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首页> 外文期刊>Journal of bacteriology >Osmoregulation in Bacillus subtilis: synthesis of the osmoprotectant glycine betaine from exogenously provided choline.
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Osmoregulation in Bacillus subtilis: synthesis of the osmoprotectant glycine betaine from exogenously provided choline.

机译：枯草芽孢杆菌中的渗透调节：由外源性胆碱合成渗透保护剂甘氨酸甜菜碱。

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摘要

Exogenously provided glycine betaine functions as an efficient osmoprotectant for Bacillus subtilis in high-osmolarity environments. This gram-positive soil organism is not able to increase the intracellular level of glycine betaine through de novo synthesis in defined medium (A. M. Whatmore, J. A. Chudek, and R. H. Reed, J. Gen. Microbiol. 136:2527-2535, 1990). We found, however, that B. subtilis can synthesize glycine betaine when its biosynthetic precursor, choline, is present in the growth medium. Uptake studies with radiolabelled [methyl-14C]choline demonstrated that choline transport is osmotically controlled and is mediated by a high-affinity uptake system. Choline transport of cells grown in low- and high-osmolarity media showed Michaelis-Menten kinetics with Km values of 3 and 5 microM and maximum rates of transport (Vmax) of 10 and 36 nmol min-1 mg of protein-1, respectively. The choline transporter exhibited considerable substrate specificity, and the results of competition experiments suggest that the fully methylated quaternary ammonium group is a key feature for substrate recognition. Thin-layer chromatography revealed that the radioactivity from exogenously provided [methyl-14C]choline accumulated intracellularly as [methyl-14C]glycine betaine, demonstrating that B. subtilis possesses enzymes for the oxidative conversion of choline into glycine betaine. Exogenously provided choline significantly increased the growth rate of B. subtilis in high-osmolarity media and permitted its proliferation under conditions that are otherwise strongly inhibitory for its growth. Choline and glycine betaine were not used as sole sources of carbon or nitrogen, consistent with their functional role in the process of adaptation of B. subtilis to high-osmolarity stress.
机译：外源提供的甘氨酸甜菜碱在高渗透压环境中作为枯草芽孢杆菌的有效渗透保护剂。这种革兰氏阳性土壤生物体不能通过在确定的培养基中从头合成来增加甘氨酸甜菜碱的细胞内水平（A. M. Whatmore，J. A. Chudek，and R. H. Reed，J. Gen. Microbiol。136：2527-2535，1990）。然而，我们发现，当枯草芽孢杆菌的生物合成前体胆碱存在于生长培养基中时，它可以合成甘氨酸甜菜碱。放射性标记的[methyl-14C]胆碱的吸收研究表明，胆碱转运受渗透控制，并由高亲和力吸收系统介导。在低渗和高渗介质中生长的细胞的胆碱转运表现出Michaelis-Menten动力学，Km值为3和5 microM，最大转运速率（Vmax）分别为10和36 nmol min-1 mg蛋白-1。胆碱转运蛋白表现出相当大的底物特异性，竞争实验的结果表明，完全甲基化的季铵基团是底物识别的关键特征。薄层色谱法显示，外源提供的[甲基-14C]胆碱在细胞内累积的放射性为[甲基-14C]甘氨酸甜菜碱，表明枯草芽孢杆菌具有将胆碱氧化转化为甘氨酸甜菜碱的酶。外源提供的胆碱可显着提高枯草芽孢杆菌在高渗透压培养基中的生长速率，并使其在强烈抑制其生长的条件下增殖。胆碱和甘氨酸甜菜碱没有被用作碳或氮的唯一来源，这与它们在枯草芽孢杆菌适应高渗压力的过程中的功能作用相一致。

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