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  • 1
    Electronic Resource
    Electronic Resource
    Divergent roles of RpoS in Escherichia coli under aerobic and anaerobic conditions (2005)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 244 (2005), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Escherichia coli exhibited different levels of rpoS expression and general stress resistance under aerobiosis and anaerobiosis. Expression measured using reporter gene fusions and protein levels was lower under anaerobic conditions. Consistent with earlier findings, rpoS mutants were selected in aerobic nutrient-limited cultures but rpoS mutants were not enriched under anaerobiosis. This result suggested that, despite its decreased level, RpoS had a function under anaerobic conditions not essential under aerobiosis. Competition experiments between rpoS+ and rpoS bacteria confirmed the advantage conferred by RpoS under anaerobiosis. In contrast, stress resistance assays suggested RpoS made a greater contribution to general stress resistance under aerobiosis than anaerobiosis. These results indicate a significant, but different role of RpoS in aerobic and anaerobic environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsle.2005.02.002
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  • 2
    Electronic Resource
    Electronic Resource
    Cysteine-22 and cysteine-38 are not essential for the functions of maltoporin (LamB protein) (1989)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 61 (1989), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Maltoporin in the outer membrane of Escherichia coli contains two cysteine residues, at positions 22 and 38 in the primary sequence. The role of these residues in determining structural stability, and their contributions to the maltoporin binding sites for maltodextrins and bacteriophage λ, was investigated. Site-directed mutagenesis was used to alter each of these residues to a serine. A double mutant lacking both cysteines was also isolated. None of the substitutions affected maltodextrin binding or the binding of phage λ, suggesting the variant proteins retain a native binding-site conformation. The mutants were assembled at wild-type levels into the outer membrane as maltoporin trimers but the temperature-stability of the trimer 〉 monomer dissociation was slightly reduced in the presence of the Cys 38 substitution. However, it is unlikely that the stability of trimers was due to disulfide linkages between subunits since the native trimers are stable under highly reducing conditions in the presence of SDS; more likely the Cys 〉 Ser substitutions slightly perturb intra- or inter-subunit hydrophobic interactions in regions predicted to span across the outer membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1989.tb03647.x
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  • 3
    Electronic Resource
    Electronic Resource
    Binding of Escherichia coli K-12 to cellulose (1984)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 25 (1984), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Escherichia coli K-12 populations containing up to 3 · 109 bacteria were reversibly retained by columns containing fibrous cellulose. Using chromatographic retention as an assay of attachment to cellulose, the factors affecting bacterial binding were investigated. Minimal binding was observed in the absence of ions or at high pH. Optimal binding was observed in the presence of low concentrations of divalent cations at any pH or at pH below 4 in the absence of divalent cations. Factors found not to significantly affect bacterial retention by cellulose included the culture conditions of the bacteria, the presence of surface appendages, the presence of various sugars during chromatography or variations in elution temperature between 0 and 70°C. These results suggest that mechanisms not dependent on appendages contribute to the adhesion of a bacterium to an inert surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1984.tb01366.x
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  • 4
    Electronic Resource
    Electronic Resource
    Epitope mapping by cysteine mutagenesis: Identification of residues involved in recognition by three monoclonal antibodies directed against LamB glycoporin in the outer membrane of Escherichia coli (1994)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 120 (1994), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Site-directed mutagenesis of the lamB gene was used to introduce individual cysteine substitutions at 20 sites in two regions (surface loops L7 and L8) of LamB protein significant in antibody recognition. Characterisation of cysteine mutants involved immunoblotting with three surface-specific monoclonal antibodies (mAb72, mAb302, mAb347) before and after incubation with thiol-specific reagents. In contrast to an earlier study that showed no amino acid changes affecting recognition by all three antibodies, changes at six amino acids were found to influence a common core epitope. These core sites included one residue (T336) in the predicted loop L7 containing amino acids 329–342 and four (Y379, N387, N389, K392, F398) in the large surface loop involving residues 370–412. Individual antibodies made additional but distinct contacts within the two studied regions, with mAb347 binding the most different and affected by seven substitutions in the 328–338 regions. The lamB mutants were also tested for phage λ receptor activity and starch binding before and after thiol modification and were useful in extending previous maps of these ligand binding sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1994.tb07056.x
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  • 5
    Electronic Resource
    Electronic Resource
    Maintaining a healthy SPANC balance through regulatory and mutational adaptation (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 57 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Stress protection is an important but costly contributor to bacterial survival. Two distinct forms of environmental protection share a common cost and a significant species-wide variability. Porin-mediated outer membrane permeability and the RpoS-controlled general stress response both involve a trade-off between self-preservation and nutritional competence, called the SPANC balance. Interestingly, different Escherichia coli strains exhibit distinct settings of the SPANC balance. It is tilted towards high stress resistance and a restricted diet in some isolates whereas others have broader nutritional capability and better nutrient affinity but lower levels of resistance. Growth- or stress-related selective pressures working in opposite directions (antagonistic pleiotropy) result in polymorphisms affecting porins and RpoS. Consequently, these important cellular components are present at distinct concentrations in different isolates. A generalized hypothesis to explain bacterial adaptation, based on the SPANC investigations, is offered. A holistic approach to bacterial adaptation, involving a gamut of regulation and mutation, is likely to be the norm in broadening the capabilities of a species. Indeed, there is unlikely to be a standard regulatory setting typical for all members of a species. Gene regulation provides a limited fine control for maintaining the right level of adaptation in a particular niche but mutational changes provide the coarse control for adaptation between the species-wide environments of free-living bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2005.04649.x
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  • 6
    Electronic Resource
    Electronic Resource
    OmpF changes and the complexity of Escherichia coli adaptation to prolonged lactose limitation (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 176 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The disaccharide lactose has no specific diffusion pathway across the outer membrane of Escherichia coli. At least three classes of spontaneous mutation affecting outer membrane permeability arose with each of three independent E. coli populations adapting to prolonged lactose limitation in chemostats. Both structural and regulatory mutations affecting OmpF porin predominated in isolates after 210–280 generations of culture. Six types of ompF mutation were found, including in-frame deletions and substitutions at Arg82 and Asp113, all affecting the channel constriction residues of OmpF. Isolates had increased susceptibility to antibiotics and were affected in the quantity of OmpF, LamB and OmpA proteins. A minimum of three or four mutations was evident in all isolates after 280 generations in a lactose-limited environment, in addition to lac mutations defined in previous studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb13689.x
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  • 7
    Electronic Resource
    Electronic Resource
    Differential expression of mal genes under cAMP and endogenous inducer control in nutrient-stressed Escherichia coli (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 16 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: LamB glycoporin has an important general role in carbohydrate uptake during growth at low extracellular sugar concentrations. lamB and mal regulon induction during glucose starvation and glucose-limited continuous culture was investigated using lacZ fusions. A low-level burst of lamB induction occurred upon entry into glucose starvation-induced stationary phase but returned to basal levels during continued nutrient deprivation. Glucose-limited continuous culture elicited much higher expression of transporter genes in the mal regulon, as well as [14C]-maltose-transport activity; malEFG and malKlamB operons in glucose-limited chemostats were expressed to close to half of the level of maltose-induced batch cultures. Limitation-induced expression was dependent on both Crp-cAMP and MalT activation but was independent of RpoS function. As expected for a gene with a Crp-controlled promoter, malT expression was maximal under conditions which elicited the highest cAMP levels, but lamB induction did not behave in a corresponding fashion. Rather, maximal lamB induction occurred at rapid but suboptimal growth rates with micromolar or submicromolar medium glucose. Maximal transport and lamB induction coincided with increased endogenous maltotriose (inducer) concentrations during growth on glucose. Hence regulation of glycoporin and the maltose-transport system is not a starvation- or stationary-phase response but facilitates the adaptation of Escherichia coli to low-nutrient environments through endoinduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.tb02397.x
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  • 8
    Electronic Resource
    Electronic Resource
    Role of outer membrane components in the nonspecific binding ofEscherichia coli to cellulose (1987)
    Springer
    Current microbiology 15 (1987), S. 347-353 
    Details
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The involvement of lipopolysaccharide and outer membrane proteins in the binding ofEscherichia coli to cellulose was investigated. Cellulose binding was assayed in defined strains with or without O-antigenic polysaccharide and in mutants with defects in lipopolysaccharide core synthesis. Binding was also tested in strains lacking major outer membrane proteins. Optimal cellulose binding was exhibited by rough strains and was reduced to various extents in the presence of different O-antigens. Core defects also reduced but did not abolish binding to cellulose. Reduced binding was also found in mutants lacking OmpC protein, but OmpC/OmpA double mutants orompB mutants lacking OmpC and OmpF were not affected. Mutants with reduced cellulose binding were also isolated directly through selection of nonbinding populations after chromatography on cellulose columns. Each of the independent isolates derived fromE. coli K12 with reduced cellulose binding had multiple mutations, with additional phenotypic changes such as phage resistance, increased sensitivity to bile salts, or altered patterns of outer membrane proteins. These results suggest that no single receptor that could be altered by mutation was responsible for the binding ofE. coli to cellulose. Rather, the nonspecific binding of cellulose was more likely to be due to interaction with, or the combined activity of, several integral outer membrane components that could be masked by O-antigen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01577593
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  • 9
    Electronic Resource
    Electronic Resource
    Selectivity in solute transport: Binding sites and channel structure in maltoporin and other bacterial sugar transport proteins (1989)
    New York, NY : Wiley-Blackwell
    BioEssays 10 (1989), S. 1-7 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A stereospecific binding site is not the only determinant governing the selectivity of transport proteins. An understanding of transport across cellular membranes requires a description of the different compartments within a transmembrane channel; evidence for the existence of these compartments comes from the selectivity properties of genetically modified maltoporin. Such compartments may also be of significance in determining the specificity of other transport proteins.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950100102
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  • 10
    Electronic Resource
    Electronic Resource
    The role of the Escherichia coli λ receptor in the transport of maltose and maltodextrins (1980)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 13 (1980), S. 101-116 
    Details
    ISSN: 0091-7419
    Keywords: λ receptor ; maltose-binding protein ; outer membrane permeability ; maltodextrin transport ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The λ receptor is a peptidoglycan-associated integral protein that spans the outer membrane. Beside its function in phage λ adsorption it participates in transport. The latter function can be summarized as follows: (1) Receptor allows the nonspecific permeation of small molecules other than maltose and maltodextrins (in close analogy to a molecular sieve). Here the only criterion for selectivity is size and it has the properties of an unspecific pore. In this respect, it is similar to the outer membrane proteins Ia, Ib, and Ic, the porins. (2) It is a binding protein for maltodextrins. Binding affinity is low but increases by a factor of 500 as the chain length of the maltodextrins increases. In contrast, the affinity of the periplasmic maltose-binding protein for maltose and maltodextrins is similarly high (in the μM range). (3) In the in vitro system of liposomes, the λ receptor facilitates specifically the diffusion of maltodextrins that exceed the size limit given by its porin function. This clearly demonstrates that the λ receptor alone is able to specifically overcome the permeability barrier of the outer membrane for maltodextrins. (4) From the genetic and kinetic analysis of maltose and maltodextrin transport, it can be concluded that the λ receptor interacts with the periplasmic maltose-binding protein. (5) Electron microscopic studies indicate a location for the maltose-binding protein in the outer cell envelope. This location is dependent on the presence of the λ receptor.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400130110
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