Eberl L
Lehrstuhl für Mikrobiologie, Technische Universität München, Freising, Germany.
Syst Appl Microbiol. 1999 Dec;22(4):493-506. doi: 10.1016/S0723-2020(99)80001-0.
The view of bacteria as unicellular organisms has strong roots in the tradition of culturing bacteria in liquid media. However, in nature microbial activity is mainly associated with surfaces where bacteria form highly structured and cooperative consortia which are commonly referred to as biofilms. The ability of bacteria to organize structurally and to distribute metabolic activities between the different members of the consortium demands a high degree of coordinated cell-cell interaction. Recent work has established that many bacteria employ sophisticated intercellular communication systems that rely on small signal molecules to control the expression of multiple target genes. In Gram-negative bacteria, the most intensively investigated signal molecules are N-acyl-L-homoserine lactones (AHLs), which are utilized by the bacteria to monitor their own population densities in a process known as 'quorum sensing'. These density-dependent regulatory systems rely on two proteins, an AHL synthase, usually a member of the LuxI family of proteins, and an AHL receptor protein belonging to the LuxR family of transcriptional regulators. At low population densities cells produce a basal level of AHL via the activity of an AHL synthase. As the cell density increases, AHL accumulates in the growth medium. On reaching a critical threshold concentration, the AHL molecule binds to its cognate receptor which in turn leads to the induction/repression of AHL-regulated genes. To date, AHL-dependent quorum sensing circuits have been identified in a wide range of gram-negative bacteria where they regulate various functions including bioluminescence, plasmid conjugal transfer, biofilm formation, motility, antibiotic biosynthesis, and the production of virulence factors in plant and animal pathogens. Moreover, AHL signal molecules appear to play important roles in the ecology of complex consortia as they allow bacterial populations to interact with each other as well as with their eukaryotic hosts.
将细菌视为单细胞生物的观点在液体培养基中培养细菌的传统中有着深厚的根源。然而，在自然界中，微生物活动主要与细菌形成高度结构化和协作性聚集体的表面相关，这些聚集体通常被称为生物膜。细菌在结构上进行组织并在聚集体的不同成员之间分配代谢活动的能力需要高度协调的细胞间相互作用。最近的研究表明，许多细菌采用复杂的细胞间通讯系统，这些系统依赖于小信号分子来控制多个靶基因的表达。在革兰氏阴性细菌中，研究最深入的信号分子是N-酰基-L-高丝氨酸内酯（AHLs），细菌利用它们在一个被称为“群体感应”的过程中监测自身的种群密度。这些密度依赖性调节系统依赖于两种蛋白质，一种AHL合酶，通常是LuxI家族蛋白质的成员，以及一种属于LuxR家族转录调节因子的AHL受体蛋白。在低种群密度下，细胞通过AHL合酶的活性产生基础水平的AHL。随着细胞密度的增加，AHL在生长培养基中积累。当达到临界阈值浓度时，AHL分子与其同源受体结合，进而导致AHL调节基因的诱导/抑制。迄今为止，在广泛的革兰氏阴性细菌中已经鉴定出依赖AHL的群体感应电路，它们调节各种功能，包括生物发光、质粒接合转移、生物膜形成、运动性、抗生素生物合成以及动植物病原体中毒力因子的产生。此外，AHL信号分子似乎在复杂聚集体的生态学中发挥重要作用，因为它们允许细菌种群相互作用以及与它们的真核宿主相互作用。
