Iron limitation by transferrin promotes simultaneous cheating of pyoverdine and exoprotease in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a primary bacterial model to study cooperative behaviors because it yields exoproducts such as siderophores and exoproteases that act as public goods and can be exploited by selfish nonproducers behaving as social cheaters. Iron-limited growth medium, mainly casamino acids medium supplemented with transferrin, is typically used to isolate and study nonproducer mutants of the siderophore pyoverdine. However, using a protein as the iron chelator could inadvertently select mutants unable to produce exoproteases, since these enzymes can degrade the transferrin to facilitate iron release. Here we investigated the evolutionary dynamics of pyoverdine and exoprotease production in media in which iron was limited by using either transferrin or a cation chelating resin. We show that concomitant loss of pyoverdine and exoprotease production readily develops in media containing transferrin, whereas only pyoverdine loss emerges in medium treated with the resin. Characterization of exoprotease- and pyoverdine-less mutants revealed loss in motility, different mutations, and large genome deletions (13-33 kb) including Quorum Sensing (lasR, rsal, and lasI) and flagellar genes. Our work shows that using transferrin as an iron chelator imposes simultaneous selective pressure for the loss of pyoverdine and exoprotease production. The unintended effect of transferrin uncovered by our experiments can help to inform the design of similar studies.

The bright side of social cheaters: potential beneficial roles of "social cheaters" in microbial communities.

Cooperation in microbial communities via production of public goods is susceptible to social cheating, since selfish individuals that do not contribute to their synthesis but benefit from their production thrive in the presence of cooperators. This behavior has been observed in the laboratory using bacterial and yeast models. Moreover, growing evidence indicates that cheating is frequent in natural microbial communities. In the laboratory, social cheating can promote population collapse or "tragedy of the commons" when excessive. Nevertheless, there are diverse mechanisms that counteract cheating in microbes, as well as theoretical and experimental evidence that suggests possible beneficial roles of social cheaters for the microbial populations. In this mini review manuscript we compile and discuss such possible roles.

Rhamnolipids stabilize quorum sensing mediated cooperation in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is one of the main models to study social behaviors in bacteria since it synthesizes several exoproducts, including exoproteases and siderophores and release them to the environment. Exoproteases and siderophores are public goods that can be utilized by the individuals that produce them but also by non-producers, that are considered social cheaters. Molecularly exoprotease cheaters are mutants in regulatory genes such as lasR, and are commonly isolated from chronic infections and selected in the laboratory upon serial cultivation in media with protein as a sole carbon source. Despite that the production of exoproteases is exploitable, cooperators have also ways to restrict the growth and selection of social cheaters, for instance by producing toxic metabolites like pyocyanin. In this work, using bacterial competitions, serial cultivation and growth assays, we demonstrated that rhamnolipids which production is regulated by quorum sensing, selectively affect the growth of lasR mutants and are able to restrict social cheating, hence contributing to the maintenance of cooperation in Pseudomonas aeruginosa populations.

Seeding Public Goods Is Essential for Maintaining Cooperation in Pseudomonas aeruginosa.

Quorum sensing in Pseudomonas aeruginosa controls the production of costly public goods such as exoproteases. This cooperative behavior is susceptible to social cheating by mutants that do not invest in the exoprotease production but assimilate the amino acids and peptides derived by the hydrolysis of proteins in the extracellular media. In sequential cultures with protein as the sole carbon source, these social cheaters are readily selected and often reach equilibrium with the exoprotease producers. Nevertheless, an excess of cheaters causes the collapse of population growth. In this work, using the reference strain PA14 and a clinical isolate from a burn patient, we demonstrate that the initial amount of public goods (exoprotease) that comes with the inoculum in each sequential culture is essential for maintaining population growth and that eliminating the exoprotease in the inoculum leads to rapid population collapse. Therefore, our results suggest that sequential washes should be combined with public good inhibitors to more effectively combat P. aeruginosa infections.

AiiM Lactonase Strongly Reduces Quorum Sensing Controlled Virulence Factors in Clinical Strains of Pseudomonas aeruginosa Isolated From Burned Patients.

Pseudomonas aeruginosa is an opportunistic bacterium associated with healthcare infections in intensive care units (ICUs), ventilator-associated pneumonia (VAP), surgical site infections, and burns. This bacterium causes 75% of death in burned patients, since it can develop a persistent biofilm associated with infections, express several virulence factors, and antibiotic-resistance mechanisms. Some of these virulence factors are proteases such as elastase and alkaline protease, or toxic metabolites such as pyocyanin and is one of the few microorganisms able to produce cyanide, which inhibits the cytochrome oxidase of host cells. These virulence factors are controlled by quorum sensing (QS). In this work, 30 P. aeruginosa clinical strains isolated from burned patients from a tertiary hospital in Mexico City were studied. Antibiotic susceptibility tests were done, and virulence factors (elastase, alkaline protease, HCN, and pyocyanin) were determined in presence of an N-acylhomoserine lactonase, AiiM able to hydrolyze a wide range of acyl homoserine lactones. The treatment reduced significantly the activities of elastase and alkaline protease, and the production of pyocyanin and HCN in all producer strains but not the secretion of toxins through the type III secretion system. Our work suggests that AiiM treatment may be an effective therapy to combat P. aeruginosa infection in burn patients.

Alternativas farmacológicas para el Síndrome de Raynaud / Pharmacological alternatives in Raynaud's Syndrome

Introducción: El síndrome de Raynaud consiste en un complejo sintomático secundario a vasoespasmo vascular periférico en respuesta a un estímulo térmico frío y/o emocional, este último mediado por adrenalina.El objetivo del estudio es comparar el efecto de la nifedipina con la pentoxifilina y cinarizina en el tratamiento del vasoespasmo microvascular. Metodología: El estudio se realizó en el laboratorio de Cirugía Experimental del Instituto Guatemalteco de Seguridad Social (IGSS), en 16 ratas del laboratorio; a quines se les dió anestesia con midazolam y fentanil vía intraperitoneal, exponiéndoseles el paquete neurovascular femoral, posteriormente se les indujo vasoespasmo instilando adrenalina sobre la arteria femoral, midiendo los valores de oximetría de pulso preinducción del vasoespasmo, así como cada 5 minutos durante 30 minutos transprocedimiento. Se agruparon 4 grupos de ratas de 4 ratas cada uno, un grupo control al cual no se le dió ningún medicamento, al grupo II se le dió nifedipina (0.30 mg/kg. V.0) 30 minutos antes del procedimiento, al grupo III pentoxifilina (25 mg/kg V.O) y al grupo IV cinarizina (1 mg/kg V.0) 72 hrs. previas al procedimiento. Resultados: El grupo control presentó descenso de la saturación de 88 por ciento a 43 por ciento a los 5 minutos de inducido el vasoespasmo, manteniéndose durante 30 minutos. El grupo con nifedipina mostró una mejora en la oximetría preinduccción de vasoespasmo de 98 por ciento, diez por ciento superior del grupo control, presentando posteriormente saturación de 68 por ciento a los 5 minutos del vasoespasmo, iniciando a compensarse a los 15 minutos (72 por ciento) alcanzándose niveles de 90 por ciento a los 30 minutos. El grupo con pentoxifilina presentó una oximetría de 86 por ciento preinducción del vasoespasmo, disminuyendo la saturación a 72 por ciento a los 5 minutos de inducido el vasoespasmo, iniciando, a compensarse a los 10 minutos (76 por ciento) alcanzando su pico máximo a los 20 minutos (83 por ciento); pero con tendencia a disminuir de nuevo al final de los 30 minutos (78 por ciento) y no llegando a alcanzar su valor inicial