Correlation between metabolism of phosphatidylglycerol and membrane synthesis in Escherichia coli

Influence of cluster formation of acidic phospholipids on decrease in the affinity for ATP of DnaA protein

DnaA protein is the initiator of chromosomal DNA replication in Escherichia coli. We examined the influence of artificial mixed membrane composed of synthetic acidic (phosphate) lipid and basic (ammonium) lipid on the affinity of DnaA protein for ATP. Two sets of acidic and basic lipids with distinguishable numbers of hydrophobic alkyl chains were devised. Synthetic membranes made of the sole acidic lipid but not the basic bilayers inhibited the ATP binding to DnaA protein and stimulated the release of ATP from the ATP-DnaA complex. The basic bilayer-forming compounds served as the matrix for the guest acidic lipids. Acidic lipids dispersed in the basic matrix membrane had little effect on ATP binding and on ATP release. Conversely, acidic lipids forming cluster structures in the mixed artificial membranes inhibited the ATP binding and stimulated the release of ATP. These observations suggest that in mixed lipid bilayers, a cluster structure of acidic lipids seems to be an important parameter to decrease the affinity of DnaA protein for ATP.

Interactions between DNA replication-related proteins and phospholipid vesicles in vitro

DNA and phospholipids share a common motif recognizable by proteins. It has been my hypothesis that there are DNA binding proteins which interact with phospholipid membranes and that their activities in DNA replication, transcription, and recombination, are likely to be regulated by phospholipids. I describe here examples of replication-related proteins, the activities of which are modified by acidic phospholipids in vitro.

Metabolic regulations and biological functions of phospholipids in Escherichia coli

Extensive genetic and biochemical studies in the last two decades have elucidated almost completely the framework of synthesis and turnover of quantitatively major phospholipids in E. coli. The knowledge thus accumulated has allowed to formulate a novel working model that assumes sophisticated regulatory mechanisms in E. coli to achieve the optimal phospholipid composition and content in the membranes. E. coli also appears to possess the ability to adapt phospholipid synthesis to various cellular conditions. Understanding of the functional aspects of E. coli phospholipids is now advancing significantly and it will soon be able to explain many of the hitherto unclear cell's activities on the molecular basis. Phosphatidylglycerol is believed to play the central role both in metabolism and functions of phospholipids in E. coli. The results obtained with E. coli should undoubtedly be helpful in the study of more complicated phospholipid metabolism and functions in higher organisms.

Synthesis of the cell surface during the division cycle of rod-shaped, gram-negative bacteria

When the growth of the gram-negative bacterial cell wall is considered in relation to the synthesis of the other components of the cell, a new understanding of the pattern of wall synthesis emerges. Rather than a switch in synthesis between the side wall and pole, there is a partitioning of synthesis such that the volume of the cell increases exponentially and thus perfectly encloses the exponentially increasing cytoplasm. This allows the density of the cell to remain constant during the division cycle. This model is explored at both the cellular and molecular levels to give a unified description of wall synthesis which has the following components: (i) there is no demonstrable turnover of peptidoglycan during cell growth, (ii) the side wall grows by diffuse intercalation, (iii) pole synthesis starts by some mechanism and is preferentially synthesized compared with side wall, and (iv) the combined side wall and pole syntheses enclose the newly synthesized cytoplasm at a constant cell density. The central role of the surface stress model in wall growth is distinguished from, and preferred to, models that propose cell-cycle-specific signals as triggers of changes in the rate of wall synthesis. The actual rate of wall synthesis during the division cycle is neither exponential nor linear, but is close to exponential when compared with protein synthesis during the division cycle.

A minor arginine tRNA mutant limits translation preferentially of a protein dependent on the cognate codon

The Escherichia coli argU gene encodes a rare arginine tRNA (anticodon UCU) that translates the similarly rare AGA codon. The argU10(Ts) mutation is a transition that changes the first nucleotide of the mature tRNA from G to A, presumably destabilizing the acceptor stem. This mutation, when present in haploid condition in the chromosome, reduces the growth rate at 30 degrees C and results in cessation of growth after 60 to 90 min at 43 degrees C. The mutation also preferentially limits (compared with total protein synthesis) translation of an induced gene that depends on five AGA codons, i.e., the lambda cI repressor gene. Translation of another inducible protein, beta-galactosidase, which does not involve AGA codons, was inhibited to a much lesser extent. The chromosomal argU(Ts) mutation also confers the Pin phenotype, that is, loss of ability of the host, as a P2 lysogen, to inhibit growth of bacteriophage lambda, probably the result of reduced translation of the P2 old gene, which contains five AGA codons (E. Haggård-Ljungquist, V. Barreiro, R. Calendar, D. M. Kurnit, and H. Cheng, Gene 85:25-33, 1989).

The Escherichia coli dnaJ mutation affects biosynthesis of specific proteins, including those of the lac operon

Temperature-sensitive dnaJ mutants of Escherichia coli showed a thermosensitive defect in the synthesis of beta-galactosidase. Synthesis of the lac mRNA was greatly reduced at the restrictive temperature. The mutants were also conditionally defective in the synthesis of a subset of membrane proteins such as succinate dehydrogenase, whereas the synthesis of anthranilate synthetase, encoded by trpED, as well as that of most cellular proteins, was unaffected at the restrictive temperature. The defect was specific for the dnaJ mutants among several dna mutants which are known to be involved in the initiation of DNA synthesis: dnaK, dnaA, and dnaB mutants synthesized each of these proteins normally even at the restrictive temperature. At the restrictive temperature, growth of the dnaJ mutants was arrested at a specific stage of the cell cycle.

Early increases in the frequency of DNA initiations and of phospholipid synthesis discontinuities after nutritional shift-up in Escherichia coli

Cultures of Escherichia coli (strains ML30 and K12 AB1157), synchronized by repeated phosphate starvation, were submitted to nutritional shifts-up at various cell ages. The progression of the replication forks was assessed by DNA-DNA hybridization of pulse-labelled chromosomal DNA with plasmid DNA probes containing specific chromosomal sequences. The rate of phospholipid synthesis and its cyclic discontinuities were measured by continuous and pulse labelling with palmitate. The DNA-DNA hybridization experiments showed that a shift-up induces a burst of initiation from the oriC region. These hybridization results, taken together with older data from the literature, suggest that most DNA initiations belonging to this burst are not followed by complete replication. Following a shift-up, the rate of phospholipid synthesis is maintained for 13-20 min, depending on cell age at shift-up, then doubles. The new steady-state rate of phospholipid synthesis is reached through a series of three doublings, while the cell mass doubles approximately twice. This discrepancy brings the rate of phospholipid synthesis per mass unit to its steady-state postshift value.

Lipid biosynthesis in synchronized cultures of the photosynthetic bacterium Rhodopseudomonas sphaeroides

Lipid biosynthesis has been studied in photosynthetic cultures of Rhodopseudomonas sphaeroides that had been synchronized by stationary-phase cycling or by a centrifugation selection procedure. Synchrony index values in the range 0.70-0.80 were obtained for the first cell cycle with both synchronization methods. The major membrane lipids phosphatidylethanolamine and phosphatidylglycerol were accumulated discontinuously during the cell cycle, their mass doubling immediately before cell division. This accumulation of lipid corresponded to peaks in incorporation of radioactivity from either [1-14C]acetate or [2-3H]glycerol into individual acyl lipids as measured in individual portions of bacteria. For phosphatidylglycerol an additional peak of incorporation of radioactivity from [2-3H]glycerol was found midway through the cell cycle. In spite of their rather similar endogenous fatty acid compositions, the individual phosphoacylglycerols showed distinctive patterns of incorporation of radioactivity from [1-14C]acetate into their acyl moieties. The discontinuous synthesis of acyl lipids observed in cultures of Rhodopseudomonas sphaeroides synchronized by either stationary-phase cycling or centrifugation selection procedures contrasted with the accumulation of chlorophyll-protein complexes whose amounts were found to increase throughout the cell cycle. The implications of these findings for the control of lipid synthesis in bacterial photosynthetic membranes are discussed.

Changes in the composition of membrane phospholipids during the cell cycle of Escherichia coli

Phospholipid concentrations have been estimated throughout the successive cell cycle in synchronously growing culture of E. coli B/r. Total phospholipid phosphorus was shown to be doubled in the period of time between two cell divisions, whereas during the division itself it did not change. Phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) exhibit a stepwise increase during the cell cycle. It should be noted that the phase of accumulation of these lipids could shift depending on the duration of the cell cycle. The fall in level of PE was followed by a short-term increase (5-10 min). At the same time the level of cardiolipin was observed to be significantly increased.

[The Escherichia coli cell cycle]

This review summarizes present knowledge of the bacterial cell cycle with particular emphasis on Escherichia coli. We discuss data coming from three different types of approaches to the study of cell extension and division: The search for discrete events occurring once per division cycle. It is generally agreed that the initiation and termination of DNA replication and cell septation are discrete events; there is less agreement on the sudden doubling in rate of cell surface extension, murein biosynthesis and the synthesis of membrane proteins and phospholipids. We discuss what is known about the temporal relationship amongst the various cyclic events studied. The search for discrete growth zones in the cell envelope layers. We discuss conflicting reports on the existence of murein growth zones and protein insertion sites in the inner and outer membranes. Elucidation of the mechanism regulating the initiation of DNA replication. The concept of "critical initiation mass" is examined. We review data suggesting that the DNA is attached to the envelope and discuss the role of the latter in the initiation of DNA replication.

Temperature-sensitive catabolite activator protein in Escherichia coli BUG6

BUG6 is a temperature-sensitive cell division mutant which forms filaments at the nonpermissive temperature. Synthesis of the maltose- and galactose-binding protein-dependent transport systems is also temperature sensitive in BUG6. Using operon and protein fusions of the maltose transport genes to lacZ, we observed that the temperature-sensitive control of the maltose transport system in BUG6 occurs at the transcriptional level. By P1-mediated transductions, we found that BUG6 contains two independent temperature-sensitive mutations. One maps between 2 and 3 min on the Escherichia coli linkage map, in close proximity to the fts-envA region. This mutation is responsible for temperature-sensitive cell division. The other mutation maps at 73 min in crp, the structural gene of the catabolite activator protein. The latter could be complemented by a hybrid plasmid carrying the wild-type crp as the only gene on a 0.9-kilobase HindIII-AluI restriction fragment. The mutation in crp alone was found to be responsible for the temperature-sensitive synthesis of the maltose transport system. Although it causes a complete block of transcription of the maltose transport genes at 41 degrees C, this mutation had only a marginal effect on the transcription of the lac operon.

Degraded and stable phosphatidylglycerol in Escherichia coli inner and outer membranes, and recycling of fatty acyl residues

The metabolic fate of membrane phospholipids in exponentially growing Escherichia coli was reexamined by incorporation and chase of labeled precursors: [32P]phosphate, [2-3H]glycerol and 3H-labeled fatty acids. It was found that the well-known turnover of phosphatidylglycerol lasted only about two generation times; after which period, the remaining labeled phosphatidylglycerol, approximately one-third of the total, was stable for at least the subsequent two generation times. The location of the stable phosphatidylglycerol pool remaining after the turnover in the outer and inner membrane was investigated. Both envelopes were found to contain stable phosphatidylglycerol so that the existence of a stable portion cannot be ascribed to its exclusive location in one leaflet. In some experiments, a small loss of labeled phosphatidylethanolamine was also observed, and upon fractionation this was found to occur exclusively in the outer membrane. [32P]Phosphate and [2-3H]glycerol labels of the degraded phospholipids were lost from lipid-soluble material, whereas labeled fatty acid, palmitate or oleate was reincorporated into newly synthesized phosphatidylethanolamine and phosphatidylglycerol, so that total fatty acid label remained constant in (membrane) phospholipid during chase. In view of the amount of glycerol lost, the recycling of the fatty acids under the form of diacylglycerols to phosphatidic acid does not appear to be the predominant pathway of reincorporation. After double labeling with [32P]phosphate and [3H]palmitate, followed by chase, a complete balance sheet of loss and reincorporation of fatty acid, in the three phospholipids, in the two envelopes could be established. Results indicate that fatty acid was reincorporated essentially in the inner membrane phospholipids. Movements of phospholipids and of fatty acids from one membrane to another and in the plane of each layer are discussed in the light of the results.

In vivo intermembrane transfer of phospholipids in the photosynthetic bacterium Rhodopseudomonas sphaeroides

The kinetics of accumulation of phospholipids into the intracytoplasmic membrane of Rhodopseudomonas sphaeroides have been examined. We have previously demonstrated that accumulation of phospholipids in the intracytoplasmic membrane is discontinuous with respect to the cell cycle. In this study we demonstrated a sevenfold increase in the rate of phospholipid incorporation into the intracytoplasmic membrane concurrent with the onset of cell division. Pulse-chase labeling studies revealed that the increase in the rate of phospholipid accumulation into the intracytoplasmic membrane results from the transfer of phospholipid from a site other than the intracytoplasmic membrane, and that the transfer of phospholipid, rather than synthesis of phospholipid, is most likely subject to cell cycle-specific regulation. The rates of synthesis of the individual phospholipid species (phosphatidylethanolamine, phosphatidyglycerol, and an unknown phospholipid) remained constant with respect to one another throughout the cell cycle. Similarly, each of these phospholipid species appeared to be transferred simultaneously to the intracytoplasmic membrane. We also present preliminary kinetic evidence which suggested that phosphatidylethanolamine may be converted to phosphatidycholine within the intracytoplasmic membrane.

Activity of N-acetylmuramoyl-L-alanine amidase in phospholipidic environments

A purified preparation of N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28), a murein hydrolase from Escherichia coli, was found to lose its activity during incubation in the presence of bacterial phospholipid suspensions. Whether it was co-dispersed with the phospholipids or added to sonicated phospholipid suspension, the enzyme was inhibited (or inactivated) from the first minutes of incubation at 37 degree C. As phosphatidylglycerol/cardiolipin ratio of the phospholipid suspension as increased (all other things being equal), a further decrease of amidase activity was observed. The highest losses of activity were found after co-dispersion of the enzyme and the substrate together with the phospholipids, the resulting suspension being formed of larger multilayered vesicles, as revealed by electron microscopy. In these conditions, the effect on enzyme activity was only partially accounted for by the proportion of the enzyme that was entrapped in the vesicles. The entrapment capacity of the enzyme (using a 35S-labelled enzyme preparation) and of the substrate (3H-labelled) by the multilamellar phospholipidic vesicles did not significantly change as a function of their relative content of phosphatidylglycerol and cardiolipin. The possible physiological meaning of the results is discussed is connection with our previous data and with other works related to membranous phospholipid distribution and to septum formation control in bacteria.

Lipid synthesis during the Escherichia coli cell cycle

Lipid synthesis was examined in Escherichia coli cells at different stage of cell division. Exponentially growing cells were pulse-labeled with appropriate isotopes for 0.1 generation time, inactivated, and separated by size on a sucrose gradient. An abrupt increase in the rate of lipid synthesis occurred which was coincident with the initiation of cross walls. In contrast, the rate of protein synthesis during this same interval remained constant, resulting in an increased lipid/protein ratio in dividing cells. No changes in the composition of phospholipid head groups, fatty acids, or phospholipid molecular species were observed in cells at different stages of division. The observed increase in the rate of lipid synthesis may reflect a means by which the activities of membrane-associated enzymes are modulated during cross wall formation.

Use of Escherichia coli operon-fusion strains for the study of glycerol 3-phosphate transport activity

Strains of Escherichia coli K-12 deleted in the native lac operon and bearing both a wild-type glpT operon encoding for sn-glycerol 3-phosphate (G3P) transport and a hybrid operon in which glpT operator and promoter regions are fused to the lacZ gene were constructed. In strains with such a hybrid operon, beta-galactosidase and beta-galactoside permease become inducible by G3P. In these mutants the function and maturation of the glpT-coded proteins should be distinguishable from the level of gene expression, since the beta-galactosidase activity can serve as an index of the latter. With the aid of such mutants, it was shown that: (i) the expressions of the two neighboring operons, glpT and glpA (encoding anaerobic G3P dehydrogenase), are not coordinate; (ii) upon induction, the appearance of the cytoplasmic beta-galactosidase activity preceded that of methyl-beta-D-thiogalactoside transport activity (requiring only a cytoplasmic membrane protein) by about 4 min and that of G3P transport activity (requiring both a cytoplasmic membrane protein and a periplasmic protein) by about 9 min; and (iii) when cells grown at several temperatures from 24 to 42 degrees C were measured for G3P transport activity at 30 degrees C, the activity increased with the growth temperature, indicating that, within the range studied, the rate of transport increases with the fluidity of membrane phospholipids.

Secretion and membrane localization of proteins in Escherichia coli

The envelope of Escherichia coli consists of two distinct membranes, the outer membrane and the cytoplasmic membrane. The space between the two membranes is called the periplasmic space, and each fraction contains its own specific proteins. In this review, it is discussed how proteins are localized in their final locations in the envelope. Proteins localized in the outer membrane and the periplasmic space as well as transmembranous proteins in the cytoplasmic membranes appear to be produced from their precursors which have peptide extensions of about 20 amino acid residues at the amino terminal ends. General features for the peptide extension are deduced from the known sequences of the peptide extensions, and, based on their known properties, a hypothesis (loop model) is proposed to explain the possible functions of the peptide extension during the mechanism of secretion across the cytoplasmic membrane.

Caulobacter cresentus mutant defective in membrane phospholipid synthesis

To study the relationship between phospholipid synthesis and organelle biogenesis in the dimorphic bacterium Caulobacter crescentus, auxotrophs have been isolated which require exogenous glycerol or glycerol 3-phosphate for growth when glucose is used as the carbon source. Upon glycerol deprivation, net phospholipid synthesis ceased immediately in a glycerol 3-phosphate auxotroph which was shown to have levels of biosynthetic sn-glycerol 3-phosphate dehydrogenase (E.C. 1.1.1.8) activity 10 times lower than that of the wild type. In the absence of glycerol, the optical density of the culture continued to increase for the equivalent of one generation, although the cells did not divide. After the equivalent of one generation time, rapid cell death occurred. Cell death also occurred when phospholipid synthesis was inhibited by cerulenin. Although ribonucleic acid and protein syntheses continued at a reduced rate for the equivalent of one generation in mutant strains, a substantial decrease in the rate of deoxyribonucleic acid synthesis occurred immediately upon glycerol deprivation. Revertant strains had wild-type levels of glycerol 3-phosphate dehydrogenase activity and normal rates of phospholipid and macromolecular synthesis.

Phospholipid synthesis during the cell division cycle of Escherichia coli

Stepwise changes in the rate of phosphatidylethanolamine and phospholipid synthesis during the cell division cycle of Escherichia coli B/r were observed. The cell ages at the increases were found to be a function of the growth rate. At each growth rate, the increase occurred around the time new rounds of chromosome replication were inaugurated in the cycle.

Pole cap formation in Escherichia coli following induction of the maltose-binding protein

After induction with maltose, 30--40% of the total protein in the osmotic shock fluid consist of maltose-binding protein while the induction ratio (maltose versus glycerol grown cells) for the amount of binding protein synthesized as well as for maltose transport is in the order of 10. Induction of maltose transport does not occur during all times of the cell cycle, but only shortly before cell division. Electronmicroscopic analysis of cells grown logarithmically on glycerol or maltose revealed in the latter the formation of large pole caps. These pole caps arise from an enlargement of the periplasmic space. Small cells contain one pole cap, large cells contain two. Pulse label studies with strain BUG-6, a mutant that is temperature sensitive for cell division reveal the following: Growth at the non-permissive temperature prevents maltose-binding protein synthesis and formation of new transport capacity. After shifting to the permissive temperature the cells regain both functions. Simultaneously, the newly formed cells exhibit pole caps. We conclude that the induction of maltose-binding protein is responsible for the formation of pole caps. In addition, beside the presence of inducer, cell cycle events occuring during division are necessary for the synthesis of maltose-binding protein.

Phospholipid turnover during the division cycle of Escherichia coli

The turnover of phospholipids in Escherichia coli B/r was analyzed in synchronously growing populations. The turnover of presynthesized phosphatidyl-glycerol and cardiolipin continued at a constant exponential rate throughout the division cycle.

Low-temperature conditional cell division mutants of Escherichia coli

Fifteen low-temperature conditional division mutants of Escherichia coli K-12 was isolated. They grew normally at 39 degrees C but formed filaments at 30 degrees C. All exhibited a coordinated burst of cell division when the filaments were shifted to the permissive temperature (39 degrees C). None of the various agents that stimulate cell division in other mutant systems (salt, sucrose, ethanol, and chloramphenicol) was very effective in restoring colony-forming ability at 25 degrees C or in stimulating cell division in broth. One of these mutants, strain JS10, was found to have an altered cell envelope as evidenced by increased sensitivity to deoxycholate and antibiotics, as well as leakage of ribonulcease I, a periplasmic enzyme. This mutant had normal rates of DNA synthesis, RNA synthesis, and phospholipid synthesis at both the nonpermissive and permissive temperatures. However, strain JS10 required new protein synthesis in the apparent absence of new RNA synthesis for division of filaments at the permissive temperature. The division of lesion in strain JS10 is cotransducible with malA, aroB, and glpD and maps within min 72 to 75 on the E. coli chromosome.

Ribonucleic acid polymerase mutant of Escherichia coli defective in flagella formation

Escherichia coli K-12 mutants that are resistant to bacteriophage chi, defective in motility, and unable to grow at high temperature (42 degrees C) were isolated from among those selected for rifampin resistance at low temperature (30 degrees C) after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Genetic analysis of one such mutant indicated the presence of two mutations that probably affect the beta subunit of ribonucleic acid (RNA) polymerase: one (rif) causing rifampin resistance and the other (Ts-74) conferring resistance to phage chi (and loss of motility) and temperature sensitivity for growth. Observations with an electron microscope revealed that the number of flagella per mutant cell was significantly reduced, suggesting that the Ts-74 mutation somehow affected flagella formation at the permissive temperature. When a mutant culture was transferred from 30 to 42 degrees C, deoxyribonucleic acid synthesis accelerated normally, but RNA or protein synthesis was enhanced relatively little. The rate of synthesis of beta and beta' subunits of RNA polymerase was low even at 30 degrees C and was further reduced at 42 degrees C, in contrast to the parental wild-type strain. Expression of the lactose and other sugar fermentation operons, as well as lysogenization with phage lambda, occurred normally at 30 degrees C, suggesting that the mutation does not cause general shut-off of gene expression regulated by cyclic adenosine 3',5'-monophosphate.

Activity of murein hydrolases in synchronized cultures of Escherichia coli

Murein hydrolase activities were analyzed in synchronized cultures of Escherichia coli B/r. Cell wall-bound murein hydrolase activities, including the penicillin-sensitive endopeptidase, increased discontinuously during the cell cycle and showed maximum activity at a cell age of 30 to 35 min (generation time, 43 min). Maximum activity was observed at the same time that the rate of cell wall synthesis reached its maximum. These oscillations depended on the termination of replication: no increase in hydrolase activity was found if deoxyribonucleic acid synthesis was inhibited at an early time in the life cycle. In contrast, the activity of another murein hydrolase that was not tightly bound to the membrane (transglycosylase) increased exponentially with time, even when deoxyribonucleic acid synthesis was inhibited.

Oscillations in the synthesis of cell wall components in synchronized cultures of Escherichia coli

The rate of cell wall synthesis with respect to both proteins and lipids was determined in synchronized cultures of Escherichia coli B/r. Whereas the rate of total protein synthesis showed an exponential increase with cell age, the rate of incorporation of proteins and lipids into cell wall had a maximum at a cell age of 30 to 35 min, 15 min before cell division. This oscillation was observed in both the cytoplasmic membrane and in the outer membrane of the cell envelope.

Phospholipid composition and phenotypic correction of an envC division mutant of Escherichia coli

The cytoplasmic and outer membranes of a nonconditional chain-forming mutant, Escherichia coli PM61 envC, were separated by sucrose density gradient centrifugation. The phosphatidylglycerol/cardiolipin ratio in both membrane fractions was about one-third as high as in the parental strain P678. The increased level of cardiolipin in PM61 membranes is the result of an alteration of the polyglycerophosphatide cycle. It was found that the turnover rate of phosphatidylglycerol is more rapid in PM61 than in the parental strain but that its cardiolipin turnover is not significantly different. The envC mutation can be corrected phenotypically by increasing the osmolarity of the medium. In the presence of 0.6 M sucrose, the population of PM61 is composed of short rods, and the phosphatidylglycerol/cardiolipin ratio is shifted to that of the parent. The phosphatidylglycerol turns over more slowly, whereas the cardiolipin turns over more rapidly in both strains. Thus, the increase of external osmolarity acts on phospholipid metabolism as well as on an unknown step involved in the mechanism of cell division of the envC mutant.

Septation deficiency and phosphilipid perturbation in Escherichia coli genetically constitutive for the beta oxidation pathway

Mutants of Escherichia coli defective in the regulation of the fatty acids beta oxidation pathway show an ultrastructural deficiency in septum formation at high growth rate. Several independent pairs of parent and mutant strains have been analyzed biochemically. Each parent strain displays a well-defined pattern of cellular phospholipids, which varies with the growth conditions. High ratios of phosphatidylglycerol to cardiolipin characterize fast-growth conditions. None of the mutant strains, although they grow in mass nearly as rapidly as their respective parents, can reach these high ratios. The beta oxidation pathway regulatory mutation leads to an increased turnover of the glycerol moieties of these phospholipids in the inner as well as in the outer cell membrane.

Metabolism of phosphatidylglycerol in cell-free extracts of Escherichia coli

Cell-free extracts from Escherichia coli strain number 9, lacking among other enzymes glycerol kinase, are able to incorporate [2-3H] glycerol into phospholipids. The characteristics of this incorporation indicate that it is not taking place through the regular glycerol phosphate pathway of phospholipid synthesis which occurs when this compound is used as a precursor or even when extracts of E. coli strain 7, having a functional glycerol kinase, are incubated with [2-3H] glycerol. In E. coli strain 9 extracts glycerol is exclusively incorporated into the distal position of phosphatidyl-glycerol while in the other strains the middle position glycerol is partially labelled.

Cell cycle-specific incorporation of lipoprotein into the outer membrane of Escherichia coli

A cell cycle-specific incorporation of free lipoprotein into the outer membrane of Escherichia coli was observed, with a maximal rate of incorporation occuring at the time of septation.

Control of membrane protein synthesis in Bacillus subtilis

In synchronous cultures of Bacillus subtilis 168/S grown on succinate as a sole carbon source (mean generation time 115 min), chromosome initiation occurs at the beginning of the cell cycle but the rate of membrane protein synthesis doubles in mid-cycle more or less coincident with nuclear segregation. In glucose-grown cultures, the doubling in rate of membrane protein synthesis occurs at about the same time as nuclear segregation and DNA initiation at the beginning of the cycle. Control of the rate of membrane synthesis by the chromosome has been demonstrated by inhibiting DNA synthesis using thymine starvation and showing that membrane protein synthesis continues at a constant rate, whereas the rate of cytoplasmic protein synthesis almost doubles. I suggest that the replication of a region at or close to the chromosome terminus is required to allow the doubling in rate of membrane synthesis.

Control of cell length in Bacillus subtilis

During inhibition of deoxyribonucleic acid synthesis in Bacillus subtilis 168 Thy-minus Tryp-minus, the rate of length extension is constant. A nutritional shift-up during thymine starvation causes an acceleration in the linear rate of length extension. During a nutritional shift-up in the presence of thymine, the rate of length extension gradually increases, reaching a new steady state at about 50 min before the new steady-state rate of cell division is reached. The steady-state rates of nuclear division and length extension are reached at approximately the same time. The ratio of average cell length to numbers of nuclei per cell in exponential cultures is constant over a fourfold range of growth rates. These observations are consistent with: (i) surface growth zones which operate at a constant rate of length extension under any one growth condition, but which operate at an absolute rate proportional to the growth rate of the culture, (ii) a doubling in number of growth zones at nuclear segregation, and (iii) a requirement for deoxyribonucleic acid replication for the doubling in a number of sites.

Metabolism of the phosphatidylglycerol molecular species in Escherichia coli

The fractionation, turnover and biosynthesis of the phosphatidylglycerol molecular species of Escherichia coli were studied. Monoacetyldiglycerides derived from phosphatidylglycerol were separated into five subfractions; cis-vaccenyl-palmitoleyl, cis-vaccenyl-cis-vaccenyl, palmityl-palmitoleyl, palmityl-cis-vaccenyl and the disaturated molecular species on a silica gel plate impregnated with silver nitrate. Individual molecular species had different turnover rates. The palmityl-cis-vaccenyl species was metabolized faster than the others. Disaturated species were rather stable. Various phosphatidylglycerol molecular species were synthesized in the presence of sn-glycerol 3-phosphate, palmityl-CoA, palmitoleyl-CoA, cis-vaccenyl-CoA and CTP by the E. coli membrane particulate fraction. When only the proportion of palmityl-CoA among the three acyl-CoAs was increased, the molecular species containing the palmityl residue were increased. Similar results were obtained with the other acyl-CoAs. However, a temperature-sensitive incorporation of unsaturated and saturated fatty acids into phosphatidylglycerol molecular species was observed with no change in the proportions of the three acyl-CoAs, completely reflecting the in vivo unsaturated/saturated ratio.

Intergration of the receptor for bacteriophage lambda in the outer membrane of Escherichia coli: coupling with cell division

Induction of the synthesis of the receptor for phage lambda is obtained by adding maltose and adenosine 3'-5'-cyclic monophosphate to glucose grown cells of Escherichia coli. Bacteria induced for a short period of time were infected with a high multiplicity of phage lambda , and examined under the electron microscope. Only a fraction of the bacteria were seen to have adsorbed a large number of phage particles. The majority of such bacteria had a constriction indicating formation of a septum, and, in this case, the density of adsorbed particles was highest in the vicinity of the constriction. When found on bacteria showing no sign of septum formation, the adsorbed particles were asymmetrically distributed, one pole of the bacteria being more heavily covered with phage particles than the other. Such asymetrically covered bacteria are believed to have originated from cells which divided during the induction period. The results suggest that the receptor for phage lambda, a protein of the outer membrane, is integrated in the cell envelope during the last quarter of each generation and that the integration process is initiated in the vicinity of the forming septum.