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首页> 外文期刊>Journal of bacteriology >Regulation of beta-galactoside transport and accumulation in heterofermentative lactic acid bacteria.
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Regulation of beta-galactoside transport and accumulation in heterofermentative lactic acid bacteria.

机译：调节半发酵乳酸菌中β-半乳糖苷的运输和积累。

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Galactose-grown cells of the heterofermentative lactic acid bacteria Lactobacillus brevis and Lactobacillus buchneri transported methyl-beta-D-thiogalactopyranoside (TMG) by an active transport mechanism and accumulated intracellular free TMG when provided with an exogenous source of energy, such as arginine. The intracellular concentration of TMG resultant under these conditions was approximately 20-fold higher than that in the medium. In contrast, the provision of energy by metabolism of glucose, gluconate, or glucosamine promoted a rapid but transient uptake of TMG followed by efflux that established a low cellular concentration of the galactoside, i.e., only two- to fourfold higher than that in the medium. Furthermore, the addition of glucose to cells preloaded with TMG in the presence of arginine elicited a rapid efflux of the intracellular galactoside. The extent of cellular TMG displacement and the duration of the transient effect of glucose on TMG transport were related to the initial concentration of glucose in the medium. Exhaustion of glucose from the medium restored uptake and accumulation of TMG, providing arginine was available for ATP generation. The nonmetabolizable sugar 2-deoxyglucose elicited efflux of TMG from preloaded cells of L. buchneri but not from those of L. brevis. Phosphorylation of this glucose analog was catalyzed by cell extracts of L. buchneri but not by those of L. brevis. Iodoacetate, at a concentration that inhibits growth and ATP production from glucose, did not prevent efflux of cellular TMG elicited by glucose. The results suggested that a phosphorylated metabolite(s) at or above the level of glyceraldehyde-3-phosphate was required to evoke displacement of intracellular TMG from the cells. Counterflow experiments suggested that glucose converted the active uptake of TMG in L. brevis to a facilitated diffusion mechanism that allowed equilibrium of TMG between the extra- and intracellular milieux. The means by which glucose metabolites elicited this vectorial regulation is not known, but similarities to the inducer expulsion that has been described for homofermentative Streptococcus and Lactobacillus species suggested the involvement of HPr, a protein that functions as a phosphocarrier protein in the phosphotransferase system, as well as a presumptive regulator of sugar transport. Indeed, complementation assays wit extracts of Staphylococcus aureus ptsH mutant revealed the presence of HPr in L. brevis, although this lactobacillus lacked a functional phaosphoenolpyruvate-dependent phosphortransferase system for glucose, 2-deoxyglucose, or TMG.
机译：短发酵乳酸杆菌和布氏乳杆菌的半乳糖生长细胞通过主动转运机制转运甲基-β-D-硫代半乳糖吡喃糖苷（TMG），并在提供外源能量（如精氨酸）时积累了细胞内游离TMG。在这些条件下产生的TMG的细胞内浓度比培养基中高约20倍。相反，通过葡萄糖，葡萄糖酸或氨基葡萄糖代谢提供的能量促进了TMG的快速但短暂的摄取，随后外排建立了低半乳糖苷的细胞浓度，即仅比培养基中高2至4倍。 。此外，在精氨酸存在下向预载TMG的细胞中添加葡萄糖会引起细胞内半乳糖苷的快速流出。细胞TMG置换的程度和葡萄糖对TMG转运的瞬时作用的持续时间与培养基中葡萄糖的初始浓度有关。如果精氨酸可用于ATP生成，则培养基中的葡萄糖耗尽将恢复TMG的摄取和积累。不可代谢的糖2-脱氧葡萄糖引起布氏乳杆菌预载细胞的TMG流出，但不引起短乳杆菌LMG的流出。该葡萄糖类似物的磷酸化是由布氏乳杆菌的细胞提取物催化的，而不是由短乳杆菌的细胞提取物催化的。碘乙酸盐的浓度可抑制葡萄糖的生长和ATP的产生，但不能阻止葡萄糖引起的细胞TMG流出。结果表明，需要磷酸化3-磷酸甘油醛或更高水平的磷酸化代谢物才能引起细胞内TMG从细胞中置换。逆流实验表明，葡萄糖将短乳杆菌中TMG的主动摄取转化为促进扩散的机制，使TMG在细胞外和细胞内环境之间达到平衡。葡萄糖代谢物引发这种矢量调控的方式尚不清楚，但与已描述的同型发酵链球菌和乳杆菌属物种的诱导物排出相似，表明HPr参与了这一工作，该蛋白在磷酸转移酶系统中起磷酸载体蛋白的作用。以及糖运输的推测性调节剂。确实，通过金黄色葡萄球菌ptsH突变体的提取物进行的互补分析显示，在短乳杆菌中存在HPr，尽管该乳酸菌缺乏葡萄糖，2-脱氧葡萄糖或TMG的功能性依赖磷酸烯醇丙酮酸的磷酸转移酶系统。

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