|
|
|
|
|
|
Cardiolipin Domains in Bacillus subtilis Marburg Membranes. Fumitaka Kawai, 2004.Recently, use of the cardiolipin [CL]-specific fluorescent dye10-N-nonyl-acridine orange [NAO] revealed CL-rich domains inthe Escherichia coli membrane [E . Mileykovskaya and W . Dowhan,J . Bacteriol . 182: 1172-1175, 2000] . Staining of Bacillus subtiliscells with NAO showed that there were green fluorescence domainsin the septal regions and at the poles . These fluorescence domainswere scarcely detectable in exponentially growing cells of theclsA-disrupted mutant lacking detectable CL . In sporulatingcells with a wild-type lipid composition, fluorescence domainswere observed in the polar septa and on the engulfment and foresporemembranes . Both in the clsA-disrupted mutant and in a mutantwith disruptions in all three of the paralogous genes [clsA,ywjE, and ywiE] for CL synthase, these domains did not vanishbut appeared later, after sporulation initiation . A red shiftin the fluorescence due to stacking of two dye molecules andthe lipid composition suggested that a small amount of CL waspresent in sporulating cells of the mutants . Mass spectrometryanalyses revealed the presence of CL in these mutant cells.At a later stage during sporulation of the mutants the frequencyof heat-resistant cells that could form colonies after heattreatment was lower . The frequency of sporulation of these cellsat 24 h after sporulation initiation was 30 to 50% of the frequencyof the wild type . These results indicate that CL-rich domainsare present in the polar septal membrane and in the engulfmentand forespore membranes during the sporulation phase even ina B . subtilis mutant with disruptions in all three paralogousgenes, as well as in the membranes of the medial septa and atthe poles during the exponential growth phase of wild-type cells. The results further suggest that the CL-rich domains in the polar septal membrane and engulfment and forespore membranesare involved in sporulation. Loop Deletions Indicate Regions Important for FhuA Transport and Receptor Functions in Escherichia coli. Franziska Endriß, 2004.Precise deletions of cell surface-exposed loops of FhuA resulted in mutants of Escherichia coli with distinct phenotypes . Deletion of loop 3 or 11 inactivated ferrichrome transport activity . Deletion of loop 8 inactivated receptor activity for colicin M and the phages T1, T5, and  80 .
The loop 7 deletion mutant was colicin M resistant but fully phage
sensitive . The loop 4 deletion mutant was resistant to the
TonB-dependent phages T1 and
80
but fully sensitive to the TonB-independent phage T5 . The phenotypes
of the deletion mutants revealed important sites for the multiple
FhuA transport and receptor activities . The ligand binding sites are
nonidentical and are distributed among the entire exposed surface .
Presumably, FhuA evolved as a ferrichrome transporter and was
subsequently used as a receptor by the phages and colicin M, which
selected the same as well as distinct loops as receptor sites .
The Highly Conserved TldD and TldE Proteins of Escherichia coli Are Involved in Microcin B17 Processing and in CcdA Degradation. Noureddine Allali, 2002.Microcin B17 (MccB17) is a peptide antibiotic produced by Escherichia coli strains carrying the pMccB17 plasmid . MccB17 is synthesized as a precursor containing an amino-terminal leader peptide that is cleaved during maturation . Maturation requires the product of the chromosomal tldE (pmbA) gene . Mature microcin is exported across the cytoplasmic membrane by a dedicated ABC transporter . In sensitive cells, MccB17 targets the essential topoisomerase II DNA gyrase . Independently, tldE as well as tldD mutants were isolated as being resistant to CcdB, another natural poison of gyrase encoded by the ccd poison-antidote system of plasmid F . This led to the idea that TldD and TldE could regulate gyrase function . We present in vivo evidence supporting the hypothesis that TldD and TldE have proteolytic activity . We show that in bacterial mutants devoid of either TldD or TldE activity, the MccB17 precursor accumulates and is not exported . Similarly, in the ccd system, we found that TldD and TldE are involved in CcdA and CcdA41 antidote degradation rather than being involved in the CcdB resistance mechanism . Interestingly, sequence database comparisons revealed that these two proteins have homologues in eubacteria and archaebacteria, suggesting a broader physiological role . Conserved Filamentous Prophage in Escherichia coli O18:K1:H7 and Yersinia pestis Biovar orientalis. Mark D. Gonzalez, 2002.Microbial virulence is known to emerge by horizontal gene transfer mechanisms . Here we describe the discovery of a novel filamentous prophage, designated CUS-1, which is integrated into the chromosomal dif homologue of the high-virulence clone Escherichia coli O18:K1:H7 . An homologous chromosomal element (CUS-2) in Yersinia pestis biovar orientalis is integrated at the same relative location as CUS-1; both lysogenic E . coli and Y . pestis strains produce particles with properties expected of single-stranded DNA virions . CUS  is epidemiologically correlated with the emergence of K1 strains with increased virulence and with the Y . pestis biovar responsible for the current (third) plague pandemic .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
