The opportunistic pathogen Pseudomonas aeruginosa damages hosts through the production of diverse secreted products, many of which are regulated by quorum sensing (QS). The lasR gene, which encodes a central QS regulator, is frequently mutated in clinical isolates from chronic infections, and loss of LasR function (LasR−) generally impairs the activity of downstream QS regulators RhlR and PqsR. We found that in cocultures containing LasR+ and LasR− strains, LasR− strains hyperproduce the RhlR/RhlI-regulated antagonistic factors pyocyanin and rhamnolipids in diverse models and media and in different strain backgrounds. Diffusible QS autoinducers produced by the wild type were not required for this effect. Using transcriptomics, genetics, and biochemical approaches, we uncovered a reciprocal interaction between wild-type and lasR mutant pairs wherein the iron-scavenging siderophore pyochelin produced by the lasR mutant induced citrate release and cross-feeding from the wild type. Citrate, a metabolite often secreted in low iron environments, stimulated RhlR signaling and RhlI levels in LasR−but not in LasR+ strains. These studies reveal the potential for complex interactions between recently diverged, genetically distinct isolates within populations from single chronic infections. IMPORTANCE Coculture interactions between lasR loss-of-function and LasR+ Pseudomonas aeruginosa strains may explain the worse outcomes associated with the presence of LasR− strains. More broadly, this report illustrates how interactions within a genotypically diverse population, similar to those that frequently develop in natural settings, can promote unpredictably high virulence factor production.

Much of the difficulty encountered in the chromatographic separation of members of polymeric series is due to the inability of the larger molecules to enter the porous materials used for chromatography. Electrokinetic ultrafiltration was proposed to circumvent this.A preliminary account is now given of experiments with collodion ultrafiltration membranes, where this principle gave useful separations of a series of enzyme-synthesized straight-chain polysaccharides. The data suggest that each membrane excludes molecules exceeding a certain length and that molecules penetrating a membrane undergo simple adsorption on its internal surfaces. =SUM&Parmi les difficult& dans la separation chromatographique de membres de dries polymhres l'impuissance de grandes mol6cules d'entrer dans les matihres poreuses, employbes en chromatographie, joue un rdle important. L'ultrafiltration blectrocin6tique a 6t6 proposke pour surmonter cette difficult& Nous prdsentons ici un rapport preliminaire d 'exp6riences avec des membranes de collodion pour ultrafiltration, ou ce principe donnait des ¶tions avantageuses d'une s6rie de polysaccharides de chaine linbaire, synth6tisbs par des enzymes. Les rksultats font supposer que chaque membrane exclut les molbcules excedant une certaine longueur et que les mol6cules pknktrant une membrane subissent une adsorption simple sur les surfaces internes de la membrane. ZUSAMMENFASSUNGEine der Hauptschwierigkeiten bei der chromatographischen Trennung von Gliedern polymerer Reihen liegt in der Unfahigkeit der grosseren Molekule in die porosen Materialien, wie sie fur Chromatographie venvendet werden, einzudringen. Die elektrokinetische Ultrafiltration wurde zu deren Uberwindung vorgeschlagen.Ein vorlaufiger Bericht iiber Untersuchungen mit Kollodium-Ultrafiltrationsmembranen wird hier gegeben, wobei dieses Prinzip brauchbare Trennungen einer Reihe geradkettiger Polysaccharide, die durch enzymatische Synthese erhalten.worden waren, gab. Die Resultate geben zu der Vermutung Anlass, dass j ede Membran Molekiile, die eine gewisse Lange uberschreiten, aufhalt, und dass Molekiile, die eine Membran durchdringen, einfache Adsorption an deren inneren Oberflachen erfahren.

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Pseudomonas aeruginosa frequently resides among ethanol-producing microbes, making its response to the microbially produced concentrations of ethanol relevant to understanding its biology. Our transcriptome analysis found that genes involved in trehalose metabolism were induced by low concentrations of ethanol, and biochemical assays showed that levels of intracellular trehalose increased significantly upon growth with ethanol. The increase in trehalose was dependent on the TreYZ pathway but not other trehalose-metabolic enzymes (TreS or TreA). The sigma factor AlgU (AlgT), a homolog of RpoE in other species, was required for increased expression of the treZ gene and trehalose levels, but induction was not controlled by the well-characterized proteolysis of its anti-sigma factor, MucA. Growth with ethanol led to increased SpoT-dependent (p)ppGpp accumulation, which stimulates AlgU-dependent transcription of treZ and other AlgU-regulated genes through DksA, a (p)ppGpp and RNA polymerase binding protein. Ethanol stimulation of trehalose also required acylhomoserine lactone (AHL)-mediated quorum sensing (QS), as induction was not observed in a ΔlasR ΔrhlR strain. A network analysis using a model, eADAGE, built from publicly available P. aeruginosa transcriptome data sets (J. Tan, G. Doing, K. A. Lewis, C. E. Price, et al., Cell Syst 5:63–71, 2017, https://doi.org/10.1016/j.cels.2017.06.003) provided strong support for our model in which treZ and coregulated genes are controlled by both AlgU- and AHL-mediated QS. Consistent with (p)ppGpp- and AHL-mediated quorum-sensing regulation, ethanol, even when added at the time of culture inoculation, stimulated treZ transcript levels and trehalose production in cells from post-exponential-phase cultures but not in cells from exponential-phase cultures. These data highlight the integration of growth and cell density cues in the P. aeruginosa transcriptional response to ethanol. IMPORTANCE Pseudomonas aeruginosa is often found with bacteria and fungi that produce fermentation products, including ethanol. At concentrations similar to those produced by environmental microbes, we found that ethanol stimulated expression of trehalose-biosynthetic genes and cellular levels of trehalose, a disaccharide that protects against environmental stresses. The induction of trehalose by ethanol required the alternative sigma factor AlgU through DksA- and SpoT-dependent (p)ppGpp. Trehalose accumulation also required AHL quorum sensing and occurred only in post-exponential-phase cultures. This work highlights how cells integrate cell density and growth cues in their responses to products made by other microbes and reveals a new role for (p)ppGpp in the regulation of AlgU activity.

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