假单胞菌株M18中pqsA突变株的构建及其对plt的调控

【目的】根际铜绿假单胞菌M18能产生藤黄绿菌素(Plt)和吩嗪-1-羧酸(PCA)两种主要的抗生素。其PqsR/PQS群体感应系统由应答调控蛋白PqsR与信号分子PQS组成。前期研究已经表明pqsR负调控Plt生物合成及基因簇表达。本论文旨在研究PQS分子对Plt合成及基因表达的调控作用。【方法】从M18基因组中扩增PQS合成基因pqsA,通过同源重组技术构建假单胞菌M18的pqsA突变菌株M18pqsA。利用lacZ报告基因分析、信号分子添加实验等,研究PQS对Plt合成及基因表达的调控作用。【结果】在KMB培养基中,分别比较野生型菌株M18和突变菌株M18pqsA的Plt产量,突变菌株的Plt产量存在较小幅度的升高,约为野生型菌株的1.53倍。添加PQS对plt表达存在一定程度但不是很显著的负调控作用。【结论】PQS分子对Plt生物合成及基因表达存在部分负调控作用。     

A dual biosensor for 2-alkyl-4-quinolone quorum-sensing signal molecules

Pseudomonas, Burkholderia and Alteromonas species produce diverse 2-alkyl-4-quinolones (AHQs) which inhibit the growth of bacteria, algae and phytoplankton, chelate iron, modulate mammalian host immune defences and act as quorum-sensing (QS) signal molecules. To facilitate the detection, identification and quantification of the major Pseudomonas aeruginosa AHQs 2-heptyl-3-hydroxy-4-quinolone (PQS) and 2-heptyl-4-quinolone (HHQ) we developed two different AHQ biosensors. These were constructed by introducing either a lecA::luxCDABE or a pqsA::luxCDABE reporter gene fusion into a P. aeruginosa pqsA mutant which cannot synthesize AHQs. While both biosensors responded similarly to PQS (EC(50) 18 +/- 4 microM), the pqsA::luxCDABE biosensor was most sensitively activated by HHQ (EC(50) 0.44 +/- 0.1 microM). This biosensor was also activated albeit less sensitively by (i) PQS analogues with alkyl chains varying from C1 to C11, (ii) HHQ analogues with C9 and C11 alkyl chains and (iii) 2-heptyl-4-hydroxyquinoline-N-oxide (HHQNO). The AHQ biosensor also responded differentially to the AHQs present in cell free culture supernatants prepared from PAO1 and isogenic strains carrying mutations in genes (pqsA, pqsH, lasR, lasI, rhlR, rhlI) known to influence AHQ production. The AHQ profiles of P. aeruginosa strains was also evaluated by overlaying thin layer chromatogram (TLC) plates with the pqsA::luxCDABE biosensor. In PAO1, three major bioluminescent spots were observed which correspond to PQS, HHQ and a mixture of 2 nonyl-4-quinolone and HHQNO. We also noted that on TLC plates the biosensor not only produced bioluminescence in response to AHQs but also the green pigment, pyocyanin which offers an alternative visual indicator for AHQ production.     

Identification of Small-Molecule Antagonists of the Pseudomonas aeruginosa Transcriptional Regulator PqsR: Biophysically Guided Hit Discovery and Optimization

The Gram-negative pathogen Pseudomonas aeruginosa produces an intercellular alkyl quinolone signaling molecule, the Pseudomonas quinolone signal. The pqs quorum sensing communication system that is characteristic for P. aeruginosa regulates the production of virulence factors. Therefore, we consider the pqs system a novel target to limit P. aeruginosa pathogenicity. Here, we present small molecules targeting a key player of the pqs system, PqsR. A rational design strategy in combination with surface plasmon resonance biosensor analysis led to the identification of PqsR binders. Determination of thermodynamic binding signatures and functional characterization in E. coli guided the hit optimization, resulting in the potent hydroxamic acid derived PqsR antagonist 11 (IC(50) = 12.5 μM). Remarkably it displayed a comparable potency in P. aeruginosa (IC(50) = 23.6 μM) and reduced the production of the virulence factor pyocyanin. Beyond this, site-directed mutagenesis together with thermodynamic analysis provided insights into the energetic characteristics of protein-ligand interactions. Thus the identified PqsR antagonists are promising scaffolds for further drug design efforts against this important pathogen.     

Influence of the Pseudomonas quinolone signal on denitrification in Pseudomonas aeruginosa

Denitrification is a well-studied respiratory system that is also important in the biogeochemical nitrogen cycle. Environmental signals such as oxygen and N-oxides have been demonstrated to regulate denitrification, though how denitrification is regulated in a bacterial community remains obscure. Pseudomonas aeruginosa is a ubiquitous bacterium that controls numerous genes through cell-to-cell signals. The bacterium possesses at least two N-acyl-L-homoserine lactone (AHL) signals. In our previous study, these quorum-sensing signals controlled denitrification in P. aeruginosa. In addition to the AHL signals, a third cell-to-cell communication signal, 2-heptyl-3-hydroxy-4-quinolone, referred to as the Pseudomonas quinolone signal (PQS), has been characterized. In this study, we examined the effect of PQS on denitrification to obtain more insight into the respiratory regulation in a bacterial community. Denitrification in P. aeruginosa was repressed by PQS, which was partially mediated by PqsR and PqsE. Measuring the denitrifying enzyme activities indicated that nitrite reductase activity was increased by PQS, whereas PQS inhibited nitric oxide reductase and the nitrate-respiratory chain activities. This is the first report to demonstrate that PQS influences enzyme activities, suggesting this effect is not specific to P. aeruginosa. Furthermore, when iron was supplied to the PQS-added medium, denitrifying activity was almost restored, indicating that the iron chelating property of PQS affected denitrification. Thus, our data indicate that PQS regulates denitrification primarily through iron chelation. The PQS effect on denitrification was relevant in a condition where oxygen was limited and denitrification was induced, suggesting its role in controlling denitrification where oxygen is present.     

The YebC family protein PA0964 negatively regulates the Pseudomonas aeruginosa quinolone signal system and pyocyanin production

Bacterial pathogenicity is often manifested by the expression of various cell-associated and secreted virulence factors, such as exoenzymes, protease, and toxins. In Pseudomonas aeruginosa, the expression of virulence genes is coordinately controlled by the global regulatory quorum-sensing systems, which includes the las and rhl systems as well as the Pseudomonas quinolone signal (PQS) system. Phenazine compounds are among the virulence factors under the control of both the rhl and PQS systems. In this study, regulation of the phzA1B1C1D1E1 (phzA1) operon, which is involved in phenazine synthesis, was investigated. In an initial study of inducing conditions, we observed that phzA1 was induced by subinhibitory concentrations of tetracycline. Screening of 13,000 mutants revealed 32 genes that altered phzA1 expression in the presence of subinhibitory tetracycline concentrations. Among them, the gene PA0964, designated pmpR (pqsR-mediated PQS regulator), has been identified as a novel regulator of the PQS system. It belongs to a large group of widespread conserved hypothetical proteins with unknown function, the YebC protein family (Pfam family DUF28). It negatively regulates the quorum-sensing response regulator pqsR of the PQS system by binding at its promoter region. Alongside phzA1 expression and phenazine and pyocyanin production, a set of virulence factors genes controlled by both rhl and the PQS were shown to be modulated by PmpR. Swarming motility and biofilm formation were also significantly affected. The results added another layer of regulation in the rather complex quorum-sensing systems in P. aeruginosa and demonstrated a clear functional clue for the YebC family proteins.     

The influence of iron on Pseudomonas aeruginosa physiology: a regulatory link between iron and quorum sensing

In iron-replete environments, the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein represses expression of two small regulatory RNAs encoded by prrF1 and prrF2. Here we describe the effects of iron and PrrF regulation on P. aeruginosa physiology. We show that PrrF represses genes encoding enzymes for the degradation of anthranilate (i.e. antABC), a precursor of the Pseudomonas quinolone signal (PQS). Under iron-limiting conditions, PQS production was greatly decreased in a DeltaprrF1,2 mutant as compared with wild type. The addition of anthranilate to the growth medium restored PQS production to the DeltaprrF1,2 mutant, indicating that its defect in PQS production is a consequence of anthranilate degradation. PA2511 was shown to encode an anthranilate-dependent activator of the ant genes and was subsequently renamed antR. AntR was not required for regulation of antA by PrrF but was required for optimal iron activation of antA. Furthermore, iron was capable of activating both antA and antR in a DeltaprrF1,2 mutant, indicating the presence of two distinct yet overlapping pathways for iron activation of antA (AntR-dependent and PrrF-dependent). Additionally, several quorum-sensing regulators, including PqsR, influenced antA expression, demonstrating that regulation of anthranilate metabolism is intimately woven into the quorum-sensing network of P. aeruginosa. Overall, our data illustrate the extensive control that both iron regulation and quorum sensing exercise in basic cellular physiology, underlining how intermediary metabolism can affect the regulation of virulence factors in P. aeruginosa.     

Quorum sensing by 2-alkyl-4-quinolones in Pseudomonas aeruginosa and other bacterial species

Pseudomonas aeruginosa produces the cell-to-cell signal molecule 2-heptyl-3-hydroxy-4-quinolone (The Pseudomonas quinolone signal; PQS), which is integrated within a complicated quorum sensing signaling system. PQS belongs to the family of 2-alkyl-4-quinolones (AQs), which have been previously described for their antimicrobial activities. PQS is synthesized via the pqsABCDE operon which is responsible for generating multiple AQs including 2-heptyl-4-quinolone (HHQ), the immediate PQS precursor. In addition, PQS signaling plays an important role in P. aeruginosa pathogenesis because it regulates the production of diverse virulence factors including elastase, pyocyanin and LecA lectin in addition to affecting biofilm formation. Here, we summarize the most recent findings on the biosynthesis and regulation of PQS and other AQs including the discovery of AQs in other bacterial species.     

Pseudomonas aeruginosa Inhibits the Growth of Cryptococcus Species

Pseudomonas aeruginosa is a ubiquitous and opportunistic bacterium that inhibits the growth of different microorganisms, including Gram-positive bacteria and fungi such as Candida spp. and Aspergillus fumigatus. In this study, we investigated the interaction between P. aeruginosa and Cryptococcus spp. We found that P. aeruginosa PA14 and, to a lesser extent, PAO1 significantly inhibited the growth of Cryptococcus spp. The inhibition of growth was observed on solid medium by the visualization of a zone of inhibition of yeast growth and in liquid culture by viable cell counting. Interestingly, such inhibition was only observed when P. aeruginosa and Cryptococcus were co-cultured. Minimal inhibition was observed when cell-cell contact was prevented using a separation membrane, suggesting that cell contact is required for inhibition. Using mutant strains of Pseudomonas quinoline signaling, we showed that P. aeruginosa inhibited the growth of Cryptococcus spp. by producing antifungal molecules pyocyanin, a redox-active phenazine, and 2-heptyl-3,4-dihydroxyquinoline (PQS), an extracellular quorum-sensing signal. Because both P. aeruginosa and Cryptococcus neoformans are commonly found in lung infections of immunocompromised patients, this study may have important implication for the interaction of these microbes in both an ecological and a clinical point of view.