Molecular Microbiology
1365-2958
0950-382X
Anh Quốc
Cơ quản chủ quản: Wiley-Blackwell Publishing Ltd , WILEY
Lĩnh vực:
Molecular BiologyMicrobiology
Phân tích ảnh hưởng
Thông tin về tạp chí
Molecular Microbiology, the leading primary journal in the microbial sciences, publishes molecular studies of Bacteria, Archaea, eukaryotic microorganisms, and their viruses. Research papers should lead to a deeper understanding of the molecular principles underlying basic physiological processes or mechanisms. Appropriate topics include gene expression and regulation, pathogenicity and virulence, physiology and metabolism, synthesis of macromolecules (proteins, nucleic acids, lipids, polysaccharides, etc), cell biology and subcellular organization, membrane biogenesis and function, traffic and transport, cell-cell communication and signalling pathways, evolution and gene transfer. Articles focused on host responses (cellular or immunological) to pathogens or on microbial ecology should be directed to our sister journals Cellular Microbiology and Environmental Microbiology, respectively.
Các bài báo tiêu biểu
Screening for synthetic lethal mutants in <i>Escherichia coli</i> and identification of EnvC (YibP) as a periplasmic septal ring factor with murein hydrolase activity Summary Bacterial cytokinesis is driven by the septal ring apparatus, the assembly of which in Escherichia coli is directed to mid‐cell by the Min system. Despite suffering aberrant divisions at the poles, cells lacking the minCDE operon (Min– ) have an almost normal growth rate. We developed a generally applicable screening method for synthetic lethality in E. coli , and used it to select for transposon mutations (slm ) that are s ynthetically l ethal (or sick) in combination with Δm inCDEslm insertions mapped to envC (yibP ), proposed to encode a lysostaphin‐like, metallo‐endopeptidase that is exported to the periplasm by the general secretory (Sec) pathway. Min– EnvC– cells showed a severe division defect, supporting a role for EnvC in septal ring function. Accordingly, we show that an EnvC–green fluorescent protein fusion, when directed to the periplasm via the twin‐arginine export system, is both functional and part of the septal ring apparatus. Using an in‐gel assay, we also present evidence that EnvC possesses murein hydrolytic activity. Our results suggest that EnvC plays a direct role in septal murein cleavage to allow outer membrane constriction and daughter cell separation. By uncovering genetic interactions, the synthetic lethal screen described here provides an attractive new tool for studying gene function in E. coli .
Tập 52 Số 5 - Trang 1255-1269 - 2004
Rv3133c/<i>dosR</i> is a transcription factor that mediates the hypoxic response of <i>Mycobacterium tuberculosis</i> Summary Unlike many pathogens that are overtly harmful to their hosts, Mycobacterium tuberculosis can persist for years within humans in a clinically latent state. Latency is often linked to hypoxic conditions within the host. Among M. tuberculosis genes induced by hypoxia is a putative transcription factor, Rv3133c/DosR. We performed targeted disruption of this locus followed by transcriptome analysis of wild‐type and mutant bacilli. Nearly all the genes powerfully regulated by hypoxia require Rv3133c/DosR for their induction. Computer analysis identified a consensus motif, a variant of which is located upstream of nearly all M. tuberculosis genes rapidly induced by hypoxia. Further, Rv3133c/DosR binds to the two copies of this motif upstream of the hypoxic response gene alpha‐crystallin. Mutations within the binding sites abolish both Rv3133c/DosR binding as well as hypoxic induction of a downstream reporter gene. Also, mutation experiments with Rv3133c/DosR confirmed sequence‐based predictions that the C‐terminus is responsible for DNA binding and that the aspartate at position 54 is essential for function. Together, these results demonstrate that Rv3133c/DosR is a transcription factor of the two‐component response regulator class, and that it is the primary mediator of a hypoxic signal within M. tuberculosis .
Tập 48 Số 3 - Trang 833-843 - 2003
The interaction of naturally elaborated blebs from serum‐susceptible and serum‐resistant strains of <i>Neisseria gonorrhoeae</i> with normal human serum Summary We studied the interaction of normal human serum immunoglobulins with outer‐membrane bleb antigens of Neisseria gonorrhoeae. Gonococcal 68000 Dalton and Lip (H.8 antigen) outer‐membrane proteins were recognized by normal human serum immunoglobulins in blebs from serum‐resistant strains, but not in blebs from serum‐susceptible strains. The addition of blebs from a serum‐resistant strain to bactericidal assays resulted in significantly greater inhibition of serum killing than the addition of blebs from a serum‐susceptible strain. Our results indicate that blebs from two serum‐resistant gonococcal strains have an enhanced ability to bind and remove cell‐targeted bactericidal factors, and that outer‐membrane bleb‐bing may contribute to serum resistance.
Tập 6 Số 6 - Trang 729-734 - 1992
The transfer region of IncI1 plasmid R64: similarities between R64 <i>tra</i> and <i>Legionella icm/dot</i> genes The entire nucleotide sequence of the transfer region of IncI1 plasmid R64 was determined together with previously reported sequences. Twenty‐two transfer genes, traE–Y and nuc , were newly identified in the present study. The protein products of 17 genes were detected by maxicell experiments or by the T7 RNA polymerase expression system. Mutagenesis experiments indicated that 16 genes were indispensable for R64 transfer both in liquid and on surfaces. In summary, the R64 transfer region located within an ≈ 54 kb DNA segment was shown to encode the most complex transfer system so far studied. It contains at least 49 genes and may produce 58 different proteins as a result of shufflon DNA rearrangement and overlapping genes. Among the 49 genes, 23 tra, trb and nik genes have been shown to be indispensable for R64 conjugal transfer in liquid and on surfaces. Twelve additional pil genes are required only for liquid matings. The amino acid sequences of 10 R64 tra /trb products share similarity with those of the icm /dot products of Legionella pneumophila that are responsible for its virulence, suggesting that the R64 transfer and L. pneumophila icm/dot systems have evolved from a common ancestral genetic system.
Tập 35 Số 6 - Trang 1348-1359 - 2000
A transcription terminator signal necessary for plasmid Collb‐P9 replication Replication of the Inclα plasmid CoIIb‐P9 requires the repZ gene, which encodes an essential, unstable initiator protein termed RepZ. Although many functional features of the CoIIb‐P9 replicon resemble those of structurally unrelated IncFII plasmids R1 and NR1, the role of transcription of repZ towards the replication origin is poorly understood. Using a series of deletion and substitution mutants of the CoIIb‐P9 replicon, we found that RepZ prefers to act in cis and that a spacer sequence between repZ and the origin is required for replication. This spacer element, referred to as CIS , retained strong transcription terminator activity. Efficient transcription terminators, whether Rho‐dependent or ‐independent, were capable of replacing CIS function for in vivo replication; CoIIb‐P9 replicated better as transcription terminated more efficiently within CIS . When the CIS element was substituted for by a strong Rho‐dependent terminator, such as λ tR1 or E. coli trp tt' , in vivo replication of these recombinant replicons became dependent on the Rho factor, in contrast to the authentic CoIIb‐P9 replicon.
Tập 17 Số 2 - Trang 291-301 - 1995
Characterization of the micro‐environment of <i>Salmonella typhimurium</i>–containing vacuoles within MDCK epithelial cells Summary Salmonella typhimurium has the capacity to enter into and multiply within epithelial cells. During the entire intracellular stage, bacteria are enclosed within a vacuole. To characterize the micro–environment of the bacteria–containing vacuoles, we have used a new method to measure the expression levels of several S. typhimurium genes in intracellular bacteria within Madin–Darby canine kidney (MDCK) epithelial cells. Our study was based on the determination of ß–galactosidase activity derived from lacZ transcriptional fusions using the highly sensitive substrate fluorescein–di–ß–D–galactoside (FDG). Expression of the iroA and mgtB genes (induced by Fe2+ and Mg2+ limitation respectively), and cadA (induced by pH 6.0 in the presence of lysine, with enhanced expression under anaerobiosis) were characterized at different post–infection times. High intracellular expression levels were detected for the iroA and mgtB genes, suggesting that the concentrations of free Fe2+ and Mg2+ in the vacuole may be low. cadA actitvity was detected only at early post–infection times (4 h), suggesting that the vacuole may have a mild–acidic pH, and oxygen and lysine present at this time. Globally, the results reported indicate that the use of a highly sensitive ß–galactosidase substrate can provide information about the micro–enviroment within which an intracellular pathogen, such as S. typhimurium , resides.
Tập 6 Số 22 - Trang 3289-3297 - 1992
Molecular genetic analysis of the <i>moa</i> operon of <i>Escherichia coli</i> K‐12 required for molybdenum cofactor biosynthesis Summary A 3.2 kb chromosomal DNA fragment which complements the defects in a series of twelve moa ::Mucts insertion mutants has been sequenced. Five open reading frames (ORFs) were identified and these are arranged in a manner consistent with their forming an operon. The encoded proteins (MoaA‐MoaE) have predicted molecular weights of 37346, 18665, 17234, 8843 and 16981 respectively. Examination of subclones of the whole locus in an expression system demonstrated the predicted products. N ‐terminal amino acid sequences for the moa A, B, C and E products confirmed the translational starts. Genetic analysis distinguished four classes of moa mutants corresponding to genes moaA, C, D and E. Potential promoter sequences upstream of moaA and a possible transcription termination signal have been identified. Genetic analysis of the chlA1 and chlM mutants, which have been biochemically characterized as defective in molybdopterin biosynthesis, indicates that these carry lesions in moaA and moaD respectively. The moa locus is orientated clockwise at 17.7 minutes in the chromosome.
Tập 8 Số 6 - Trang 1071-1081 - 1993
The receptor for <i>Bacillus thuringiensis</i> CrylA(c) delta‐endotoxin in the brush border membrane of the lepidopteran <i>Manduca sexta</i> is aminopeptidase N Summary A 120 kDa glycoprotein in the larval midgut membrane of the Iepidopteran Manduca sexta , previously identified as a putative receptor for Bacillus thuringiensis CrylA(c) δ‐endotoxin, has been purified by a combination of protoxin affinity Chromatography and anion exchange chromatography. In immunoblotting experiments, the purified glycoprotein has the characteristics predicted of the receptor: it binds CrylA(c) toxin In the presence of GlcNAc but not GalNAc; it binds the lectin SBA; but it does not bind CrylB toxin. N‐terminal and internal amino acid sequences obtained from the protein show a high degree of similarity with the enzyme aminopeptidase N (EC 3.4.11.2). When assayed for aminopeptidase activity, purified receptor preparations were enriched 5.3‐fold compared to M. sexta brush border membrane vesicles. We propose that the receptor for CrylA(c) toxin in the brush border membrane of the lepidopteran M. sexta is the metalloprotease aminopeptidase N.
Tập 11 Số 3 - Trang 429-436 - 1994
Rv1818c‐encoded PE_PGRS protein of <i>Mycobacterium tuberculosis</i> is surface exposed and influences bacterial cell structure Summary Identification of the novel PE multigene family was an unexpected finding of the genomic sequencing of Mycobacterium tuberculosis . Presently, the biological role of the PE and PE_PGRS proteins encoded by this unique family of mycobacterial genes remains unknown. In this report, a representative PE_PGRS gene (Rv1818c/PE_PGRS33 ) was selected to investigate the role of these proteins. Cell fractionation studies and fluorescence analysis of recombinant strains of Mycobacterium smegmatis and M. tuberculosis expressing green fluorescent protein (GFP)‐tagged proteins indicated that the Rv1818c gene product localized in the mycobacterial cell wall, mostly at the bacterial cell poles, where it is exposed to the extracellular milieu. Further analysis of this PE_PGRS protein showed that the PE domain is necessary for subcellular localization. In addition, the PGRS domain, but not PE, affects bacterial shape and colony morphology when Rv1818c is overexpressed in M. smegmatis and M. tuberculosis . Taken together, the results indicate that PE_PGRS and PE proteins can be associated with the mycobacterial cell wall and influence cellular structure as well as the formation of mycobacterial colonies. Regulated expression of PE genes could have implications for the survival and pathogenesis of mycobacteria within the human host and in other environmental niches.
Tập 52 Số 3 - Trang 725-733 - 2004
<i>Helicobacter pylori cad</i>A encodes an essential Cd(II)–Zn(II)–Co(II) resistance factor influencing urease activity Inactivation of Helicobacter pylori cad A, encoding a putative transition metal ATPase, was only possible in one of four natural competent H. pylori strains, designated 69A. All tested cad A mutants showed increased growth sensitivity to Cd(II) and Zn(II). In addition, some of them showed both reduced 63 Ni accumulation during growth and no or impaired urease activity, which was not due to lack of urease enzyme subunits. Gene complementation experiments with plasmid (pY178)‐derived H. pylori cad A failed to correct the deficiencies, whereas resistance to Cd(II) and Zn(II) was restored. Moreover, pY178 conferred increased Co(II) resistance to both the cad A mutants and the wild‐type strain 69A. Heterologous expression of H. pylori cad A in an Escherichia coli znt A mutant resulted in an elevated resistance to Cd(II) and Zn(II). Expression of cad A in E. coli SE5000 harbouring H. pylori nixA , which encodes a divalent cation importer along with the H. pylori urease gene cluster, led to about a threefold increase in urease activity compared with E. coli control cells lacking the H. pylori cad A gene. These results suggest that H. pylori Cad A is an essential resistance pump with ion specificity towards Cd(II), Zn(II) and Co(II). They also point to a possible role of H. pylori CadA in high‐level activity of H. pylori urease, an enzyme sensitive to a variety of metal ions.
Tập 33 Số 3 - Trang 524-536 - 1999