Quorum Sensing (QS) system regulates gene expression in response to a change in the density of the bacterial population. Facultative pathogen Serratia proteamaculans 94 has a LuxI/LuxR type QS system consisting of regulatory protein SprR and AHL synthase SprI. Invasive activity of these bacteria appears at the stationary growth phase corresponding to a maximal density of the bacterial population in vitro. To evaluate the contribution of QS system of S. proteamaculans 94 to the regulation of invasive activity, in this work, S. proteamaculans SprI(−) mutant carrying the inactivated AHL synthase gene was used. Inactivation of the AHL synthase sprI gene resulted in a more than fourfold increase in the invasive activity of S. proteamaculans preceded by the increased adhesion of bacteria to the cell surface. This effect correlated with the increased expression of the outer membrane protein ompX gene and the decrease in the activity of intrabacterial protease protealysin, whose substrate is OmpX. The inverse correlation between activity of protealysin and bacterial invasion was also observed in the model experiments under the iron-limiting culture conditions. These results show that QS system regulates the S. proteamaculans invasion. This regulation can involve changes both in the protealysin activity and in the level of the ompX gene transcription.

群体感应 (QS) 系统调节基因表达以响应细菌种群密度的变化。兼性病原体Serratia proteamaculans 94 具有 LuxI/LuxR 型 QS 系统，由调节蛋白 SprR 和 AHL 合酶 SprI 组成。这些细菌的侵入活性出现在与体外细菌种群的最大密度相对应的静止生长期。为了评估S. proteamaculans 94 的 QS 系统对调节侵袭活性的贡献，在这项工作中，使用了携带失活 AHL 合酶基因的S. proteamaculans SprI(-) 突变体。AHL合酶sprI的失活基因导致S. proteamaculans的侵袭活性增加了四倍以上，然后细菌与细胞表面的粘附性增加。这种效应与外膜蛋白ompX基因的表达增加和细菌内蛋白酶 protealysin 的活性降低有关，其底物是 OmpX。在限铁培养条件下的模型实验中也观察到蛋白酶活性与细菌入侵之间的负相关。这些结果表明，QS 系统调节S. proteamaculans入侵。这种调节可能涉及蛋白酶活性和ompX基因转录水平的变化。