The β-Galactoside Permease System and the Metabolism of Phospholipids in Escherichia coli

To the Happy Few

I became a microbiologist in post-WWII Japan, working with Toshio Fukasawa on galactose metabolism in Salmonella. We characterized mutants defective in UDP-galactose 4-epimerase, which produced a defective lipopolysaccharide, and this opened doors for me to study lipopolysaccharide biosynthesis, which I pursued in the United States, in the laboratory of Herman Kalckar. After I moved to Berkeley, California, in 1969, I became interested in the function of bacterial outer membranes, a line of work that led to the discovery and characterization of porins as well as the studies on the mycobacterial cell wall. In the early 1990s, it became clear that the outer membrane permeability barrier and the activity of periplasmic β-lactamase are not enough to explain the resistance of some strains to β-lactam antibiotics, and the search for the missing factor led to the discovery of RND family multidrug efflux pumps, subjects that continue to fascinate me to this day.

Enrichment of the bacteriophage PR4 membrane in phosphatidylglycerol is not essential for phage assembly and infectivity

The membrane phospholipids of bacteriophage PR4 grown on wild-type Escherichia coli are markedly enriched in phosphatidylglycerol (PG) relative to host phospholipids. To investigate the role of PG in phage assembly and infectivity, we propagated PR4 on an E. coli mutant defective in PG synthesis. The PG content of PR4 grown on the mutant host accounted for 0.4% of the total viral phospholipids, representing a 90-fold decrease in PG relative to the PG content of phage grown on a wild-type host. Phosphatidylethanolamine and phosphatidic acid, the two major phospholipid species present in these phage preparations, accounted for 88.4 and 9.4% of the total viral phospholipids, respectively. This drastic alteration of the phage phospholipid composition had little or no adverse effect on either the stability or infectivity of the phage. We conclude that the enrichment of the PR4 virion in PG does not reflect an absolute structural requirement of the phage and is not essential for phage infectivity.

DNA-RNA polymerase complexes associated with the membrane from bacteriophage T2- or T4-infected Escherichia coli. I. General properties

Properties of DNA-RNA polymerase complexes, apparently bound to a fraction of the cell membrane of bacteriophage T2- or T4-infected Escherichia coli, are described. Evidence is presented to show that the complexes initiate the asymmetric synthesis of RNA, and release the finished product. The transcription capacity per unit of beta' + beta was 10 times higher at 6 min than at 30 min after infection.

Increased synthesis of phosphatidylcholine by rat lung following premature birth

Pregnant rats were delivered prematurely at 20 days and 21 days gestation (2 and 1 day premature). The survival was 52 +/- 3% at 20 days gestation and 100% at 21 days gestation. [Me-14C]Choline incorporation into phosphatidylcholine increased by 60% during the 3 h of survival after delivery at 20 days gestation. The increase in incorporation occurred during the first hour of survival. [Me-14C]Choline incorporation also increased to a lesser extent following survival at 21 days gestation. The incorporation after 3 h of survival at 20 days and 21 days gestation was similar to that obtained with adult lung slices. The incorporation of [U-14C]glycerol, D-[U-14C]glucose, [1-14C]palmitate and [1,2-14C]ethanolamine did not increase following delivery at either 20 days or 21 days gestation. The incorporation of 33PO4 into phosphatidylcholine increased to the same relative extent as [me-14C]choline incorporation. D-[1-14C]Glucose incorporation into the fatty acid portion of phosphatidylcholine and triacylglycerols and oxidation to 14CO2 decreased during the 3 h of survival. The pattern of D-[U-14C]glucose incorporation following survival at 20 and 21 days gestation is similar to that obtained with adult lung slices. Dexamethasone treatment of mothers at 17 and 18 days gestation caused [Me-14C]choline incorporation to increase to adult values at 20 days gestation but not at 19 days or 21 days. We conclude that an adaptive mechanism exists which produces specific biochemical changes in lung metabolism following premature birth. This mechanism is functional in the rat as early as 2 days prior to normal term.

Phospho-N-acetylmuramoyl-pentapeptide-transferase of Escherichia coli K12. Properties of the membrane-bound and the extracted and partially purified enzyme

Phospho-N-acetylmuramoyl-pentapeptide-transferase (UDP-N-acetyl-muramoyl-L-alanyl-D-gamma-glutamyl-L-lysyl-D-alanyl-D-alanine:undecaprenoid-alcohol-phosphate-phospho-N-acetylmuramoyl-pentapeptide-transferase, EC 2.7.8.13) was solubilized by repeated freezing and thawing of crude envelopes of Escherichia coli K12. The solubilized enzyme was partially purified by gel filtration and ion-exchange chromatography. This preparation contained small amounts of phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol but no endogenous lipid substrate, C55-isoprenyl phosphate, could be detected. Some catalytic properties (exchange reaction) of the solubilized enzyme were compared to those of membrane-bound transferase. The transfer activity of the partially purified transferase was restored by the addition of an aqueous lipid dispersion. All the transferase activity was found to become incorporated into the liposomes. Preincubation of the transferase preparation with phospholipase A2 or D strongly reduce both exchange and transfer activity. This suggests that phospholipids sensitive to phospholipases are necessary for the enzymatic reaction. Different effects of some neutral detergents on the exchange activity were reported.

Lipid composition of sputum from patients with asthma and patients with cystic fibrosis

Lipids from the sputum of patients with asthma and with cystic fibrosis were isolated and characterized. In both cases, lipids constituted approximately 30% of the dry material. Phosphatidlycholine was the most abundant lipid, Significant amounts of phosphatidylethanolamine and phosphatidylglycerol were present. Hexosyl ceramides, sphingomyelin, phosphatidylinositol, lysophosphatidylcholine, and lysophosphatidylethanolamine were present as minor lipid components. Apperciable quantities of neutral lipids were present, of which triglycerides and cholesterol were the main constituents. Phosphatidylcholine, sphingomyelin, and phosphatidylgycerol were highly saturated. Large amounts of phosphatidylcholine containing mostly palmitic acid, particularly in the asthmatic sputum, suggest htat this highly saturated. Large amounts of phosphatidylcholine containing mostly palmitic acid, particularly in the asthmatic sputum, suggests that this highly saturated phospholipid is synthesized in the upper airways for reasons other than its beneficial surface-active properties in the alveoli.

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.

Phospholipids and fatty acids of Neisseria gonorrhoeae

The phospholipids and fatty acids of two strains of Neisseria gonorrhoeae of different penicillin susceptibilities were examined. The phospholipids, which comprise about 8% of the dry weight of the cells, consisted of phosphatidylethanolamine (70%) and phosphatidylglycerol (20%); small amounts of phosphatidylcholine and traces of cardiolipin were also present. Growing and stationary-phase cells were similar in content and composition of phospholipids except for phosphatidylcholine, which increased two- to fivefold in the stationary-phase cells. The fatty acids of the phospholipids were characterized by two major acids, palmitic and a C16:1, with myristic and a C18:1 acid present in smaller amounts. The fatty acids present in purified phospholipid fractions varied considerably in relative proportions from fraction to fraction. No significant difference in the composition of phospholipids from the two strains was evident. Large amounts of beta-hydroxy lauric acid were detected only after saponification of the organisms. Differences in the lipid composition between the gonococcus and other gram-negative bacteria are discussed.

Turnover of phosphatidylglycerol in Escherichia coli

In growing cultures of Escherichia coli, the nonacylated glycerol of phosphatidylglycerol (PG) is labeled more rapidly than is the acylated glycerol. This is, in part, due to a rapid exchange reaction of the nonacylated glycerol. Only some of the PG molecules undergo this reaction while others are stable. Using a mutant unable to make glycerophosphate, we have shown that the nonacylated glycerol of PG can exchange with non-phosphorylated glycerol.

Isolation and characterization of 2-keto-3-deoxyoctonate-lipid A from a heptose-deficient mutant of Escherichia coli

A heptose-deficient mutant of Escherichia coli has been isolated and from it a glycolipid, consisting of lipid A and 2-keto-3-deoxyoctonate (KDO), has been extracted with diisobutylketone-acetic acid-water. Based on beta-hydroxymyristic acid, the extractable glycolipid accounts for a major portion of the total lipid A in this mutant. A glycolipid, purified from the lipid extract by a combination of silicic acid and Sephadex LH-60 chromatography, contains glucosamine, phosphate, KDO, acetyl groups, and fatty acids in the following molar ratios: 1:2:2:1.7:5. These components account for over 80% of the lipid by weight. The fatty acid pattern of the glycolipid is typical of lipid A, the major component being beta-hydroxymyristic acid. The lipid also contains an amino sugar which appears to be 4-amino-4-deoxyarabinose. With the use of an ion-exchange paper chromatographic technique, gram-negative bacteria can be rapidly screened for the presence of this glycolipid. The mutant is believed to have a leaky defect in either biosynthesis of heptose or its incorporation into lipopolysaccharide. The lipopolysaccharide from the mutant contains only about a third as much heptose, glucose, and galactose as the parent CR34, a K-12 derivative. Chemical analysis and phage typing suggest that CR34 contains an incomplete core polysaccharide devoid of glucosamine.

Mechanism of polymyxin B resistance in Proteus mirabilis

The lipids from three types of organisms-a Proteus mirabilis wild type highly resistant to polymyxin B, a polymyxin B-sensitive mutant derived from the wild type, and the wild type grown in the presence of sulfadiazine resulting in phenotypic conversion to polymyxin B sensitivity-were examined to determine the nature of polymyxin B resistance. The phospholipid compositions were nearly identical; each organism contained similar small amounts of N-methyl phosphatidylethanolamine in addition to comparable quantities of phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. the fatty acid compositions were similar in the exponential phase of growth; in the stationary phase, sulfadiazine markedly inhibited the synthesis of cyclopropane fatty acids. Liposomes prepared from the dried lipids of the three types of organisms were extensively and similarly disrupted by the polymyxin. These findings suggest that polymyxin B resistance in P. mirabilis is determined by the cell envelope which prevents access of the antibiotic to the susceptible lipid target sites.

Relationship between phospholipid biosynthesis and the efficiency of the arsenate transport system in yeasts

In studying the possibility that phosphoinositides which formed complexes with arsenic were involved in the arsenate transport system of yeasts, a comparative study of the phospholipid composition and metabolism was carried out both in Saccharomyces carslbergensis and in its arsenate-adapted variant, which showed a deficient inflow of arsenate. It was found that the lipid composition of the two organisms was quite similar, the main classes of phospholipids being phosphatidylcholine, phosphatidylethanolamine, and phosphoinositides. The only difference was a 1.5- to 2-fold increase in the proportion of inositides in the arsenate-adapted cells. When the transport of arsenate became inactivated in the nonadapted yeasts after a 30- to 60-min exposure to 10(-2)m arsenate, an increment of inositides of 29 to 50% over the original level was also detected. A study of the incorporation of radioactivity from uniformly labeled (14)C-maltose and from (32)P-orthophosphate ((32)P(i)) demonstrated a decreased rate of lipid biosynthesis in the arsenate-adapted cells as compared to the normal nonadapted ones. The turnover of the phosphate in phospholipids demonstrated no turnover in phosphatidylcholine and phosphatidylethanolamine, and a slow turnover in phosphoinositides. It could be inferred that a normal rate of phospholipid (phosphoinositides) biosynthesis is necessary to have a normal arsenate uptake and that inositide accumulation impairs both the mechanism responsible for the uptake and accumulation of arsenate and the rate of lipid biosynthesis. No differences were found in the deoxyribonucleic acid or protein content of the two types of cells. Also, the arsenate-adapted cells, once freed of external arsenate, showed an increased uptake of (32)P(i) from low external concentrations of phosphate (10(-6) to 10(-8)m, 10-fold over that observed in AsS cells). These results are indicative of independent behavior in phosphate and arsenate transport systems.