Ultrastructural studies on the inner and outer membranes of an unsaturated fatty acid auxotroph of Escherichia coli

Biochemical and morphological properties of membranes of unsaturated fatty acid auxotrophs of Salmonella typhimurium: effects of fluorinated myristic acids

In order to investigate the utility of the fluorine-19 nucleus as a spectroscopic probe, a fluorinated analog of myristic acid has been incorporated into the membrane lipids of an unsaturated fatty acid auxotroph of Salmonella typhimurium. It is capable of supporting limited growth at temperatures above 37 degrees C. Freeze-fracture electron microscopic examinations of the membrane ultrastructure show a temperature and fatty acid supplement-dependent segregation of intramembranous protein particles into distinct patches in the auxotrophic membrane leaving intramembranous protein-denuded areas. The occurrence of these patches seems to be related to the phase separation of membrane lipids. Corresponding changes in the transport and accumulation of methyl thio-beta-D-galactopyranoside and tetracycline are observed. However, transport of histidine does not appear to be dependent on the physical state of the membrane lipids. The auxotroph shows differences in growth and morphological characteristics from those of the wild type. Functions of both inner and outer membranes are shown to be affected as a response to the fatty acid chain composition of the lipids.

Modifications of the envelope of Chlamydia psittaci during its developmental cycle: freeze-fracture study of complementary replicas

Examination of complementary replicas obtained by freeze-fracture of Chlamydia psittaci revealed, at the level of the plasma membrane, a progressive differentiation of "crate-like formations," which likely correspond to transmembranal pores. Recognition of "early" and "late" stages observed in the intermediate bodies permitted detailed study of the developmental cycle of this chlamydia.

A confirmation of the phase behavior of Escherichia coli cytoplasmic membrane lipids by X-ray diffraction

The lipid fatty acid composition of the cytoplasmic membranes of Escherichia coli can be varied by growing an unsaturated fatty acid auxotroph in the presence of different fatty acid supplements. Electron spin resonance (ESR) studies of spin-label partitioning into the cytoplasmic membranes of different lipid fatty acid compositions as a function of temperature have been interpreted as indicating a broad order-to-disorder transition in the membrane lipids, the end points of the transition depending upon the fatty acid composition. We have utilized x-ray diffraction to confirm the ESR studies for three different fatty acid supplements (oleic, elaidic, and bromostearic). We found that the characteristic end-point temperatures detected by ESR were indeed the end-point temperatures of a broad order-to-disorder transition of the cytoplasmic membrane lipids. In addition, Patterson functions calculated from lamellar x-ray diffraction from partially oriented cytoplasmic membranes indicate a decrease in average membrane thickness upon fatty acid chain melting.

Effects of lipid phase transition of the freeze-cleaved envelope of Escherichia coli

We studied the fine structure of the envelope of Escherichia coli auxotroph K1060 after the cells were grown in the presence of one of the following fatty acids; oleic, palmitelaidic, or elidic acid. The cells were freeze-fractured after exposure to temperatures above and below the lipid phase transition range. As judged by freeze-etching methods, we observed that below the transition range the fracture plane of the inner membrane showed the typical aggregation of intramembranous particles (IMP) and concomitant development of areas devoid of IMP. In these areas we found a regular arrangement of equally spaced ridges, often intersected at 90 degrees by arrays of similar ridges. The ridges were composed of spherical particles measuring 4 to 5 nm in diameter. Formation and melting of these arrays took place within 15 to 30s after temperature shift-down or shift-up, respectively. Fixation in glutaraldehyde prevented these changes. The outer-membrane fracture plane revealed ordered areas to a lesser degree; these were discernible only by the regular arrangement of the IMP of the concave fracture plane. We interpret the data by suggesting that the pattern of ridges in E. coli K1060 is analogous to the band patterns described for artificial liposomes, and that the particles, possibly proteins, are lined up or extruded along the ridges during membrane lipid crystallization.

Functional organization of the outer membrane of escherichia coli: phage and colicin receptors as components of iron uptake systems

The functional interaction of outer membrane proteins of E. coli can be studied using phage and colicin receptors which are essential components of penetration systems. The uptake of ferric iron in the form of the ferrichrome complex requires the ton A and ton B functions in the outer membrane of E. coli. The ton A gene product is the receptor protein for phage T5 and is required together with the ton B function by the phages T1 and ø80 to infect cells and by colicin M and the antibiotic albomycin, a structural analogue of ferrichrome, to kill cells. The ton B function is necessary for the uptake of ferric iron complexed by citrate. Iron complexed by enterochelin is only transported in the presence of the ton B and feu functions. Cells which have lost the feu function are resistant to the colicins B, I or V while ton B mutants are resistant to all 3 colicins. The interaction of the ton A, ton B, and feu functions apparently permits quite different "substrates" to overcome the permeability barrier of the outer membrane. It was shown for ferrichrome dependent iron uptake that the complexing agent was not altered and could be used repeatedly. Only very low amounts of 3H-labeled ferrichrome were found in the cell. It is possible that the iron is mobilized in the membrane and that desferri-ferrichrome is released into the medium without having entered the cytoplasm. Growth on ferrichrome as the sole iron source was used to select revertants of T5 resistant ton A mutants. All revertants exhibited wild-type properties with the exception of partial revertants. In these 4 strains, as in the ton A mutants, the ton A protein was not detectable by SDS polyacrylamide gel electrophoreses of outer membranes. Albomycin resistant mutants were selected and shown to fall into 5 categories: 1) ton A; 2) ton B mutants; 3) mutants with no iron transport defects and normal ton A/ton B functions, which might be target site mutants; 4) mutants which were deficient in ferrichrome-mediated iron uptake but had normal ton A/ton B functions. We tentatively consider that the defect might be located in the active transport system of the cytoplasmic membrane; 5) a variety of mutants with the following general properties: most of them were resistant to colicin M, transported iron poorly, and, like ton B mutants, contained additional proteins in the outer membrane. The outer membrane protein patterns of wild-type and ton B mutant strains were compared by slab gel electrophoresis in an attempt to identify a ton B protein. It was observed that under most growth conditions, ton B mutants overproduced 3 proteins of molecular weights 74,000-83,000. In extracted, iron-deficient medium, both the wild-type and ton B mutant strains had similar large amounts of these proteins in their outer membranes. The appearance of these proteins was suppressed by excess iron in both wild-type and mutant. From this evidence it is apparent that the proteins appear as a response to low intracellular iron rather than being controlled by the ton B gene...