Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA.
J Bacteriol. 2013 Jul;195(13):2971-81. doi: 10.1128/JB.02267-12. Epub 2013 Apr 26.
As an opportunistic Gram-negative pathogen, Pseudomonas aeruginosa must be able to adapt and survive changes and stressors in its environment during the course of infection. To aid survival in the hostile host environment, P. aeruginosa has evolved defense mechanisms, including the production of an exopolysaccharide capsule and the secretion of a myriad of degradative proteases and lipases. The production of outer membrane-derived vesicles (OMVs) serves as a secretion mechanism for virulence factors as well as a general bacterial response to envelope-acting stressors. This study investigated the effect of sublethal physiological stressors on OMV production by P. aeruginosa and whether the Pseudomonas quinolone signal (PQS) and the MucD periplasmic protease are critical mechanistic factors in this response. Exposure to some environmental stressors was determined to increase the level of OMV production as well as the activity of AlgU, the sigma factor that controls MucD expression. Overexpression of AlgU was shown to be sufficient to induce OMV production; however, stress-induced OMV production was not dependent on activation of AlgU, since stress caused increased vesiculation in strains lacking algU. We further determined that MucD levels were not an indicator of OMV production under acute stress, and PQS was not required for OMV production under stress or unstressed conditions. Finally, an investigation of the response of P. aeruginosa to oxidative stress revealed that peroxide-induced OMV production requires the presence of B-band but not A-band lipopolysaccharide. Together, these results demonstrate that distinct mechanisms exist for stress-induced OMV production in P. aeruginosa.
作为一种机会性革兰氏阴性病原体，铜绿假单胞菌在感染过程中必须能够适应和应对其环境中的变化和应激源。为了帮助在宿主环境中生存，铜绿假单胞菌已经进化出防御机制，包括产生外多糖荚膜和分泌大量降解蛋白酶和脂肪酶。外膜衍生小泡（OMVs）的产生既是毒力因子的分泌机制，也是细菌对膜作用应激源的一般反应机制。本研究调查了亚致死生理应激源对铜绿假单胞菌 OMV 产生的影响，以及假单胞菌喹诺酮信号（PQS）和 MucD 周质蛋白酶是否是这种反应的关键机制因素。暴露于某些环境应激源会增加 OMV 的产生水平以及控制 MucD 表达的 sigma 因子 AlgU 的活性。结果表明，过表达 AlgU 足以诱导 OMV 的产生；然而，应激诱导的 OMV 产生并不依赖于 AlgU 的激活，因为应激导致 algU 缺失菌株中囊泡的增加。我们进一步确定，在急性应激下，MucD 水平不是 OMV 产生的指标，PQS 不是应激或非应激条件下 OMV 产生所必需的。最后，对铜绿假单胞菌对氧化应激的反应进行了研究，结果表明过氧化物诱导的 OMV 产生需要 B 带而不是 A 带脂多糖的存在。总之，这些结果表明铜绿假单胞菌中存在应激诱导 OMV 产生的不同机制。
