Uptake of Choline and Its Conversion to Glycine Betaine by Bacteria in Estuarine Waters
Uptake of Choline and Its Conversion to Glycine Betaine by Bacteria in Estuarine Waters
复制标题
河口水域细菌对胆碱的吸收及其向甘氨酸甜菜碱的转化
DOI：
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发表时间：
1998
影响因子：
4.4
通讯作者：
R. Kiene
中科院分区：
文献类型：
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作者：
R. Kiene
摘要研究了纳摩尔水平的[甲基-14 C]胆碱在河口水样品和海水滤液培养物中的吸收和降解，所述海水滤液培养物主要由天然自由生活细菌组成。[14 C]胆碱的摄取表现出米氏动力学，滤液培养物中的Kt + Sn值为1.7至2.9 nM，河口水样中为1.7至4.1 nM。Vmax值范围为0.5 - 3.3 nM · h−1。因此，天然微生物群落中胆碱的摄取系统显示出非常高的亲和力，似乎能够在海水中预期的浓度下吸收这种化合物。一些天然结构类似物和对氯汞苯甲酸盐抑制胆碱的摄取，表明转运蛋白可能是多功能的，可能涉及巯基结合位点。当将11 nM [14 C]胆碱加入水样中时，在持续10至53 h的孵育中，显著部分（>50%）的甲基碳被呼吸为CO2。摄取[14 C]胆碱的细胞产生[14 C]甘氨酸甜菜碱（[14 C]GBT），并且高达80%的由细胞保留的放射性以GBT的形式存在，GBT是一种众所周知的渗透剂。滤液培养物中盐度的改变影响[14 C]胆碱降解或转化为[14 C]GBT的相对比例，而基本上不影响胆碱的总代谢。增加盐度从14到25或35 ppt导致更多的[14 C]GBT从胆碱，但更少的14 CO2产生比在控制。盐度降低到7 ppt时，[14 C]GBT的生成量减少，而14 CO2的生成量略有增加。[14 C]GBT在盐胁迫培养物中的细胞内积累是显著的（34 mM）。胆碱可以被河口细菌用作能量底物，也可以用作生物保护剂GBT的前体，特别是当细菌混合到高盐度沃茨中时。
ABSTRACT The uptake and degradation of nanomolar levels of [methyl-14C]choline in estuarine water samples and in seawater filtrate cultures composed mainly of natural free-living bacteria was studied. Uptake of [14C]choline exhibited Michaelis-Menten kinetics, withKt + Sn values of 1.7 to 2.9 nM in filtrate cultures and 1.7 to 4.1 nM in estuarine-water samples. Vmax values ranged from 0.5 to 3.3 nM · h−1. The uptake system for choline in natural microbial assemblages therefore displays very high affinity and appears able to scavenge this compound at the concentrations expected in seawater. Uptake of choline was inhibited by some natural structural analogs and p-chloromercuribenzoate, indicating that the transporter may be multifunctional and may involve a thiol binding site. When 11 nM [14C]choline was added to water samples, a significant fraction (>50%) of the methyl carbon was respired to CO2 in incubations lasting 10 to 53 h. Cells taking up [14C]choline produced [14C]glycine betaine ([14C]GBT), and up to 80% of the radioactivity retained by cells was in the form of GBT, a well-known osmolyte. Alteration of the salinity in filtrate cultures affected the relative proportion of [14C]choline degraded or converted to [14C]GBT, without substantially affecting the total metabolism of choline. Increasing the salinity from 14 to 25 or 35 ppt caused more [14C]GBT to be produced from choline but less 14CO2 to be produced than in the controls. Lowering the salinity to 7 ppt decreased [14C]GBT production and increased14CO2 production slightly. Intracellular accumulations of [14C]GBT in the salt-stressed cultures were osmotically significant (34 mM). Choline may be used as an energy substrate by estuarine bacteria and may also serve as a precursor of the osmoprotectant GBT, particularly as bacteria are mixed into higher-salinity waters.