不动杆菌属中aidE基因编码高丝氨酸内酯酶

群体感应(Quorum sensing,QS)是细菌在进化过程中形成的依赖于群体密度的细菌间交流方式。许多革兰氏阴性细菌以N-酰基高丝氨酸内酯(AHL)为信号分子,感应自身群体密度并调控致病基因表达。因此,淬灭AHLs信号分子可防治此类细菌引起的植物病害。本实验室前期已筛选得到了一株具有AHLs信号降解能力的不动杆菌菌株Acinetobacter sp.77,本研究通过基因组文库筛选,自菌株77中克隆得到具有AHLs降解活性的基因aidE。该基因编码268个氨基酸。序列一致性比较发现aidE的氨基酸序列与吉伦伯不动杆菌Acinetobacter gyllenbergii CIP110306中β-内酰胺酶一致性高达95%,但与已知的AHLs降解酶序列一致性较低,最高为缓黄分支杆菌Mycobacterium lentiflavum中AHL内酯酶Att M/Aii B家族蛋白(CQD23908.1),一致性仅为33%。通过高压液相色谱(HPLC)分析Aid E蛋白处理N-己酰基高丝氨酸内酯(C6-HSL)的反应产物,证明aidE为AHL内酯酶。序列比对研究发现,aidE基因在不动杆菌属中并不保守,其在菌株77基因组中的上下游的基因排列存在菌株水平的特异性,且aidE基因下游存在疑似IS插入序列,上述证据表明aidE基因有可能是通过水平转移进入Acinetobacter sp.77基因组中,或其在基因组中的位置发生过重排。表达aidE的软腐果胶杆菌Z3-3中完全检测不到AHLs信号产生,且致病力明显降低。综上所述,aidE为新发现的AHL内酯酶。在防治依赖QS系统表达致病性的细菌病害中具有应用潜力。

AidE encodes an N-acyl homoserine lactonase in Acinetobacter

Quorum sensing (QS) is a cell-cell communication mechanism that allows bacterial populations to coordinate gene expression in response to cell density. N-acylhomoserine lactones (AHL) are used as quorum-sensing signal molecules by many Gram negative bacteria. Acinetobacter sp. 77, an AHL-degrading bacterium, was isolated in our previous work. The gene aidE for AHL inactivation was cloned in this study by screening a genomic DNA library. The deduced protein AidE is 268 amino acids in length and shares a high identity (95%) with the beta-lactamase family protein in Acinetobacter gyllenbergii CIP110306, but low identities with known AHL-degrading enzymes. HPLC analysis of the AidE-degraded C6-HSL products revealed that AidE functioned as an AHL lactonase. Sequences alignment suggested that the aidE gene is not conserved in Acinetobacter species, flanking sequences of aidE and their arrangement are specific in Acinetobacter sp. 77 genome, and some IS insertion sequences were found downstream of the aidE gene. These evidences indicated that the aidE gene might be foreign DNA taken up via horizontal gene transferring or had changed its relative location due to the genome rear-arrangement. Expression of the aidE gene in Pectobacterium carotovorum subsp. carotovorum Z3-3 significantly reduced its AHL production as well as the pathogenicity on host plants, indicating that AidE was able to effectively quench quorum sensing-dependent functions in bacteria. In conclusion, aidE is a newfound AHL-lactonase with a potential for suppression of bacterial infections.