|
|
|
|
|
|
Escherichia coli Serogroup O107/O117 Lipopolysaccharide Binds and Neutralizes Shiga Toxin 2. Shantini D. Gamage, 2004.The AB5 toxin Shiga toxin 2 (Stx2) has been implicated as a major virulence factor of Escherichia coli O157:H7 and other Shiga toxin-producing E . coli strains in the progression of intestinal disease to more severe systemic complications . Here, we demonstrate that supernatant from a normal E . coli isolate, FI-29, neutralizes the effect of Stx2, but not the related Stx1, on Vero cells . Biochemical characterization of the neutralizing activity identified the lipopolysaccharide (LPS) of FI-29, a serogroup O107/O117 strain, as the toxin-neutralizing component . LPSs from FI-29 as well as from type strains E . coli O107 and E . coli O117 were able bind Stx2 but not Stx1, indicating that the mechanism of toxin neutralization may involve inhibition of the interaction between Stx2 and the Gb3 receptor on Vero cells . Characterization of a Eukaryotic-Like Tyrosine Protein Kinase Expressed by the Shiga Toxin-Encoding Bacteriophage 933W. Jessica S. Tyler, 2004.The Shiga toxin (Stx)-encoding bacteriophage 933W contains an open reading frame, stk, with amino acid sequence similarity to the catalytic domain of eukaryotic serine/threonine (Ser/Thr) protein kinases (PKs) . Eukaryotic PKs are related by a common catalytic domain, consisting of invariant and nearly invariant residues necessary for ATP binding and phosphotransfer . We demonstrate that rather than a Ser/Thr kinase, stk encodes a eukaryotic-like tyrosine (Tyr) kinase . An affinity-purified recombinant Stk (rStk) autophosphorylates and catalyzes the phosphorylation of an artificial substrate on Tyr residues and not on Ser or Thr residues . A change of an invariant lysine within the putative catalytic domain abolishes this kinase activity, indicating that Stk uses a phosphotransfer mechanism similar to the mechanism used by eukaryotic PKs . We provide evidence suggesting that stk is cotranscribed with cI from the phage promoter responsible for maintaining CI expression during lysogeny . The stk gene was identified in prophages obtained from independently isolated Stx-producing Escherichia coli clinical isolates, suggesting that selective pressure has maintained the stk gene in these pathogenic bacteria . Filamentous Bacteriophages of Vibrios Are Integrated into the dif-Like Site of the Host Chromosome. Tetsuya Iida, 2002.The dif site is located in the replication terminus region of bacterial chromosomes, having a function of resolving dimeric chromosomes formed during replication . We demonstrate that filamentous bacteriophages of vibrios, such as f237 (Vibrio parahaemolyticus) and CTX  (V . cholerae), are integrated into the dif-like site of host chromosome .
Amino Acid- and Purine Ribonucleoside-Induced Germination of Bacillus anthracis  Sterne Endospores: gerS Mediates Responses to Aromatic Ring Structures.John A. W. Ireland, 2002.Specific combinations of amino acids or purine ribonucleosides and amino acids are required for efficient germination of endospores of Bacillus anthracis Sterne, a plasmidless strain, at ligand concentrations in the low-micromolar range . The amino acid L-alanine was the only independent germinant in B . anthracis and then only at concentrations of >10 mM . Inosine and L-alanine both play major roles as cogerminants with several other amino acids acting as efficient cogerminants (His, Pro, Trp, and Tyr combining with L-alanine and Ala, Cys, His, Met, Phe, Pro, Ser, Trp, Tyr, and Val combining with inosine) . An ortholog to the B . subtilis tricistronic germination receptor operon gerA was located on the B . anthracis chromosome and named gerS . Disruption of gerS completely eliminated the ability of B . anthracis endospores to respond to amino-acid and inosine-dependent germination responses . The gerS mutation also produced a significant microlag in the aromatic-amino-acid-enhanced-alanine germination pathways . The gerS disruption appeared to specifically affect use of aromatic chemicals as cogerminants with alanine and inosine . We conclude that efficient germination of B . anthracis endospores requires multipartite signals and that gerS-encoded proteins act as an aromatic-responsive germination receptor .
IS1999 Increases Expression of the Extended-Spectrum ß-Lactamase VEB-1 in Pseudomonas aeruginosa. Daniel Aubert, 2003.The integron-borne blaVEB-1 gene encodes an extended-spectrum ß-lactamase . This gene was associated mostly with IS1999 and rarely with an additional IS2000 element in Pseudomonas aeruginosa isolates from Thailand, whereas IS1999 was only very rarely associated with blaVEB-1 in Enterobacteriaceae . Expression experiments and promoter study identified promoter sequences in IS1999 that increased the expression of VEB-1 in P . aeruginosa . Toxicity of Al to Desulfovibrio desulfuricans. J. E. Amonette, 2003.The toxicity of Al to Desulfovibrio desulfuricans G20 was assessed over a period of 8 weeks in a modified lactate C medium buffered at four initial pHs (5.0, 6.5, 7.2, and 8.3) and treated with five levels of added Al (0, 0.01, 0.1, 1.0, and 10 mM) . At pH 5, cell population densities decreased significantly and any effect of Al was negligible compared to that of the pH . At pHs 6.5 and 7.2, the cell population densities increased by 30-fold during the first few days and then remained stable for soluble-Al concentrations of <5 x 10-5 M . In treatments having total-Al concentrations of ≥1 mM, soluble-Al concentrations exceeded 5 x 10-5 M and limited cell population growth substantially and proportionally . At pH 8.3, soluble-Al concentrations were below the 5 x 10-5 M toxicity threshold and cell population density increases of 20- to 40-fold were observed . An apparent cell population response to added Al at pH 8.3 was attributed to the presence of large, spirilloidal bacteria (accounting for as much as 80% of the cells at the 10 mM added Al level) . Calculations of soluble-Al speciation for the pH 6.5 and 7.2 treatments that showed Al toxicity suggested the possible presence of the Al13O4(OH)24(H2O)127+ "tridecamer" cation and an inverse correlation of the tridecamer concentration and the cell population density . Analysis by 27Al nuclear magnetic resonance spectroscopy, however, yielded no evidence of this species in freshly prepared samples or those taken 800 days after inoculation . Exclusion of the tridecamer species from the aqueous speciation calculations at pHs 6.5 and 7.2 yielded inverse correlations of the neutral Al(OH)3 and anionic Al(OH)4- monomeric species with cell population density, suggesting that one or both of these ions bear primary responsibility for the toxicity observed .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
