A Novel Signaling Network Essential for Regulating Pseudomonas aeruginosa Biofilm Development

The important human pathogen Pseudomonas aeruginosa has been linked to numerous biofilm-related chronic infections. Here, we demonstrate that biofilm formation following the transition to the surface attached lifestyle is regulated by three previously undescribed two-component systems: BfiSR (PA4196-4197) harboring an RpoD-like domain, an OmpR-like BfmSR (PA4101-4102), and MifSR (PA5511-5512) belonging to the family of NtrC-like transcriptional regulators. These two-component systems become sequentially phosphorylated during biofilm formation. Inactivation of bfiS, bfmR, and mifR arrested biofilm formation at the transition to the irreversible attachment, maturation-1 and -2 stages, respectively, as indicated by analyses of biofilm architecture, and protein and phosphoprotein patterns. Moreover, discontinuation of bfiS, bfmR, and mifR expression in established biofilms resulted in the collapse of biofilms to an earlier developmental stage, indicating a requirement for these regulatory systems for the development and maintenance of normal biofilm architecture. Interestingly, inactivation did not affect planktonic growth, motility, polysaccharide production, or initial attachment. Further, we demonstrate the interdependency of this two-component systems network with GacS (PA0928), which was found to play a dual role in biofilm formation. This work describes a novel signal transduction network regulating committed biofilm developmental steps following attachment, in which phosphorelays and two sigma factor-dependent response regulators appear to be key components of the regulatory machinery that coordinates gene expression during P. aeruginosa biofilm development in response to environmental cues

Measurement of the e(+)e(-)->gamma gamma(gamma) cross section at the LEP energies

The total and the differential cross-sections for the reaction e(+)e(-) –> gamma gamma(gamma) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb(-1). The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z(0) energies) on the QED cutoff parameters are Lambda(+) > 253 GeV and Lambda(-) > 225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant lambda(gamma) = 1 is 231 GeV/c(2). All the Limits are at the 95% confidence level. (C) 1998 Published by Elsevier Science B.V. All rights reserved