +）菌株高50倍。麦芽糖系统被海藻糖诱导至约为在malT +菌株中在麦芽糖存在下生长或在麦芽糖组成型菌株[malT(Con)]中在甘油上生长时达到的完全诱导水平的30%。最大表达水平的30%足以实现最大程度的海藻糖利用，因为在具有野生型基因（malT +）的海藻糖生长菌株或麦芽糖系统组成型菌株[malT(Con)]中，摄取半最大速率所需的海藻糖浓度没有差异。相比之下，当λ受体的表达降低到最大水平的不到20%时，海藻糖摄取效率降低。海藻糖对麦芽糖系统的诱导需要海藻糖的代谢。缺乏海藻糖利用关键酶淀粉海藻糖酶的突变体积累海藻糖，但不诱导麦芽糖系统。
