Burkholderia pseudomallei is the causative agent of melioidosis, an often fatal infection of humans and animals. The virulence of this pathogen is thought to depend on a number of secreted proteins, including the MprA metalloprotease. We observed that MprA is produced upon entry into the stationary phase, when the cell density is high, and this prompted us to study cell density-dependent regulation in B. pseudomallei. A search of the B. pseudomallei genome led to identification of a quorum-sensing system involving the LuxI-LuxR homologs PmlI-PmlR. PmlI directed the synthesis of an N-acylhomoserine lactone identified as N-decanoylhomoserine lactone. A B. pseudomallei pmlI mutant was significantly less virulent than the parental strain in a murine model of infection by the intraperitoneal, subcutaneous, and intranasal routes. Inactivation of pmlI resulted in overproduction of MprA at the onset of the stationary phase. A wild-type phenotype was restored following complementation with pmlI or addition of cell-free culture supernatant. In contrast, there was no significant difference between the virulence of a B. pseudomallei mprA mutant and the virulence of the wild-type strain. These results suggest that the PmlI-PmlR quorum-sensing system of B. pseudomallei is essential for full virulence in a mouse model and downregulates the production of MprA at a high cell density.

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Surface energy is very important concept in the materials science and engineering. For solids, this can be calculated from contact angle measurements and different theoretical approximations; however, when a membrane is the object of study, porosity can be considered to be the main factor affecting the measures of contact angle and, in consequence, the results of surface energy. The objectives of this article is the performing of the theoretical description for the determination of surface energy from contact angle measures and to give key points for physical interpretation of data and illustrate its application for characterization of polymeric materials.

En el contexto de la fertilización de cultivos con ácido bórico (H3BO3), la utilización de materiales con capacidad de carga (retención de boro) y descarga (liberación del boro retenido), tienen potenciales aplicaciones en el desarrollo de sistemas de fertilización y en el tratamiento de aguas de riego. En el presente estudio se planteó obtener un material compuesto, basado en poliuretanos (PUs) y N-(4-vinilbencil)-N-metil-D-glucamina (VbNMDG), mediante la técnica de redes poliméricas interpenetrantes (RPIs), con potenciales aplicaciones en el desarrollo de sistemas de fertilización de boro. Para ello, diferentes matrices de PU fueron sintetizadas a partir de un isocianato (metilendifenil-isocianato, MDI) y polioles de peso molecular variable (etilenglicol, glicerol, manitol). Estos PUs fueron empleados como matriz soporte de una segunda red polimérica sintetizada a partir de la polimerización por radicales libres del VbNMDG, el cual fue sintetizado mediante sustitución nucleofílica entre el p-clorometilestireno (ClME) y la N-metil-D-glucamina (NMDG). La capacidad de retención y liberación de boro se evaluó mediante experimentos tipo batch realizándose la cuantifiación del boro remanente se hizo por el método de la azometina-H. Los resultados sugieren que las RPIs preparadas a partir de manitol poseen una mayor capacidad de retención de H3BO3 respecto a las obtenidas con etilenglicol y glicerol. Las propiedades de retención de las RPIs aumentan con el aumento de la relación R–OH/H3BO3. Se concluyó que RPIs pueden ser obtenidas a partir de PUs y poli(VbNMDG) empleando dioxano como solvente

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Mid-infrared spectroscopy in conjunction with Functionally-Enhanced Derivative Spectroscopy (IR+FEDS) is a powerful analytical tool for the improvement of analysis of microorganism IR spectra. The objective of this research is to characterize the outer surface of two Helicobacter pylori strains by IR+FEDS. This work is a key stage for the study of cell-cell and cell-surface interactions between microorganisms, as well as, for polymicrobial biofilm characterizations where H. pylori species are involved. Artificial bacterial biofilms were deposited on ultrafiltration cellulose membranes covalently modified by insertion of one spectral marker and used as sensing surface for analysis of bacterial biolayers. Biolayers were analyzed using an infrared spectrophotometer with ATR. Data were analyzed by classic procedures and by deconvolution based on FEDS transform. It is concluded that, for correct application of technique is required a minimum amount of noise in the working spectra which can be achieved by simple smoothing algorithms; in addition, reproducibility must be warranted by the implementation of standardized protocols and the use of an appropriate number of samples. It is concluded that in addition to typical signals associated with the IR spectrum of microorganisms, by FEDS, a better and more detailed description of the outer membrane of H. pylori biofilms can be performed. In particular, it is concluded that the detecting and monitoring of cysteine-rich proteins can be satisfactorily performed by IR+FEDS.