Adaptation of sucrose metabolism in the Escherichia coli wild-type strain EC3132
Adaptation of sucrose metabolism in the Escherichia coli wild-type strain EC3132
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DOI：
10.1128/jb.184.19.5307-5316.2002
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发表时间：
2002-10-01
影响因子：
3.2
通讯作者：
Lengeler, JW
中科院分区：
文献类型：
--
作者：
Jahreis, K;Bentler, L;Lengeler, JW
虽然大肠杆菌菌株EC 3132具有染色体编码的蔗糖代谢途径，但其在低蔗糖浓度（5 mM）下的生长异常缓慢，倍增时间为20 h。在这份报告中，我们描述了相应的esc基因和相邻基因的亚克隆和进一步的表征。esc调节子包含蔗糖通透酶、果糖激酶和蔗糖水解酶的三个基因（分别为基因cscB、cscK和cscA）。这些基因排列在两个操纵子中，并在转录水平上由阻遏物CscR负控制。此外，csc基因表达被发现是环AMP-CrpA依赖性的。比较了大肠杆菌的基因组序列。大肠杆菌菌株EC 3132、K-12和O 157：H7以及沙门氏菌鼠伤寒血清型LT 2的研究表明，csc基因位于肠细菌染色体重排的热点区域。比较结果进一步表明，csc基因可能是最近才转移到大肠杆菌中的。coli野生型EC 3132的菌株，在不同的肠道细菌菌株分化的时间附近。我们发现的证据表明，一个移动的遗传因素，它使用的基因argW的位点特异性整合到染色体中，可能参与了这种水平的基因转移和CSC基因仍处于最佳适应新的主机的过程中。选择这样的适应性突变体生长速度更快的低蔗糖浓度得到三种不同类型的突变体。一类包含cscR（Con）突变，其组成性地表达所有csc基因。第二类构成了一个cscKo操纵基因突变，它成为诱导型的CSC基因表达在低蔗糖浓度。第三类被发现是一个突变的蔗糖通透酶，导致运输活动的增加。
Although Escherichia coli strain EC3132 possesses a chromosomally encoded sucrose metabolic pathway, its growth on low sucrose concentrations (5 mM) is unusually slow, with a doubling time of 20 h. In this report we describe the subcloning and further characterization of the corresponding esc genes and adjacent genes. The esc regulon comprises three genes for a sucrose permease, a fructokinase, and a sucrose hydrolase (genes cscB, cscK, and cscA, respectively). The genes are arranged in two operons and are negatively controlled at the transcriptional level by the repressor CscR. Furthermore, csc gene expression was found to be cyclic AMP-CrpA dependent. A comparison of the genomic sequences of the E. coli strains EC3132, K-12, and O157:H7 in addition to Salmonella enterica serovar Typhimurium LT2 revealed that the csc genes are located in a hot spot region for chromosomal rearrangements in enteric bacteria. The comparison further indicated that the csc genes might have been transferred relatively recently to the E. coli wild-type EC3132 at around the time when the different strains of the enteric bacteria diverged. We found evidence that a mobile genetic element, which used the gene argW for site-specific integration into the chromosome, was probably involved in this horizontal gene transfer and that the csc genes are still in the process of optimal adaptation to the new host. Selection for such adaptational mutants growing faster on low sucrose concentrations gave three different classes of mutants. One class comprised cscR(Con) mutations that expressed all csc genes constitutively. The second class constituted a cscKo operator mutation, which became inducible for csc gene expression at low sucrose concentrations. The third class was found to be a mutation in the sucrose permease that caused an increase in transport activity.