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L Leive

Publications and source records attributed to L Leive.

At least 37 records · Page 2Linked to original sources
PubMed1982

A surface polysaccharide of Escherichia coli O111 contains O-antigen and inhibits agglutination of cells by O-antiserum.

The repeating pentasaccharide of O-antigen from Escherichia coli O111 contains galactose, glucose, N-acetylglucosamine, and colitose, the latter representing the major antigenic determinant. Phenol extraction of this strain was previously shown to release two fractions (I and II) containing O-antigen carbohydrate, and both fractions were believed to be lipopolysaccharide. We have now characterized fractions I and II and conclude that only fraction II represents lipopolysaccharide. Fraction II contains phosphate, 2-keto-3-deoxyoctonate, beta-hydroxymyristic acid, and potent endotoxin activity, whereas fraction I was deficient in all of these properties of the lipid A and core oligosaccharide regions of lipopolysaccharide. Fractions I and II each represented 50% of the total cellular O-antigen, and both were present on the cell surface. Both fractions were metabolically stable, and no precursor-product relationship existed between them. Fraction II had a number-average molecular weight of 15,800, corresponding to an average of 12 O-antigen repeats per molecule. In contrast, fraction I had a number-average molecular weight of 354,000, corresponding to an average of 404 O-antigen repeats per molecule. Before heat treatment, cells of E. coli O111 are poorly agglutinated by O-serum; although this indicates the presence of a capsule, the corresponding K-antigen was never detected. We conclude that fraction I, when present on the cell surface, inhibits agglutination of unheated cultures of E. coli O111 by O-serum because: (i) a variant strain which lacks fraction I was agglutinated by O-serum without prior heating; (ii) erythrocytes coated with purified fraction I behaved like bacteria containing fraction I in showing inhibition of O-serum agglutination; and (iii) heat treatment released fraction I and rendered bacterial cells agglutinable in O-serum.

Agglutination↗
PubMed1982

Phagocytosis of bacteria by macrophages: changing the carbohydrate of lipopolysaccharide alters interaction with complement and macrophages.

Salmonella transductants and recombinants differing the O-antigenic side chain of their lipopolysaccharide are taken up at different rates by the murine macrophage-like cell line J774. Bacteria containing abequose, mannose, rhamnose, and galactose in O-antigenic side chain were taken up at the slowest rate; the one containing tyvelose instead of abequose was taken up at an intermediate rate; and the one containing mannose, N-acetylglucosamine, and glucose, instead of the above sequence, was taken up at the highest rate. These rates correlate well with the known virulence of these strains; the most virulent is the one taken up slowest, the one taken up at an intermediate rate is less virulent, and the one taken up fastest is the least virulent. The differences in ingestion rates reflect differences in affinity of the bacteria for the macrophages and not in the rate of ingestion once interaction has occurred, suggesting a receptor-mediated process. The majority of uptake is probably dependent on complement, as shown by the requirement for a serum component(s) destroyed by heating at 56 degrees C or by incubation with zymosan. Specific antibody is not required. We therefore postulate that relative virulence in vivo may reflect the relative ability of the polysaccharide of bacterial lipopolysaccharide to activate complement, thus determining the susceptibility of the bacteria to ingestion via the complement receptor of phagocytic cells.

Animals↗
PubMed1979

Two mutations which affect the barrier function of the Escherichia coli K-12 outer membrane.

Two genetically distinct classes of novobiocin-supersensitive mutants were isolated from Escherichia coli K-12. One class, given the phenotypic name NbsA, lies at 10 min on the E. coli chromosome. The order of the genes in this region, based on transductional analyses, is proC NbsA plsA purE. The second, NbsB, lies at 80 min. The order of the genes in this region, based on transduction analyses, is xyl cysE NbsB pyrE. Both classes of mutants show increased sensitivity to hydrophobic drugs but are different: NbsA cells tend to be more sensitive to cationic agents, whereas NbsB cells show the opposite tendency. The sole detectable biochemical alteration in NbsA strain is greater than 90% reduction in the phosphate content of the lipid A region of the lipopolysaccharide. The NbsB mutation results in lipopolysaccharide that contains primarily the stereoisomer D-glycero-D-mannoheptose, rather than L-glycero-D-mannoheptose, and which contains very little of the distal sugars. Since NbsA strains have apparently normal outer membrane proteins and total cellular phospholipids, changes solely in lipopolysaccharide can increase permeability to certain hydrophobic antibiotics. Complementation studies indicate that the NbsA marker is probably allelic with acrA. In addition, the NbsB marker is genetically and phenotypically similar to the rfaD locus of Salmonella typhimurium. For this reason, the phenotypic designations NbsA and NbsB have been changed to the genotypic designations acrA and rfaD, respectively.

Cell Membrane↗
PubMed1977

Effect of variations in lipopolysaccharide on the fluidity of the outer membrane of Escherichia coli.

The lipid hydrocarbon chains in the outer membrane of gram-negative bacteria appear from previous experiments to be less mobile than in the cytoplasmic membrane. To determine whether lipopolysaccharide, a unique outer membrane component, is a cause of this restricted mobility, outer membranes differing in the amount of lipopolysaccharide, and the length of the polysaccharide side chain, were prepared from Escherichia coli J5. Cytoplasmic membranes were prepared for comparison. The probes, 5- and 12-doxylstearate, were introduced into these membranes, electron spin resonance spectra were analyzed, and the order parameter (S) and empirical motion parameter (tau0) were calculated. Outer membrane preparations containing long chain lipopolysaccharide were much less fluid by these criteria than were preparations containing short chain lipopolysaccharide. Removing about 40% of the lipopolysaccharide from the former preparations greatly increased their fluidity. The lipid in the cytoplasmic membrane preparations was more fluid than in the outer membrane and cytoplasmic membranes were similar to each other regardless of the composition of the outer membrane. These results indicate that lipopolysaccharide, and especially the polysaccharide portion, directly or indirectly causes the restricted mobility of the lipid hydrocarbon chains observed in the outer membrane.

Cell Membrane↗
PubMed1977

Domains involving nonrandom distribution of lipopolysaccharide in the outer membrane of Escherichia coli.

The present data demonstrate that the outer membrane of Escherichia coli contains domains of lipopolysaccharide that do not intermix freely with each other. A strain of E. coli lacking galactose epimerase was grown with galactose, for varying periods of time, which permits formation of a long polysaccharide, and without galactose, which results in a short polysaccharide. Such cultures yielded outer membrane fragments that were heterogeneous in lipopolysaccharide composition, some containing more long- than short-chain lipopolysaccharide, and vice versa. The kinetics of formation of these fragments suggest that lipopolysaccharide initially enters the membrane at points from which it can diffuse but ultimately is organized into domains that do not mix with each other, at least when lipopolysaccharides or different composition are present in the same organism.

Cell Membrane↗
PubMed1977

Genetic analysis of Escherichia coli O111:B4, a strain of medical and biochemical interest.

Procedures have been worked out which allow, for the first time, the genetic analysis of Escherichia coli O111:K58:H2 (O111:B4). The approximate map position of mutant loci was determined by mating with 15 Hfr strains of E. coli K-12. In addition, P1 transduction procedures were used for establishing relative gene order and linkage for any region of the E. coli O111:B4 chromosome. To obtain these, it was necessary to select for a rare P1 lysogen since E. coli O111:B4 is resistant to phage P1. Finally, genetic homology between E. coli strains K-12 and O111:B4 is suggested since they can form stable haploid hybrids, and several loci have similar map positions in the two strains.

Chromosome Mapping↗
PubMed1977

Effect of ethylenediaminetetraacetate upon the surface of Escherichia coli.

The effect of ethylenediaminetetraacetate (EDTA) on the envelope of two strains of Escherichia coli (B and Cla) was studied with freeze-fracturing methods. Untreated cells showed the outer membrane's outer surface with a fine texture of randomly spaced depressions of about 4.5-nm diameter; small areas with symmetrical arrangements of structural surface elements were also observed. The outer membrane's fracture plane revealed a random distribution of particles on its "concave" plane, only occasionally interrupted by particle-free areas. The "convex" aspect of the outer membrane's fracture plane showed only a few scattered particles. The cleavage plane of the inner membrane was often interrupted by many localized elevated plateaus, at which the cleaving process had, for short distances, switched to the outer membrane. The effects of EDTA treatment were mainly seen in the structure of the freeze-etched outer membrane: (i) the pits as well as the symmetrical surface elements of the outer membrane's outer surface had disappeared; (ii) a number of plateaus (about 20 to 50/cell) were seen at which a cleavage plane within the inner membrane had switched to the hydrophobic portion of the outer membrane (outer membrane's fracture plane). These plateaus were also visible in untreated cells; however, EDTA treatment apparently caused an increased exposure of plateaus. Surface areas, exposed by freeze-etching, revealed the underlying plateaus as elevations in the surface contour of the cell, suggesting a slower etching rate in the zones of the plateaus relative to the rest of the outer membrane. Well-defined, particle-free patches in the outer membrane's fracture plane, concave, were more frequent and larger in size after EDTA treatment than in the controls. In the presence of glycerol, the cells often cleaved in the outer membrane's fracture plane, but isolated plateaus were rarely observed. After metabolic poisoning of cells for 15 to 25 min at 37 degrees C, the plateaus had widened. These data suggest that the material of the plateaus has a slow rate of lateral diffusion. Placement of EDTA-treated cells in fresh medium at 37 degrees C caused, after 3 to 5 min, the reoccurrence of the pitted surface structure. We propose that the plateaus represent localized zones, at which newly synthesized lipopolysaccharide has been inserted.

Cell Membrane↗
PubMed1976

Mode of insertion of lipopolysaccharide into the outer membrane of escherichia coli.

A mutant of Escherichia coli that lacks uridine 5'-diphosphate galactose-4-epimerase makes lipopolysaccharide with less carbohydrate than the parent, unless galactose is present during growth. Carbohydrate is dense, and the outer membrane, which contains lipopolysaccharide, was found to be denser when isolated from cells grown with galactose then when galactose was omitted. Cells given galactose after growth in its absence rapidly formed dense regions within the outer membrane that disappeared when galactose was removed. These results indicate that lipopolysaccharide enters the outer membrane nonrandomly at a minimum of 10 to 22 discrete "insertion points." Isopycnic centrifugation provides a method for isolating these regions.

Carbohydrate Epimerases↗
PubMed1975

Fractions of lipopolysaccharide from Escherichia coli O111:B4 prepared by two extraction procedures.

Lipopolysaccharides have been extracted from Escherichia coli O111:B4 by phenol extraction and by a new method employing aqueous butanol. Both methods yield very similar lipopolysaccharide preparations. Gel filtration chromatography of either preparation yields two physically and chemically distinct lipopolysaccharide fractions. One fraction contains lipopolysaccharide molecules with long antigenic side chains. It acts like a highly asymmetric unit with an apparent weight of 1.5 times 10-6 and is not dissociated by detergents or deacylation. The second fraction has a short antigenic side chain and can be dissociated by sodium dodecyl sulfate and Triton X-100 into units of approximately 90,000. Some properties of the lipopolysaccharide fractions vary with the method of extraction.

Butanols↗
PubMed1974

Status of women microbiologists.

The general picture that emerges from this study is that the woman microbiologist, upon entering the professional job market, faces (i) slower advancement; (ii) restricted extramural recognition; and (iii) fewer positions of a supervisory or administrative nature, when compared to men. Most striking is the salary differential, which increases with increasing educational level, with increasing rank, and with increasing seniority. From the beginning of her professional training, the woman microbiologist feels handicapped by lack of encouragement and proper role models. She generally receives little advice regarding her professional future and rarely feels pushed to take the most challenging position. Should she be married, she feels that her mobility is severely restricted. Even though the subjective nature of these feelings may be interpreted as projections of failure, subtle inducements for women to stay at lower levels may well exist, in addition to more objective measurements, such as lower salary levels and slower professional advancement. Despite these handicaps, professional women continue to work. As a group, they work for the same reasons that men do, they work as long and as hard as men do, and they remain at their positions as long as men do. Women and men rate themselves equally as to job performance, degree of independence, and publication rate. On the basis of this study, it should not be surprising that women professionals are less visible than men and that only a small proportion of women become what is considered successful by the usual external criteria. If women were to receive continued encouragement, scientific contact, and professional recognition at each stage of their professional lives, they would undoubtedly become more visible. The lack of encouragement and selfconfidence leading to isolation, which then leads to lack of recognition, is a vicious circle that must be broken for the woman professional. This can be done most easily for the beginning student. For older women, there must be increased placement in positions of responsibility and visibility. Protective practices that discourage women from entering arenas of competition can only be viewed as discrimination on the basis of sex, since women professionals are rarely given the choice between being protected and being independent. Unexpectedly, this study illustrates the lower status of another group of individuals who are considered deviants from the expected roles of the established society-single men with doctorates, who were found in the positions predominately filled by women. In conclusion, this study of a select group of scientists probably has general applicability to all women professionals in their roles vis-à-vis men. Examination and documentation of discriminatory practices based on sex points to the areas in which women must direct their demands for equality.

Economics↗