Structure of the O antigen of Escherichia coli K-12 and the sequence of its rfb gene cluster

Escherichia coli K-12 has long been known not to produce an O antigen. We recently identified two independent mutations in different lineages of K-12 which had led to loss of O antigen synthesis (D. Liu and P. R. Reeves, Microbiology 140:49-57, 1994) and constructed a strain with all rfb (O antigen) genes intact which synthesized a variant of O antigen O16, giving cross-reaction with anti-O17 antibody. We determined the structure of this O antigen to be -->2)-beta-D-Galf-(1-->6)-alpha-D-Glcp- (1-->3)-alpha-L-Rhap-(1-->3)-alpha-D-GlcpNAc-(1-->, with an O-acetyl group on C-2 of the rhamnose and a side chain alpha-D-Glcp on C-6 of GlcNAc. O antigen synthesis is rfe dependent, and D-GlcpNAc is the first sugar of the biological repeat unit. We sequenced the rfb (O antigen) gene cluster and found 11 open reading frames. Four rhamnose pathway genes are identified by similarity to those of other strains, the rhamnose transferase gene is identified by assay of its product, and the identities of other genes are predicted with various degrees of confidence. We interpret earlier observations on interaction between the rfb region of Escherichia coli K-12 and those of E. coli O4 and E. coli Flexneri. All K-12 rfb genes were of low G+C content for E. coli. The rhamnose pathway genes were similar in sequence to those of (Shigella) Dysenteriae 1 and Flexneri, but the other genes showed distant or no similarity. We suggest that the K-12 gene cluster is a member of a family of rfb gene clusters, including those of Dysenteriae 1 and Flexneri, which evolved outside E. coli and was acquired by lateral gene transfer.

The effect of naloxone on cerebral blood flow and glucose metabolism in patients with complex partial seizures

We used positron emission tomography with [15O]water and [18F]fluoro-2-deoxyglucose (FDG) to study the effect of naloxone on cerebral blood flow (CBF) and glucose metabolism (LCMRglc) in patients with complex partial seizures. There was no effect on glucose metabolism, but blood flow was reduced 7-12% 45-60 min after infusion of 1 mg/kg naloxone, as was the degree of lateral temporal CBF asymmetry in patients with > 10% baseline hypoperfusion. Endogenous opiates are involved in regulation of human CBF, and possibly in hypoperfusion in epileptic foci. Since [18F]FDG PET measures mean LCMRglc over the tracer uptake and scanning periods, it is inferior to [15O]H2O PET for detecting drug effects which may be time dependent.

Evolution of Salmonella O antigen variation by interspecific gene transfer on a large scale

The O antigen is a bacterial surface polysaccharide made up of repeats of a short oligosaccharide. There are about 60 forms of O antigen in Salmonella, and genetic analysis indicates that these were acquired by interspecific gene transfer.

Comparison of PET measurements of cerebral blood flow and glucose metabolism for the localization of human epileptic foci

We compared the relative sensitivity of two interictal PET techniques, bolus injection of [15O] labeled water for estimation of cerebral blood flow (H2(15)O CBF-PET), and 18F 2-deoxyglucose (18FDG-PET) for cerebral glucose metabolism (CMRglc), and T2-weighted magnetic resonance imaging, in 28 patients with medically intractable complex partial seizures undergoing evaluation for surgery. There were statistically significant associations between lateralization by 18FDG-PET, and MRI, but not H2(15)O CBF-PET, and lateralization of the epileptic focus as defined by scalp-sphenoidal ictal EEG. Fifteen patients had surgery or subdural electrodes. 18FDG-PET was more closely associated with a good outcome than H2(15)O CBF-PET, which, in addition, showed hypoperfusion contralateral to the epileptic temporal lobe in several cases. H2(15)O sensitivity may have been reduced by technical factors, but 18FDG-PET appears to be more specific for localization of epileptic zones.

Felbamate: a clinical trial for complex partial seizures

We performed a randomized, double-blind, three-period cross-over study of felbamate (FBM, 2-phenyl-1,3-propanediol dicarbamate: Carter-Wallace 554) in patients with complex partial seizures. Patients continued carbamazepine (CBZ) throughout the study and were observed in the hospital for the entire trial period. The entry criteria required at least six seizures in a 3-week baseline period (and no more than 1 week with a single seizure) with CBZ alone. Thirty subjects were randomized. Two left the study after randomization, 1 owing to seizure exacerbation, and 1 owing to hyponatremia, which may have been related to CBZ therapy. The daily dosage of 50 mg/kg (maximum 3,000 mg) FBM per day was well tolerated by all 28 patients who completed the study. Only mild adverse experience were observed during the trial. FBM reduced CBZ level (p less than 0.0001; 95% confidence interval -28%, -20%). There was no significant difference in seizure frequency between placebo and FBM periods (one-sided p = 0.172), but when a correction was made for the lower CBZ level noted during FBM periods, the data suggested a strong antiseizure effect of FBM.

The use of a drug resistance cartridge for in vitro insertion and deletion mutagenesis of a cosmid clone

A drug-resistant cartridge was employed in the construction of families of insertion mutants of a cosmid clone. The cartridge contains a cml gene and has identical restriction enzyme sites, EcoRI, BamHI, SalI, and PstI, on both ends. The families of mutants were made by ligation of the cartridge to the cosmid, which was linearized or partially digested, followed by in vitro packaging and transduction. From these families we selected cosmid derivatives which either have a unique BamHI site at a predetermined site in the cosmid or have deletions covering different portions of the original clone. The extent of a large gene cluster cloned into the original cosmid was identified by confirming the gene function in some of the deletion mutants. The possibility for further and various uses of this cartridge is discussed.

Identification and sequence of the gene for abequose synthase, which confers antigenic specificity on group B salmonellae: homology with galactose epimerase

The O antigen of Salmonella group B strains contains the sugar abequose, whereas those from group A and D strains contain paratose or tyvelose in its place. This is the essential difference between these Salmonella groups. Only the final step in the biosynthesis of abequose differs from that of paratose, and the abequose confers on group B strains their specific O4 antigen. The gene, rfbJ, encoding the enzyme abequose synthase for this last specific step has been cloned, identified, and sequenced and has been shown to function in group A and D strains to make them O4+. This one gene thus differentiates group B from group A or group D salmonellae. The enzyme abequose synthase appears to be related to galactose epimerase, and the significance of this is discussed. The rfbJ gene and adjacent DNA is of much lower G+C content than is usual for salmonellae, indicating that the region did not originate in a salmonella but was transferred from outside.

Identification and sequence of rfbS and rfbE, which determine antigenic specificity of group A and group D salmonellae

Salmonella group A, group B, and group D strains have paratose, abequose, and tyvelose, respectively, as the immunodominant sugar in their O antigens, which are otherwise identical; only the final steps differ in the biosynthetic pathways of these sugars. The gene rfbJ from a group B strain, encoding abequose synthase, the final and only unique step in the biosynthesis of CDP-abequose, has been cloned and sequenced (P. Wyk and P. Reeves, J. Bacteriol. 171:5687-5693, 1989). In this study, we locate and sequence rfbS and rfbE from serovars typhi and paratyphi, representative of groups A and D. Gene rfbS is present in both groups and encodes paratose synthase, which carries out a step parallel to that of abequose synthase, but the product is CDP-paratose. The DNA and inferred amino acid sequences are compared with those of rfbJ. We conclude that the genes are homologous, but the divergence is extremely ancient. Gene rfbE encodes CDP-tyvelose epimerase, which converts CDP-paratose to CDP-tyvelose in group D strains; the gene is active in group D strains, and we find it to be present in a mutant form in group A strains. These two genes encode the steps unique to groups A and D and, like rfbJ of group B, are of low G+C content, suggesting transfer from outside of salmonellae. The evolutionary origin of these genes is discussed.

Cloning and nucleotide sequence of the Salmonella typhimurium LT2 gnd gene and its homology with the corresponding sequence of Escherichia coli K12

The complete nucleotide sequence of the Salmonella strain LT2 gnd gene for 6-phosphogluconate dehydrogenase was determined. The gene contains 1404 bases and encodes a 468 amino acid polypeptide, which is the same as for Escherichia coli K12. The DNA sequence shows 14.8% difference between the two and the amino acid sequence 3.6% difference. Changes are mostly in the third codon base and most of the amino acid changes are conservative.

Carbamazepine and its epoxide: relation of plasma levels to toxicity and seizure control

We studied the relation of plasma levels of carbamazepine (CBZ) and carbamazepine 10,11 epoxide (CBZ-E), and their ratio to drug toxicity and seizure control in 7 patients with complex partial seizures. CBZ-E/CBZ increased with increasing CBZ levels and was higher when patients were taking phenytoin or valproic acid. There were weak correlations between CBZ, CBZ-E levels, toxicity scores, and seizure control when patients were taking CBZ alone, but not when other drugs were given as well. There were no significant differences in the correlation with toxicity score or seizure frequency between CBZ, CBZ-E, or their sum. Measurement of CBZ-E levels did not provide additional information useful for monitoring clinical response to CBZ therapy.

Mediation of serum resistance in Salmonella typhimurium by an 11-kilodalton polypeptide encoded by the cryptic plasmid

A cosmid bank of the DNA (including cryptic plasmid DNA) of a virulent strain of Salmonella typhimurium was prepared in Escherichia coli K12, and clones that contained cryptic plasmid DNA were detected by probing. Two such clones expressed a new outer membrane protein of 11 kilodaltons (kDa) and were serum resistant (E. coli K12 is serum sensitive). The gene encoding the 11-kDa protein was subcloned in a 2.1-kilobase fragment and shown to mediate serum resistance in both E. coli K12 and a cryptic plasmid-free (serum-sensitive) strain of S. typhimurium. The cryptic plasmid-free S. typhimurium strain did not express normal lipopolysaccharide, but introduction of the 11-kDa protein gene into the strain rendered the strain serum resistant without restoration of normal lipopolysaccharide synthesis. The 11-kDa protein gene was not sufficient to restore either macrophage resistance or virulence to a cryptic plasmid-free strain of S. typhimurium.

Occupational health and safety: a NSW hospital experience

This paper outlines the experience of the establishment of an Occupational Health and Safety Committee at the Canterbury Hospital and Area Health Service and its achievements over the past two years. As a priority the committee members reviewed and refined safety reporting systems. The committee also considered the need to complement retrospective reporting with a proactive hazard prevention program. A system of departmental inspections was introduced in order to meet this perceived need. Following identification of hazards, education programmes and control strategies were developed to minimise risks. These strategies included some very innovative approaches to perennial problems.

Intermediates in the synthesis of TolC protein include an incomplete peptide stalled at a rare Arg codon

TolC is a minor outer membrane protein of Escherichia coli K 12 and is initially synthesized as a precursor. A distinct intermediate polypeptide of Mr about 46 000 was consistently observed at the initial stages of biosynthesis. The further elongation of this peptide can be blocked by chloramphenicol. We have investigated the cause of the temporary accumulation of the 46 000-Mr intermediate and we postulate that the presence of a rare codon AGA (Arg) at codon 402 of the tolC mRNA halts translating ribosomes owing to a limiting amount of the tRNAArg (AGA) species in the cell. The translation of tolC mRNA can be increased by providing T4 tRNAArg (AGA), encoded on a plasmid.

Molecular characterisation of the Stc- mutation of Escherichia coli K-12

The previously described Stc- (suppressor of TolC) mutation modifies the phenotype of tolC mutants from OmpF- to OmpF+. Restriction mapping of chromosomal DNA from Stc+ and Stc- strains was performed to investigate the nature of the mutation which was shown to be a deletion, upstream of the ompC gene. DNA from the region of the deletion was cloned into pUC18 and a 650-bp PstI-EcoRI fragment was sequenced. The deletion started 49 bp upstream of the AUG start codon of the ompC gene, thus removing part of the ompC promoter and the whole of the micF gene. We suggest that the deletion of micF gives rise to the Stc- phenotype since the effect of micF expression is assumed to reduce ompF expression, and the Stc- phenotype involves increase in ompF expression.

High-level synthesis of the phage lambda outer-membrane protein from the cloned lom gene

A 2.7-kb KpnI-EcoRI fragment carrying the lom gene of bacteriophage lambda has been cloned into plasmid pPR42 and recloned into the SmaI site of pUC9. Large quantities of Lom were seen in outer-membrane (OM) preparations of strains carrying the latter clone and its derivatives. The reading frame of lom was identified as ORF206a. The protein was not demonstrably associated either covalently or non-covalently with the peptidoglycan layer of the cell envelope.

Primary structure of the tolC gene that codes for an outer membrane protein of Escherichia coli K12

We present the nucleotide sequence of the tolC gene of Escherichia coli K12, and the amino acid sequence of the TolC protein (an outer membrane protein) as deduced from it. The mature TolC protein comprises 467 amino acid residues, and, as previously reported (1), a signal sequence of 22 amino acid residues is attached to the N-terminus. The C-terminus of the gene is followed by a stem-loop structure (8 base pair stem, 4 base loop) which may be a rho-independent termination signal. The codon usage of the gene is nonrandom; the major isoaccepting species of tRNA are preferentially utilised, or, among synonomous codons recognized by the same tRNA, those codons are used which can interact better with the anticodon (2,3). In contrast to the codon usage for other outer membrane proteins of E. coli (4) the rare arginine codons AGA and AGG are used once and twice respectively.

The TolC protein of Escherichia coli K12 is synthesised in a precursor form

We examined the biosynthesis of the TolC protein of Escherichia coli K12 in a pulse-chase experiment, followed by immunoprecipitation with anti-TolC antibody and SDS-PAGE of the immunoprecipitate. This showed that TolC protein was originally synthesised in a precursor form (Mr 54 500) which could be chased into the mature form (Mr 52 000). DNA sequencing of a portion of the cloned tolC gene showed that the N-terminus of the mature rotein was preceded by a typical signal sequence of 22 residues (Mr 2542). The initiator Met was preceded by a Shine-Dalgarno sequence, with the correct spacing.

Identification and characterization of the TolC protein, an outer membrane protein from Escherichia coli

We used the cloned tolC gene to identify, locate, and purify its gene product. Strains carrying pPR13 or pPR42 overproduced a cell envelope protein (molecular weight, 52,000). A protein of the same molecular weight was identified in radioactively labeled minicells carrying pPR13; this protein was absent in pPR11-carrying minicells. This protein was the tolC gene product, since pPR11 differed from pPR13 in having a Tn10 insertion in the tolC gene. The protein seen in cell envelopes of whole cells (TolC protein) was found to exist in an aggregated state in the outer membrane; under conditions in which OmpC and OmpF were peptidoglycan associated, TolC protein was not likewise associated. Using these properties, we purified the TolC protein and determined the sequence of twelve amino acids from the amino-terminal end. The location of the TolC protein in the outer membrane was consistent with the proposed function for the tolC gene product as a processing protein in the outer membrane.

A class of ompA mutants of Escherichia coli K12 affected in the interaction of ompA protein and the core region of lipopolysaccharide

A group of ompA mutants of Escherichia coli K12 are described which were sensitive to bacteriophage K3 in a background wild-type for lipopolysaccharide (LPS). With mutant LPS in vivo (lacking some core sugar residues), however, the ompA mutations gave resistance to K3. Outer membrane levels of OmpA protein were normal or near-normal when the mutations resided in either wild-type or mutant LPS backgrounds. Strains in which the mutations occurred in a wild-type LPS background adsorbed K3 phage at the same initial rate and to the same extent as a wild-type strain, but the efficiency of plaquing of the adsorbed K3 was reduced to 25-50% of wild-type levels. Under conditions where a wild-type strain irreversibly adsorbed over 90% of available phage K3 within 3 min, double mutants (ompA mutant, LPS mutant) left 90% of the phage viable after 1 h. The 10% of inactivated phage did not form plaques.

The tolC locus of Escherichia coli affects the expression of three major outer membrane proteins

tolC mutants, which are resistant to colicin E1 and also highly sensitive to detergents and dyes, were shown to lack the OmpF outer membrane protein. There was little effect on transcription as judged by the use of an ompF-lac operon fusion strain, and the tolC effect was probably due to a post-transcriptional effect. The NmpC protein and protein 2 were also tolC dependent.

Molecular cloning of the tolC locus of Escherichia coli K-12 with the use of transposon Tn10

We have cloned the tolC gene of E. coli K-12 into pSF2124 by using transposon Tn10 as the marker to first isolate the relevant DNA fragment. The gene is on a 10.5 kb EcoRI fragment, and Tn5 insertion mutagenesis locates the gene near one end of this EcoRI fragment. An EcoRI-PstI fragment has been subcloned into pBR322 to facilitate further analysis of the gene.

The tsx protein of Escherichia coli can act as a pore for amino acids

The tsx protein is known to be a specific diffusion pathway for nucleosides. The ability of this protein to facilitate the transport of molecules other than nucleosides was examined in strains lacking detectable amounts of porin (ompB mutants). The tsx protein was shown to promote serine, glycine, and phenylalanine transport and to have no effect on either glucose or arginine transport.

High Pressure Liquid Chromatographic Determination of Sulfamethazine or Sulfathiazole and Colorimetric Determination of Sulfathiazole in Feeds: Collaborative Studies

A high pressure liquid chromatographic method for sulfamethazine or sulfathiazole in feeds was studied collaboratively. The sample is extracted in 50% methanol and filtered, and an aliquot is injected into a liquid chromatograph. The column is μBondapak C18, the eluting solvent is acetonitrile–water (20+80), and the detection wavelength is 280 nm. Nine collaborators analyzed 3 different synthetic samples and 2 commercial samples labeled to contain 0.011% sulfamethazine, plus procaine penicillin and chlortetracycline. Average recoveries for the synthetic samples were 102.2% at the 0.005% level, 100.2% at the 0.01% level, and 103.6% at the 0.02% level; per cent standard deviations were 12.7, 10.4, and 8.67, respectively. Average sulfamethazine content of the 2 commercial samples was 77.8 and 82.9% of label with per cent standard deviations of 8.56 and 9.16. The same 2 samples, analyzed according to the official colorimetric procedure by 6 analysts, had an average sulfamethazine content of 81.7 and 89.4% of label with per cent standard deviations of 3.69 and 6.66. Eight collaborators analyzed 3 different synthetic samples and 2 commercial samples labeled to contain 0.011% sulfathiazole, plus procaine penicillin and chlortetracycline. Average recoveries of the synthetic samples were 101.6% at the 0.005% level, 103.0% at the 0.01% level, and 100.4% at the 0.02% level; per cent standard deviations were 9.52, 7.00, and 6.54. Average sulfathiazole content found by 9 collaborators was 0.0103% or 93.4% of label for Sample 1 and 0.0100% or 91.1% of label for Sample 2, with per cent standard deviations of 14.1 and 12.2. Colorimetric assays for sulfathiazole were made according to method 42.172–42.174 for sulfamethazine. Two synthetic samples were analyzed by 7 collaborators. Average recovery was 97.6% at the 0.01% level and 99.8% at the 0.02% level with per cent standard deviations of 5.05 and 8.16. The same 2 commercial samples used for the HPLC study were analyzed by 9 collaborators. Average sulfathiazole found was 86.4 and 87.9% of label with per cent standard deviations of 7.41 and 6.15.

Periplasmic maltose-binding protein confers specificity on the outer membrane maltose pore of Escherichia coli

ompB mutants of Escherichia coli K-12 are markedly deficient in porin in their outer membrane. This results in a decreased rate of uptake for many substrates: the maltose pore (lambda receptor) can in some circumstances, in the absence of the periplasmic maltose-binding protein, compensate for the consequent defects in permeability to lactose, mannitol, glycylglycyl-L-valine, and tri-L-ornithine. It is postulated that the maltose-binding protein associates with the maltose pore and confers on it the specificity for maltose, and that the absence of the maltose-binding protein leaves the pore open and results in enhanced transmembrane diffusion of molecules other than maltose. This paper presents evidence to support this hypothesis.

The concept of bacteriocins

After a short description of the discovery of bacteriocins, especially the colicins in this review the following points are discussed: the classification of colicins especially with the aid of resistant mutants of sensitive indicator strains, the bacteriocin-receptors, the bacteriocin-specificity, and the possible ways of transport of colicins across the outer membrane.

Genetic locus (ompB) affecting a major outer-membrane protein in Escherichia coli K-12

Three multiply colicin-tolerant mutants in Escherichia coli K-12 from the TolIV, TolXIV, and TolXV phenotypic groups, all lacking or having only trace amounts of protein 1, a major outer-membrane protein, were mapped by Hfr crosses, and the position on the chromosome was confirmed by cotransduction with nearby markers. The mutations were located near malQP in the 74-min region of the E. coli chromosome. This locus is designated ompB, and analysis of data from two three-point crosses determined the linear sequence of genes to be aroB-ompB-malQP-glpD.

Outer membrane proteins of Escherichia coli. VI. Protein alteration in bacteriophage-resistant mutants

Protein 1 was shown to be the receptor for phage PA-2 by the observations that the purified protein inactivates the phage, mutants lacking the protein are resistant to the phage, and mutants selected for PA-2 resistance have altered protein. Protein 1 appears as two bands (1a and 1b) on high-resolution polyacrylamide gels. The most abundant classes of mutants (ParI and ParII) selected for PA-2 resistance were found to lack band 1b. The mutations responsible for the ParI and ParII phenotypes were mapped at a locus termed par, which is near nalA on the Escherichia coli chromosome. The cyanogen bromide peptides of proteins 1a and 1b are similar, suggesting that these bands represent modified forms of the same polypeptide. Strains carrying the tolF mutation produce only band 1b. When a par tolF double mutant was constructed, this strain produced only band 1a. These results suggest that genes at the par and tolF loci are involved in modification of protein 1, or regulation of such modification, and are not structural genes for protein 1.

Further characterization of the recipient ability of Escherichia coli K-12 bacteriophage-resistant mutants

We extended the study of Escherichia coli mutants defective in conjugation and showed that the mutants with altered lipopolysaccharide, which are defective as recipients with F-like donors, are also defective with the I-like plasmid R64-11. However, the extent of reduction in recipient ability for I-like donors does not correlate either with the effect on recipient ability for F-like donors or with the degree of alteration to the lipopolysaccharide.

Uptake of ferrienterochelin by Escherichia coli: energy dependent stage of uptake

The uptake of the siderophore-iron complex ferrienterochelin was found to be strongly dependent upon an energized membrane state, as demonstrated by its sensitivity to dinitrophenol, azide, and cyanide. Ferrienterochelin uptake may also be dependent upon phosphate bond energy, as indicated by sensitivity to arsenate and iodoacetic acid. Although the adenosine triphosphatase does not appear to be involved in this energy coupling mechanism, ferrienterochelin uptake was shown to be less dependent upon phosphate bond energy than was glutamine uptake. Sensitivity of ferrienterochelin uptake to osmotic shock was shown to be due to the release of a ferrienterochelin binding compound located in the outer membrane of the cells and probably identical to the colicin B receptor protein.

Comparison of colicins B-K260 and D-CA23: purification and characterization of the colicins and examination of colicin immunity in the producing strains

Colicins B-K260 and D-CA23 were purified by ammonium sulfate precipitation, gel filtration, and ion-exchange chromatography and were compared with respect to a number of physical and chemical properties. Both colicins were shown to be proteins and were found to have similar molecular weights, isoelectric points and amino acid compositions. The two colicins also have substantial antigenic similarities but are distinguished by the presence of non-cross-reacting antigens and by differences in stability and in sensitivity to heat and reducing conditions. In addition, strains of Escherichia coli K-12 producing colicins B-K260 and D-CA23 are not cross-immune. The similarities noted between the two colicins are compatible with their use of a common cell surface receptor while having different modes of action.

Outer membrane of Escherichia coli K-12: isolation of mutants with altered protein 3A by using host range mutants of bacteriophage K3

A series of mutants has been isolated with alterations to protein 3A of the outer membrane. These mutations map at the previously described con locus as shown by cotransduction with pyrD. Most of them do not have detectable levels of protein 3A but are thought to have low levels of altered protein. These mutants have been detected by screening con mutants, isolated as resistant to bacteriophage K3, for their ability to plaque host range mutants of this bacteriophage. These host range phage mutants have activity spectra on the various con mutants that enable the bacterial mutants to be arranged in an order of increasing resistance to the host range phage mutants, from mutants sensitive to all host range phage to those sensitive to only one class. Likewise, the phage can be arragned in an order of increasing ability to plaque on the con mutants. Some of the mutants resemble the previously described con mutants in being tolerant to colicins K and L, and others resemble them in being highly defective as recipients with the F factor. These properties vary independently, suggesting that protein 3A can be modified to independently affect the three properties of bacteriophage receptor function, involvement in colicin sensitivity, and involvement in conjugation.

Outer membrane of Escherichia coli K-12: differentiation of proteins 3A and 3B on acrylamide gels and further characterization of con (tolG) mutants

Two classes of mutants, con and tolG, that appeared to be very similar in a number of respects have been shown to be identical and cotransducible with pyrD. By diethylaminoethyl-cellulose chromatography of the outer membranes, we have shown that the mutants are missing only protein 3A and retain protein 3B. Using con mutants, we were thus able to identify protein 3B on the pH 7.2 gel system of Maizel where it runs separately from protein 3A if unheated samples are used. tolG mutants were shown to be identical to con mutants in being conjugation defective with most F-like plasmid donors but not with I-like plasmid donors, and in their resistance pattern to bacteriophages and colicins. During the course of this study, it was observed that the bacteriocin produced by Serratia marcescenc JF246 was identical in its activity spectrum to colicin L-398 and is now considered to be a colicin of type L.

Effect of tra mutations on F factor-specified immunity to lethal zygosis

Hfr, F+, and F-prime cells are, unlike F- cells, insensitive to an excess of Hfr donor cells, indicating that there is an F factor mediated immunity to lethal zygosis (I1z). Results with Flac episomes carrying traJ, traS or various polar mutations in the tra region indicate that this immunity is independent of surface exclusion, of traJ control, and of all known genes within the tra operon. However, analysis of a series of strains with deletions in the F factor, extending from the right into the tra region, suggests that a gene for immunity to lethal zygosis is located within the tra region. We therefore conclude that I1z is genetically complex, and present a hypothesis to account for these results.

Lipopolysaccharide-deficient, bacteriophage-resistant mutants of Escherichia coli K-12

Bacteriophage-resistant mutants isolated and classified in a previous study were examined for alterations in their lipopolysaccharide (LPS) composition, and properties likely to be affected by alterations in LPS composition were studied. It was found that many of the mutants of the Ktw (K2-resistance), Ttk (T2, T4, or K19 resistance), Bar (bacteriophage), Wrm (wide-range mutants), and miscellaneous resistance groups were altered in their response to a series of antibiotics and to two LPS-specific bacteriophages, C21 and U3. Furthermore, many of the bacteriophages to which these mutants were resistant adsorbed to LPS preparations. By direct sugar analysis of the mutant LPS preparations, it was shown that the mutants fitted into six distinct classes, which are readily derived from LPS core with a structure resembling that of Salmonella or Escherichia coli O100. A number of the mutants were shown to map between pyrE and mtl, which has been previously shown to be the site of a cluster of rfa genes in both Salmonella and E. coli. Outer membrane protein composition was studied in the above mutants using polyacrylamide gel electrophoresis. Some strains were shown to have alterations in the amount of major proteins. The nature of the bacteriophage receptors involved and the alterations leading to resistance are discussed.