Institute of Life Sciences, Jiangsu University, Zhenjiang 212013, China.
BMC Microbiol. 2011 Feb 1;11(1):26. doi: 10.1186/1471-2180-11-26.
N-acylhomoserine lactone (AHL)-based quorum sensing (QS) systems have been described in many plant-associated Gram-negative bacteria to control certain beneficial phenotypic traits, such as production of biocontrol factors and plant growth promotion. However, the role of AHL-mediated signalling in the endophytic strains of plant-associated Serratia is still poorly understood. An endophytic Serratia sp. G3 with biocontrol potential and high levels of AHL signal production was isolated from the stems of wheat and the role of QS in this isolate was determined.
Strain G3 classified as Serratia plymuthica based on 16S rRNA was subjected to phylogenetic analysis. Using primers to conserved sequences of luxIR homologues from the Serratia genus, splIR and spsIR from the chromosome of strain G3 were cloned and sequenced. AHL profiles from strain G3 and Escherichia coli DH5α expressing splI or spsI from recombinant plasmids were identified by liquid chromatography-tandem mass spectrometry. This revealed that the most abundant AHL signals produced by SplI in E. coli were N-3-oxo-hexanoylhomoserine lactone (3-oxo-C6-HSL), N-3-oxo-heptanoylhomoserine lactone (3-oxo-C7-HSL), N-3-hydroxy-hexanoylhomoserine lactone (3-hydroxy-C6-HSL), N-hexanoylhomoserine lactone (C6-HSL), and N-heptanoyl homoserine lactone (C7-HSL); whereas SpsI was primarily responsible for the synthesis of N-butyrylhomoserine lactone (C4-HSL) and N-pentanoylhomoserine lactone (C5-HSL). Furthermore, a quorum quenching analysis by heterologous expression of the Bacillus A24 AiiA lactonase in strain G3 enabled the identification of the AHL-regulated biocontrol-related traits. Depletion of AHLs with this lactonase resulted in altered adhesion and biofilm formation using a microtiter plate assay and flow cells coupled with confocal laser scanning microscopy respectively. This was different from the closely related S. plymuthica strains HRO-C48 and RVH1, where biofilm formation for both strains is AHL-independent. In addition, QS in G3 positively regulated antifungal activity, production of exoenzymes, but negatively regulated production of indol-3-acetic acid (IAA), which is in agreement with previous reports in strain HRO-C48. However, in contrast to HRO-C48, swimming motility was not controlled by AHL-mediated QS.
This is the first report of the characterisation of two AHL-based quorum sensing systems in the same isolate of the genus Serratia. Our results show that the QS network is involved in the global regulation of biocontrol-related traits in the endophytic strain G3. However, although free-living and endophytic S. plymuthica share some conservation on QS phenotypic regulation, the control of motility and biofilm formation seems to be strain-specific and possible linked to the life-style of this organism.
已在许多与植物相关的革兰氏阴性细菌中描述了 N-酰基高丝氨酸内酯（AHL）为基础的群体感应（QS）系统，以控制某些有益的表型特征，例如生物防治因子的产生和植物生长促进。然而，AHL 介导的信号在与植物相关的鞘氨醇属内生菌株中的作用仍知之甚少。一种具有生物防治潜力和高水平 AHL 信号产生的内生鞘氨醇属 G3 菌株从小麦茎部分离出来，其 QS 作用已被确定。
基于 16S rRNA 将菌株 G3 分类为粘质沙雷氏菌，根据同源 luxIR 序列设计引物，从菌株 G3 的染色体中克隆并测序了 splIR 和 spsIR。通过液相色谱-串联质谱法鉴定了 G3 菌株和表达重组质粒中 splI 或 spsI 的大肠杆菌 DH5α 的 AHL 图谱。结果表明，SplI 在大肠杆菌中产生的最丰富的 AHL 信号是 N-3-氧代-己酰高丝氨酸内酯（3-氧代-C6-HSL）、N-3-氧代-庚酰高丝氨酸内酯（3-氧代-C7-HSL）、N-3-羟基-己酰高丝氨酸内酯（3-羟基-C6-HSL）、N-己酰高丝氨酸内酯（C6-HSL）和 N-庚酰高丝氨酸内酯（C7-HSL）；而 SpsI 主要负责合成 N-丁酰高丝氨酸内酯（C4-HSL）和 N-戊酰高丝氨酸内酯（C5-HSL）。此外，通过在 G3 菌株中异源表达 Bacillus A24 AiiA 内酯酶进行群体感应淬灭分析，鉴定了受 AHL 调控的生物防治相关性状。用这种内酯酶耗尽 AHLs 导致使用微量滴定板测定法和流动细胞与共聚焦激光扫描显微镜分别测定的粘附和生物膜形成发生改变。这与密切相关的粘质沙雷氏菌 HRO-C48 和 RVH1 菌株不同，这两种菌株的生物膜形成均不受 AHL 调控。此外，QS 正向调节 G3 菌株的抗真菌活性、外酶的产生，但负向调节吲哚-3-乙酸（IAA）的产生，这与之前在 HRO-C48 菌株中的报道一致。然而，与 HRO-C48 菌株不同的是，游泳运动不受 AHL 介导的 QS 调控。
这是首次对同一粘质沙雷氏菌属分离株中两种基于 AHL 的群体感应系统进行特征描述。我们的研究结果表明，QS 网络参与了内生菌株 G3 中生物防治相关性状的全局调控。然而，尽管自由生活和内生的粘质沙雷氏菌在 QS 表型调控上存在一些保守性，但运动和生物膜形成的控制似乎是菌株特异性的，可能与该生物体的生活方式有关。
