A natural isolate of Pseudomonas maltophila which degrades aromatic sulfonic acids

Abstract A natural isolate, designated BSA56, which was originally selected for growth with benzene sulfuric acid as sole carbon and energy source, was identified as a strain of Pseudomonas maltophila . Strain BSA56 grew on a wide range of aromatic sulfonic acids and was shown to release sulfite from benzene sulfonic acid and 2-napthalene sulforic acid. Although it also grew on toluene sulfonic acid and pyridine sulfonic acid, no significant sulfite release was observed with these substrates. Release of sulfite from benzene sulfonic acid was greatly promoted by the presence of glycerol. The ability to release sulfite was induced by growth in the presence of benzene sulfonic acid and was repressed almost entirely by substrates allowing rapid growth such as acetate. Strain BSA56 grew better at 30°C than 37°C on most aromatic substrates, but the reverse was true for most aromatic sulfonates. Several mutants of BSA56 were isolated with defects in benzoate, salicylate, or gentisate metabolism. However, all these mutants retained the ability to degrade the aromatic sulfonates.     

Channel-forming properties and structural homology of major outer membrane proteins from Pseudomonas fluorescens MFO and OE 28.3

Abstract The major outer membrane proteins (OprF) from Pseudomonas fluorescens MFO and OE 28.3 were purified by a new method involving native electrophoresis in octyl-polyoxyethylene media. Both proteins, characterized by the same size, heat-modifiability and N-terminal sequence were re-incorporated in virtually solvent-free planar lipid bilayers. They displayed very similar channel-forming properties: the major conductance level was between 250 pS and 270 pS in l M NaCl. From experiments of zero-current potential, both porins were determined weakly cation selective. Amplification by PCR and sequencing of the oprF gene of strain MFO allowed to point out 94% identity between the amino acid sequences of these two OprFs isolated from ecological niches as different as milk (strain MFO) and soil (strain OE 28.3).     

Interaction between hyaluronate and the cell surface of Pseudomonas aeruginosa

Abstract Treatment of Pseudomonas aeruginosa cells with the non-metabolizable polysaccharide hyaluronate led to a strong increase in extracellular lipase activity. Alteration of the cell surface either by treatment with the chelator EDTA or by selecting for phage-resistant mutants significantly altered the bacterial response to hyaluronate. Binding of ¹⁴C-labeled hyaluronate to the bacteria was shown to depend on polysaccharide concentration and on cell number. Cell-free exolipase interacted with chemically cross-linked hyaluronate. The results suggested an interaction between hyaluronate and the cell surface of P. aeruginosa as a prerequisite for the polysaccharide to be effective.     

Biological activity of Burkholderia (Pseudomonas) cepacia lipopolysaccharide

Abstract Burkholderia cepacia has emerged as an important multiresistant pathogen in cystic fibrosis (CF), associated in 20% of colonised patients with a rapid and fatal decline in lung function. Although knowledge of B. cepacia epidemiology has improved, the mechanisms involved in pathogenesis remain obscure. In this study, B. cepacia lipopolysaccharide (LPS) was assessed for endotoxic potential and the capacity to induce tumour necrosis factor (TNF). LPS preparations from clinical and environmental isolates of B. cepacia and from the closely related species Burkholderia gladioli exhibited a higher endotoxic activity and more pronounced cytokine response in vitro compared to preparations from the major CF pathogen Pseudomonas aeruginosa . This study may help to explain the vicious host immune response observed during pulmonary exacerbations in CF patients colonised by B. cepacia and lead to therapeutic advances in clinical management.     

V‐antigen homologs in pathogenic gram‐negative bacteria

Gram‐negative bacteria cause many types of infections in animals from fish and shrimps to humans. Bacteria use Type III secretion systems (TTSSs) to translocate their toxins directly into eukaryotic cells. The V‐antigen is a multifunctional protein required for the TTSS in Yersinia and Pseudomonas aeruginosa. V‐antigen vaccines and anti‐V‐antigen antisera confer protection against Yersinia or P. aeruginosa infections in animal models. The V‐antigen forms a pentameric cap structure at the tip of the Type III secretory needle; this structure, which has evolved from the bacterial flagellar cap structure, is indispensable for toxin translocation. Various pathogenic gram‐negative bacteria such as Photorhabdus luminescens, Vibrio spp., and Aeromonas spp. encode homologs of the V‐antigen. Because the V‐antigens of pathogenic gram‐negative bacteria play a key role in toxin translocation, they are potential therapeutic targets for combatting bacterial virulence. In the USA and Europe, these vaccines and specific antibodies against V‐antigens are in clinical trials investigating the treatment of Yersinia or P. aeruginosa infections. Pathogenic gram‐negative bacteria are of great interest because of their ability to infect fish and shrimp farms, their potential for exploitation in biological terrorism attacks, and their ability to cause opportunistic infections in humans. Thus, elucidation of the roles of the V‐antigen in the TTSS and mechanisms by which these functions can be blocked is critical to facilitating the development of improved anti‐V‐antigen strategies.     

Inactivation of Salmonella serovars by Pseudomonas chlororaphis and Pseudomonas fluorescens strains on tomatoes

Salmonella enterica and its serovars have been associated with pathogen contamination of tomatoes with numerous outbreaks of salmonellosis. To improve food safety, pathogen control is of immediate concern. The aim of this research was to assess the populations of natural microflora (aerobic mesophilic bacteria, lactic acid bacteria, yeasts and moulds and Pseudomonas species) on tomatoes, and evaluate the efficacy of Pseudomonas fluorescens (Pf) and Pseudomonas chlororaphis (Pc) for inactivation of Salmonella on tomatoes. Microflora were determined on sanitised and unsanitised produce and enumerated on Plate Count Agar, de Man, Rogosa and Sharpe medium, Potato Dextrose Agar and Pseudomonas Agar F media. The efficacy of Pc and Pf for inactivation of S. enterica serovars Montevideo, Typhimurium and Poona was determined on spot-inoculated tomato stem scars. The effects of storage time on bacterial populations were also investigated. On unsanitised tomatoes, lactic acid bacteria, Pseudomonas sp., aerobic mesophilic bacteria and yeasts and moulds ranged from 3.31–4.84, 3.93–4.77, 4.09–4.80 and 3.83–4.67 log CFU/g of produce, respectively. The microflora were similar at 0 and 24 storage hours on sanitised produce. The suppression of Salmonella Montevideo by P. chlororaphis and P. fluorescens on tomatoes ranged from 0.51 to 2.00 log CFU/g of produce. On Salmonella Montevideo and S. Typhimurium, the suppressive effects ranged from 0.51 to 0.95 and 0.46 to 2.00 log CFU/g of produce, respectively. The pathogen suppressive effects may be attributed to competition ability of Pseudomonas relative to Salmonella strains. Pseudomonas strains may be effective against Salmonella strains as a post-harvest application, but strain synergy is required to optimise pathogen reductions.