Baisuo Zhao, Tel: +86-10-82106784;E-mail:
在嗜盐细菌盐适应中,四氢嘧啶(1,4,5,6-四氢-2-甲基-4-嘧啶羧酸)和羟基四氢嘧啶(1,4,5,6-四氢-2-甲基-5-羟基-4-嘧啶羧酸)发挥着十分重要的作用。四氢嘧啶的生物合成以L-天冬氨酸-
Ectoine[(S)-2-methyl-1,4,5,6-tetrahydropyrimidine-4-carboxylic acid] and its hydroxyectoine[(S, S)-2-methyl-5-hydroxy-1,4,5,6-tetrahydropyrimidine-4-carboxylic acid] play a crucial role in the salt adaptation mechanism in halophilic bacteria. The biosynthesis of ectoine is catalyzed by three enzymes: L-diaminobutyric acid aminotransferase (EctB), L-diaminobutyric acid acetyltransferase (EctA), and ectoine synthase (EctC). Using L-Aspartate-
栖息于高盐环境中的嗜盐菌,通过从外界环境中吸收或自身生物合成来积累一些易溶的、低分子量的有机溶质以抵御外界的渗透胁迫。这些在生理pH范围内不带电荷,且能与细胞内体系相容,而不影响其它生物大分子功能的溶质被称为“相容性溶质”[
四氢嘧啶(Ectoine,1,4,5,6-四氢-2-甲基-4-嘧啶羧酸,C6H10N2O2,MW=142.16)于1985年首次在极端嗜盐光合细菌盐绿需盐红螺菌(
四氢嘧啶(A)和羟基四氢嘧啶(B)的结构示意图
Structures of ectoine (A) and hydroxyectoine (B).
高盐或盐波动条件下,大多数嗜盐细菌常常从外部吸收四氢嘧啶类相容性溶质来维持细胞内的高渗透压,当环境中缺乏甜菜碱和四氢嘧啶等相容性溶质时,一些嗜盐细菌可以从头合成四氢嘧啶类进行渗透调节[
嗜盐细菌中四氢嘧啶和羟基四氢嘧啶的合成途径
Synthetic pathways of ectoine and hydroxyectoine in halophilic bacteria.
在嗜盐细菌中,编码四氢嘧啶生物合成相关酶的3个基因通常位于
[
基于16S rRNA基因序列的四氢嘧啶合成嗜盐细菌的亲缘图
Phylogenetic relationship based on 16s rRNA gene sequences of halophilic bacteria that synthesize ectoine. The scale bar indicates the phylogenetic distance.
合成四氢嘧啶类物质的嗜盐细菌
Halophilic bacteria that synthesize ectoine
Species | Accession number | Na+ opt./% |
Na+/%( |
pH opt. | pH |
The blue background shown in Table 1 indicates the halophilic bacterium can synthesize both ectoine and glycine betaine. The white background shown in Table 1 the halophilic bacterium can synthesize ectoine, but not glycine betaine. ND: data were not shown in the published paper. | |||||
AQUI01000002]]> | 15.0-20.0]]> | 12.0-30.0]]> | 7.5]]> | 6.0-8.0]]> | |
AM286690]]> | 3.0-10.0]]> | 1.0-12.5]]> | ND]]> | ND]]> | |
CP003466]]> | 3.0-7.5]]> | 1.0-15.0]]> | ND]]> | ND]]> | |
AJGP01000039]]> | 3.0-5.0 ]]> | 0.5-12.0 ]]> | 7.5]]> | ND]]> | |
AJ493660]]> | 15.0]]> | 1.0-20.0]]> | 9.0]]> | 7.0-10.0]]> | |
KX618877]]> | 8.3-12.0]]> | 4.3-24.0]]> | 7.5]]> | 6.0-10.5]]> | |
M26631]]> | 15.0]]> | 6.0-20.0]]> | 6.5-7.5]]> | 6.0-8.0]]> | |
ATXK01000033 | 3.2 | ND | ND | ND | |
DQ504377]]> | 12.0]]> | 8.0-33.0]]> | 7.2]]> | 6.0-9.5]]> | |
AM492159]]> | 7.0]]> | 3.0-20.0]]> | 8.5]]> | 5.8-11.0]]> | |
ABHZ01000019]]> | 2.4-6.0]]> | 2.0-22.0]]> | ND]]> | 8.5-10]]> | |
KM066107]]> | 6.3]]> | 1.3-25.3]]> | 8.5-9.5]]> | 6.5-10.0]]> | |
CP000285]]> | 7.5-10.0]]> | 0.9-25.0]]> | 7.5]]> | 5.0-10.0]]> | |
AF118021]]> | 2.5-3.5]]> | 1.5-12.0]]> | ND]]> | ND]]> | |
AM942722 | ND | 0.9-6.0 | ND | ND | |
AJ316208 | ND | 2.0-8.0 | ND | ND | |
CP002858]]> | 3.0]]> | 3.0-18.0]]> | 6.0-8.0]]> | ND]]> | |
JMLV01000013]]> | 5.0]]> | 1.5-20.0]]> | 7.5]]> | 6.5-8.5]]> | |
DQ664540]]> | 5.0-7 .0]]> | 1.0-18.0]]> | 7.5-8.0]]> | 5.5-10.0]]> | |
AQXX01000025]]> | 4.0-6 .0]]> | 1.0-10.0]]> | 7.0-8.0]]> | 5.0-10.0]]> | |
HE717023]]> | 5.9-8.8]]> | 3.0-12.0]]> | 7.5]]> | 5.5-10.0]]> | |
AB195680]]> | 6 .0]]> | 0.5-25.0 ]]> | 7.5-8.0]]> | 5.5-10.0]]> | |
AZUQ01000001]]> | 8.0-12.0]]> | 3.0-18 .0]]> | 7.0-7.5]]> | 5.0-9.0]]> | |
ASTJ01000004]]> | 7.5]]> | 0.5-15.0]]> | ND]]> | 6.0-9.0]]> | |
FN869568]]> | 3.5-8.0]]> | 3.5-20.0]]> | 7.2]]> | 5.0-9.0]]> | |
AJ417388]]> | 3.0-6.0]]> | 0.5-15.0]]> | 7.5-8.5]]> | 5.0-11.0]]> | |
EU218533]]> | 10.0]]> | 2.0-17.5]]> | 6.5]]> | 6.0-9.0]]> | |
AMQY01000015]]> | 10.0]]> | 5.0-25.0]]> | 7.0-8.0]]> | 5.0-10.0]]> | |
ARKK01000003]]> | 5.0-10.0]]> | 1.0-20.0]]> | 7.5]]> | 5.0-9.0]]> | |
KM066108]]> | 8.3]]> | 1.3-25.0]]> | 6.0-10.0]]> | 8.0-8.5]]> | |
FJ429198]]> | 3.0-5.0]]> | 1.0-20.0]]> | 7.5]]> | 6.0-10.5]]> | |
CP000544]]> | 15.0-35.0]]> | 3.0-35.0]]> | 7.4-7.9]]> | ND]]> | |
AM941746]]> | 10.0]]> | 5.0-17.5]]> | 7.0-8.0]]> | 5.5-8.5]]> | |
AXBE01000001 | ND | 1.0-7 .0 | 6.5-8.0 | 5.5-9.0 | |
CP006773 | 3.5 | 1.5-6.5 | 7.7 | 6.0-8.8 | |
AB127980]]> | 10.0]]> | 3.0-30 .0]]> | 7.0]]> | 5.0-9.0]]> | |
jgi.1055387]]> | 2.0-4.0 ]]> | 1.0-6.0]]> | 6.5-7.5]]> | 6.0-8.0]]> | |
640721707 | 5.0 | 0-20.0 | 7.3 | 5.0-10.0 | |
AY517633]]> | 2.0-6.0 ]]> | 0-18.0]]> | 7.0-8.0]]> | 5.5-ND]]> | |
FO203363]]> | 3.5]]> | 0.5-20.0]]> | 7.0-7.5]]> | 6.0-9.5]]> | |
AY563030]]> | ND]]> | 3.0-12 .0]]> | ND]]> | 5.3-8.8]]> | |
jgi.1107934]]> | 2.0-5.0 ]]> | 1.0-10.0]]> | 6.5-7.5]]> | 6.0-8.0]]> | |
AJ627909]]> | 6.0]]> | 1.0-6.0]]> | 8.0]]> | 7.0-12.5]]> | |
2576860715 | 2.0-3.0 | 0.5-10 .0 | 8.0 | 6.5-10.0 | |
AB006769 | 3.0 | 0.5-9.0 | 8.0 | 7.0-10.5 | |
AY619715]]> | 5.0-8 .0]]> | 0-18.0]]> | 7.2]]> | 6.0-9.0]]> | |
AY619712]]> | 5.0-8.0]]> | 0-18.0]]> | 7.2]]> | 6.0-9.0]]> | |
AY373031]]> | 10 .0]]> | 3.0-20.0]]> | 7.2]]> | 6.0-9.0]]> | |
AVPF01000156]]> | 2.0-5.0]]> | 1.0-9.0]]> | 7.0-7.5]]> | 6.0-9.0]]> | |
AUVB01000024 | 3.5 | 0.7-4.2 | 8.0 | 5.0-9.0 | |
AICX01000084]]> | 10.0]]> | 10.0-30.0]]> | ND]]> | 6.0-9.0]]> | |
2510465783]]> | 10.0]]> | 5.0-20.0]]> | ND]]> | ND]]> | |
EF177692]]> | 10.0]]> | 1.0-30.0]]> | 8.5]]> | 6.0-10.0]]> | |
ARRM01000007]]> | 3.0-6 .0]]> | 0.5-20 .0]]> | ND]]> | 6.0-10.0]]> | |
AM492160]]> | 10.0]]> | 3.0-20 .0]]> | 8.5]]> | 5.8-10.0]]> | |
AXBG01000021]]> | 1.0-4.0]]> | 0.6-6.0 ]]> | 7.0-8.5]]> | 6.0-9.3]]> | |
AGBF01000432]]> | 4.0]]> | 4.0-7.0]]> | 7.5]]> | 5.0-11.0]]> | |
AGRZ01000060 | 4.7-8.2 | 3.0-10.0 | 8.8-9.8 | 8.0-10.8 | |
2774822901 | 2.0-4.0 | 0-15.0 | 6.0-7.0 | 5.0-11.0 | |
AM294944 | ND | 2.0-10.0 | 7.2 | ND | |
AY186195]]> | 3.0-4.0]]> | 2.0-8.0]]> | ND]]> | ND]]> | |
CP004388]]> | 2.0-4.0]]> | 0.5-10.0]]> | ND]]> | ND]]> |
嗜盐细菌的盐适应机制极为复杂,在应对外界盐度变化时,几种相容性溶质相辅相成,作为最为重要的2种相容性溶质,四氢嘧啶类和甜菜碱类密切相关。我们得到的67株四氢嘧啶合成菌株中就有51株同时具备甘氨酸甜菜碱合成能力(
四氢嘧啶类的生物学功能在多种类型的嗜盐细菌中均有报道,但由于“嗜盐细菌”并不是分类学意义上的专有名词,且不同来源的嗜盐细菌在生理特性上具有一定的差异,四氢嘧啶类与其他相容性溶质在盐适应和盐胁迫过程中的功能也有所区别。因而我们仅选取了部分代表性的四氢嘧啶类合成嗜盐细菌进行了分析归纳,对四氢嘧啶及羟基四氢嘧啶在盐适应过程中的作用进行系统的阐述。
作为革兰氏阴性嗜盐细菌的模式菌株,伸长盐单胞菌在高盐条件下以四氢嘧啶类作为主要的相容性溶质,
四氢嘧啶类相容性溶质的重要作用不只局限于平衡嗜盐细菌细胞内外渗透压上,二者也可作为细胞稳定剂提高菌体对于高温、干燥、冻融处理,甚至是紫外线辐射、细胞毒素等压力的抵抗作用[
目前,随着四氢嘧啶类独特的生物学功能被不断的深入挖掘,四氢嘧啶类合成基因在生物学技术应用领域也越来越受到广泛的关注[
(1) 四氢嘧啶类合成基因应用于构建基因工程菌。Louis等(1997)首次将嗜盐海球菌
(2)
四氢嘧啶类合成基因应用于转基因农作物。土壤盐分是造成农业用地流失和农作物减产的主要环境因素之一,因而四氢嘧啶合成基因在转基因经济作物中具有极高的应用价值。Nakayama等将
不耐盐菌体中四氢嘧啶类生物合成基因的导入,显著提高了宿主对高盐高渗环境的应对能力,使其在盐胁迫下可以稳定生长并发挥其生理功能,作为分子生物学的有力工具更加广泛地应用于生产实践。长期以来,产量低、生产成本高一直制约着四氢嘧啶类在各领域的实际应用,因而四氢嘧啶类的高效异源表达为其合成与工业化生产提供了更多可能性。同时,四氢嘧啶生物合成基因在植物中的成功表达增强了转基因作物的耐盐碱性,对干旱盐碱土地的治理具有深远的意义。
嗜盐细菌的盐适应机制是极为复杂的一个过程,在盐波动下往往需要1种以上的相容性溶质共同发挥作用以抵御外界的高渗透环境。四氢嘧啶和羟基四氢嘧啶作为一类极为重要的相容性溶质,在此过程中起着重要的作用。二者与其他相容性溶质如何相互影响,盐适应过程中四氢嘧啶类又具有怎样的独特性?为何一些四氢嘧啶合成菌株可以同时合成甘氨酸甜菜碱,而另一些菌株却不含有甜菜碱合成基因,究竟嗜盐细菌更偏向于利用哪类相容性溶质作为渗透保护剂,这种倾向与外界盐度又有何联系?此外,虽然羟基四氢嘧啶是四氢嘧啶的衍生物,化学结构上密切相关,但二者的渗透保护功能却不尽相同,这是否与其微小的结构差异有关,它们在渗透调节中的作用又有何规律?目前,虽然我们对嗜盐细菌中四氢嘧啶类的生物合成过程及其生理功能有了一定的了解,但是当外界盐度升高时,细胞如何感知外界盐度的变化、信息如何传递到细胞内、生物合成及转运的调控机制如何触发、以及四氢嘧啶类物质的转运与代谢等诸多环节尚不明确。这些问题对于我们认识和比较不同类别嗜盐细菌之间的亲缘关系至关重要,更是四氢嘧啶类合成基因资源开发与应用的关键,有待相关研究者的深入探究。
四氢嘧啶和羟基四氢嘧啶表现出了巨大的应用价值和商业前景,其生物合成基因在构建基因工程菌、现代食品工业、化妆品领域、医学应用、污水处理和石油污染生物修复、微生物电池等方面得到广泛应用,但在转基因植物开发领域仍处于初步探索状态。我国盐碱土地面积辽阔,四氢嘧啶类基因的研究和应用可为增强干旱盐碱地区农作物的抗逆性提供优质资源。因此,有望本综述可以促进四氢嘧啶类生物合成基因在代谢组学、蛋白组学、分子进化等生物技术领域更为深入的研究,促进四氢嘧啶类相容性溶质在干旱盐碱环境的改良和治理等领域更为广泛的应用。
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