We describe swarming in Pseudomonas aeruginosa as a third mode of surface translocation in addition to the previously described swimming and twitching motilities. Swarming in P. aeruginosa is induced on semisolid surfaces (0.5 to 0.7% agar) under conditions of nitrogen limitation and in response to certain amino acids. Glutamate, aspartate, histidine, or proline, when provided as the sole source of nitrogen, induced swarming, while arginine, asparagine, and glutamine, among other amino acids, did not sustain swarming. Cells from the edge of the swarm were about twice as long as cells from the swarm center. In both instances, bacteria possessing two polar flagella were observed by light and electron microscopy. While a fliC mutant of P. aeruginosa displayed slightly diminished swarming, a pilR and a pilA mutant, both deficient in type IV pili, were unable to swarm. Furthermore, cells with mutations in the las cell-to-cell signaling system showed diminished swarming behavior, while rhl mutants were completely unable to swarm. Evidence is presented for rhamnolipids being the actual surfactant involved in swarming motility, which explains the involvement of the cell-to-cell signaling circuitry of P. aeruginosa in this type of surface motility.Pseudomonas aeruginosa is a gram-negative bacterium living in soil and aqueous environments, where it survives due to its extraordinary metabolic abilities. P. aeruginosa is also a typical opportunistic pathogen which colonizes the lungs of cystic fibrosis patients and causes severe infections in immunocompromised hosts. Due to its notorious elevated intrinsic resistance to antimicrobial agents and its ability to attach to and to form biofilms on medical devices (9), P. aeruginosa is difficult to eradicate in the hospital environment.P. aeruginosa has a single polar flagellum which enables the cell to swim in aqueous environments and in low-agar (Ͻ0.4%) medium. The flagellum and the chemotaxis system, consisting of chemoreceptors (11, 49) and a signal relay system similar to that of Escherichia coli (25,31), allow the bacterium to respond to attractants and repellents. In addition, P. aeruginosa is able to propagate at surface interfaces by twitching motility, which is mediated by type IV pili (5,12,53). Twitching motility is believed to result from the extension and retraction of the pilus filament, which propels the cells across a surface. Pilus synthesis and assembly require at least 40 genes which are located in several unlinked regions on the chromosome (22). The nature of the environmental signal that triggers the expression of pili is not known. Pili are important for attachment to epithelial cells (8, 17) and contribute to the virulence of P. aeruginosa in animal models (19,50,51). Furthermore, twitching motility and, hence, type IV pili are required for the formation of biofilms on abiotic surfaces (38).Besides swimming and twitching, several gram-negative bacteria are able to propagate on semisolid surfaces (i.e., 0.4 to 1.0% agar) in a coordinated manner by swarming ...

In an attempt to provide immunological tools for subfractionation of high-density lipoproteins (HDL), monoclonal antibodies were raised against HDL complexes. Two clones identified a peptide, provisionally named K-45 (PI 4.5-4.9; molecular mass 45 kDa, range 42-48 kDa), whose plasma distribution and lipoprotein association were fully characterised. Gel filtration localised the peptide to the HDL region of human plasma where it co-eluted with apolipoprotein (apo) A-I, the structural protein of HDL. Complementary studies employing immunoabsorption with anti-(apo A-I) antibodies removed 90 % of K-45 from plasma: conversely, anti-(apo A-11) antibodies eliminated only 10 % of K-45. Immunoaffinity chromatography on an anti-(K-45) column revealed that the peptide was present in a distinct HDL subspecies containing three major proteins: K-45, apo A-I and clusterin or apo J. The lipoprotein nature of the bound fraction was indicated by electron microscopy (diameter 9.6 ? 3.3 nm) and quantification of lipids, the latter showing an unusually high triacyglycerol concentration. Plasma concentrations of K-45 were positively correlated with apo A-I and HDL-cholesterol and negatively correlated with apo B and total cholesterol. Thus, the peptide appears to be linked, directly or indirectly, to processes which give rise to an anti-atherogenic lipid profile. After completion of the present studies, an N-terminal sequence identical to that of K-45 was reported in recently isolated cDNA clones. These clones encode paraoxonase.Lipoprotein complexes are the principal transport vehicles for plasma lipids. As such, they are the focus of particular attention which derives from the designation of blood lipids as primary cardiovascular risk factors [l, 21. The rationale behind these studies is that a dysfunctional lipid transport system will be a major cause of the dyslipidaemias associated with premature cardiovascular disease [3]. In this context, an obvious pre-requisite is a comprehensive understanding of the normal functioning of the lipoprotein metabolic system ; unfortunately, this is not currently the case. It is due, in part, to the highly dynamic nature of this metabolic process, rendered even more intricate by extensive interactions between the major subclasses, very-low-density (VLDL), low-density (LDL) and high-density (HDL) lipoproteins [4]. The latter are of particular interest as they afford a measure of protection against cardiovascular disease [5, 61. Yet many aspects of HDL metabolism are poorly understood. Neither the origins nor the sites of catabolism of this lipoprotein species have been convincingly demonstrated. Additionally, the mechanisms by which HDL assure their postuCorrespondence to R.

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Summary Iron and zinc are necessary nutrients whose homeostasis is tightly controlled by members of the ferric uptake regulator (FUR) superfamily in the cyanobacterium Anabaena sp. PCC7120. Although the link between iron metabolism and oxidative stress management is well documented, little is known about the connection between zinc homeostasis and the oxidative stress response in cyanobacteria. Zinc homeostasis in Anabaena is controlled by Zur, also named FurB. When overexpressed in Escherichia coli, Zur (FurB) improved cell survival during oxidative stress. In order to investigate the possible correlation between Zur and the oxidative stress response in Anabaena, zur deletion and zur‐overexpressing strains have been constructed, and the consequences of Zur imbalance evaluated. The lack of Zur increased sensitivity to hydrogen peroxide (H2O2), whereas an excess of Zur enhanced oxidative stress resistance. Both mutants displayed pleiotropic phenotypes, including alterations on the filament surfaces observable by scanning electron microscopy, reduced content of endogenous H2O2 and altered expression of sodA, catalases and several peroxiredoxins. Transcriptional and biochemical analyses unveiled that the appropriate level of Zur is required for proper control of the oxidative stress response and allowed us to identify major antioxidant enzymes as novel members of the Zur regulon.