luxS and arcB control aerobic growth of Actinobacillus actinomycetemcomitans under iron limitation
luxS and arcB control aerobic growth of Actinobacillus actinomycetemcomitans under iron limitation
复制标题
DOI：
10.1128/iai.71.1.298-308.2003
复制
发表时间：
2003-01-01
影响因子：
3.1
通讯作者：
Demuth, DR
中科院分区：
文献类型：
--
作者：
Fong, KP;Gao, L;Demuth, DR
LuxS负责自身诱导物2(AI-2)的产生，AI-2在哈维氏弧菌中作为群体感应信号，控制细胞密度依赖的Lax操纵子的表达。在非发光生物中，AI-2的生理作用尚不清楚。我们报告说，在好氧、铁限制的条件下，放线菌伴生放线杆菌JP2中LuxS的失活会导致突变株的生长减少，但不会导致野生型生物的生长减少。在富铁条件下继代培养时，放线菌伴生放线菌JP2-12生长迟缓，细胞密度较高。此外，突变菌株在铁限制条件下，用含有LUXS功能拷贝的质粒转化后，生长到高密度。实时定量聚合酶链式反应结果显示，伴生放线菌JP2-12显著降低了AfuA(8倍)、feBCDE(10倍)和ftnAB(>；50倍)的表达，它们分别编码周质铁转运蛋白、柠檬酸铁转运蛋白和铁蛋白。可能的转铁蛋白、血红蛋白和血细胞结合蛋白受体的表达也在较适度的水平上减少(2-3倍)。相反，在LuxS突变体中，SIDD和frpB(编码可能的铁载体受体)的表达分别增加了10倍和3倍。为了更好地了解AI-2反应的机制，我们在放线菌基因组中搜索了哈维氏弧菌信号转导蛋白LuxP、LuxQ、LuxU和Luxo的同源基因。有趣的是，ArcB被发现与LuxQ传感器/激酶最相似。为了确定arcB是否在伴生放线杆菌对AI-2的反应中起作用，构建了一个arcB缺失的突变体。等位基因arcB突变体在厌氧条件下生长不佳，但在好氧富铁条件下生长正常。然而，arcB突变体在铁限制下不能有氧生长，逆转录酶PCR显示，arcB的失活导致了AfuA和ftnAB的表达下降。因此，伴生放线放线杆菌的同基因LuxS和arcB突变体在铁限制下有氧培养时表现出相似的表型，并且这两个突变体都表现出与铁的运输和储存有关的一组共同基因的表达降低。这些结果表明，LuxS和ArcB可能协同作用来控制伴生放线菌对铁限制条件的适应及其在这种条件下的生长。
LuxS is responsible for the production of autoinducer 2 (AI-2), which functions in Vibrio harveyi as a quorum-sensing signal that controls the cell density-dependent expression of the lax operon. In nonluminescent organisms, the physiologic role of AI-2 is not clear. We report that inactivation of luxS in Actinobacillus actinomycetemcomitans JP2 results in reduced growth of the mutant, but not the wild-type organism, under aerobic, iron-limited conditions. Stunted cultures of the luxS mutant A. actinomycetemcomitans JP2-12 grew to high cell density when subcultured under iron-replete conditions. In addition, the mutant strain grew-to high cell density under iron limitation after transformation with a plasmid containing a functional copy of luxS. Results of real-time PCR showed that A. actinomycetemcomitans JP2-12 exhibited significantly reduced expression of afuA (eightfold), fecBCDE (10-fold), and ftnAB (>50-fold), which encode a periplasmic ferric transport protein, a putative ferric citrate transporter, and ferritin, respectively. The expressions of putative receptors for transferrin, hemoglobin, and hemophore binding protein were also reduced at more modest levels (two- to threefold). In contrast, expressions of sidD and frpB (encoding putative siderophore receptors) were increased 10- and 3-fold, respectively, in the luxS mutant. To better understand the mechanism of the AI-2 response, the A. actinomycetemcomitans genome was searched for homologs of the V. harveyi signal transduction proteins, LuxP, LuxQ, LuxU, and LuxO. Interestingly, ArcB was found to be most similar to LuxQ sensor/kinase. To determine whether arcB plays a role in the response of A. actinomycetemcomitans to AI-2, an arcB-deficient mutant was constructed. The isogenic arcB mutant grew poorly under anaerobic conditions but grew normally under aerobic iron-replete conditions. However, the arcB mutant failed to grow aerobically under iron limitation, and reverse transcriptase PCR showed that inactivation of arcB resulted in decreased expression of afuA and ftnAB. Thus, isogenic luxS and arcB mutants of A. actinomycetemcomitans exhibit similar phenotypes when cultured aerobically under iron limitation, and both mutants exhibit reduced expression of a common set of genes involved in the transport and storage of iron. These results suggest that LuxS and ArcB may act in concert to control the adaptation of A. actinomycetemcomitans to iron-limiting conditions and its growth under such conditions.