CHROMOSOME TRANSFER KINETICS OF SALMONELLA HFR STRAINS

Two pKM101-encoded proteins, the pilus-tip protein TraC and Pep, assemble on the Escherichia coli cell surface as adhesins required for efficient conjugative DNA transfer

Mobile genetic elements (MGEs) encode type IV secretion systems (T4SSs) known as conjugation machines for their transmission between bacterial cells. Conjugation machines are composed of an envelope-spanning translocation channel, and those functioning in Gram-negative species additionally elaborate an extracellular pilus to initiate donor-recipient cell contacts. We report that pKM101, a self-transmissible MGE functioning in the Enterobacteriaceae, has evolved a second target cell attachment mechanism. Two pKM101-encoded proteins, the pilus-tip adhesin TraC and a protein termed Pep, are exported to the cell surface where they interact and also form higher order complexes appearing as distinct foci or patches around the cell envelope. Surface-displayed TraC and Pep are required for an efficient conjugative transfer, 'extracellular complementation' potentially involving intercellular protein transfer, and activation of a Pseudomonas aeruginosa type VI secretion system. Both proteins are also required for bacteriophage PRD1 infection. TraC and Pep are exported across the outer membrane by a mechanism potentially involving the β-barrel assembly machinery. The pKM101 T4SS, thus, deploys alternative routing pathways for the delivery of TraC to the pilus tip or both TraC and Pep to the cell surface. We propose that T4SS-encoded, pilus-independent attachment mechanisms maximize the probability of MGE propagation and might be widespread among this translocation superfamily.

Genetic Transfer of Shigella flexneri Antigens to Escherichia coli K-12

The genes controlling synthesis of Shigella flexneri group- and type-specific antigens were transferred to Escherichia coli K-12 recipients by conjugation with an S. flexneri Hfr. After mating E. coli with an Hfr strain of S. flexneri 2a and selecting for his(+) recombinants, a high proportion of the E. coli hybrids agglutinated in S. flexneri grouping serum. None of these hybrids expressed S. flexneri type-specific antigen II. When an E. coli his(+) hybrid possessing the S. flexneri group antigen was remated with the same Hfr with selection for pro(+) hybrids, a high proportion now expressed the type-specific antigen as well as the previously inherited group antigen. If such crosses were performed in reverse order (i.e., pro(+) followed by his(+) selection), a different pattern of serological behavior was observed. None of the pro(+) hybrids showed the type-specific antigen. Subsequent mating for his(+) resulted in hybrids with both the group- and type-specific antigens. These results show that genes controlling the synthesis of S. flexneri group antigen (linked to the his locus) and type-specific antigen (linked to the pro locus) are widely separated on the chromosome. Expression of the type-specific antigen II depends on the presence of the group antigen.

GENETIC MAPPING OF VI AND SOMATIC ANTIGENIC DETERMINANTS IN SALMONELLA

Johnson, E. M. (Walter Reed Army Institute of Research, Washington, D.C.), Barbara Krauskopf, and L. S. Baron. Genetic mapping of Vi and somatic antigenic determinants in Salmonella. J. Bacteriol. 90:302-308. 1965.-The Vi antigen and somatic antigen 9 were transferred to Salmonella typhimurium recipients by mating with S. typhosa Hfr TD-7, and the genetic determinants of these antigens were located. A gene responsible for Vi antigen expression, ViB was found to be associated with the inlpurA-pyrB linkage group, and the order ViB-inl-purA-pyrB was established. The determinant of somatic antigen 9 was found closely linked to the his gene, and cotransduction of these determinants was accomplished with phage PLT-22. Moreover, all conjugation and transduction hybrids which received the somatic antigen 9 determinant concurrently lost somatic antigen 4. Similarly, S. typhosa hybrids produced by transfer of his and the gene for somatic antigen 4 from S. typhimurium Hfr B2, or by cotransduction of these genes with PLT-22, also lost somatic antigen 9. These results indicated that the genetic determinants of the somatic antigen 9 and 4 are probably allelic. A second Vi antigen determinant, ViA, located near his, was discovered in matings of S. typhimurium Hfr B2 with a Vi-negative S. typhosa recipient. Vi-positive S. typhosa hybrids were obtained from this cross in which neither parent expressed the Vi antigen, indicating that this Vi determinant of S. typhosa is present also in S. typhimurium.

CHARACTERIZATION OF AN HFR STRAIN OF SHIGELLA FLEXNERI

Schneider, Herman (Walter Reed Army Institute of Research, Washington, D.C.), and Stanley Falkow. Characterization of an Hfr strain of Shigella flexneri. J. Bacteriol. 88:682-689. 1964.-A Hfr Shigella flexneri, strain 69, was obtained by terminal marker selection in a cross between Hfr Escherichia coli and S. flexneri. The chromosome of this Hfr Shigella bears gross homology to the E. coli chromosome: it can conjugate with both Shigella and E. coli; its order of gene transmission is the same as E. coli; and interrupted matings show that distance between gene loci is the same as for E. coli. The kinetics of transfer of the pro(+), thr(+) + leu(+), and arg(+) loci by Hfr S. flexneri differ from Hfr E. coli, and may indicate that function of the sex factor, F, derived from E. coli, is modified when integrated into the Shigella chromosome.

Evaluation of two Salmonella typhimurium hybrids as challenge organisms in a system for the assay of typhoid vaccines

A mouse-virulent Salmonella typhimurium hybrid (H42), which expresses the Salmonella typhi Vi antigen in addition to S. typhi O antigens 9 and 12, and a mouse-virulent S. typhimurium hybrid (H1), which expresses only the 9 and 12 antigens of S. typhi, were compared in their behavior as challenge organisms in a system developed to assay the protective capabilities of typhoid vaccines. Swiss-Webster white mice, vaccinated intraperitoneally with live Escherichia coli hybrids expressing the S. typhi O antigens 9 and 12, were significantly protected against death from intraperitoneal challenge with each of the S. typhimurium hybrid strains. Vaccination with an E. coli hybrid expressing the S. typhi Vi antigen in addition to O antigens 9 and 12 was seen to confer no advantage in protection against either S. typhimurium hybrid challenge organism over that obtained by vaccination with an E. coli hybrid expressing only the O antigens of S. typhi. However, a notable difference in the behavior of the two S. typhimurium hybrids was seen in mice vaccinated with the parent of the E. coli hybrid vaccinating strains, E. coli F464, which expresses no surface antigens common to either of these S. typhimurium hybrid challenge organisms. A nonspecific (with respect to the vaccinating strain) protective effect, believed to be associated with Vi antigen expression by the challenge organism, was seen against the challenge with S. typhimurium hybrid H42 after F464 vaccination, whereas no protection was conferred by F464 vaccination against the challenge with Vi-nonexpressing S. typhimurium hybrid H1. Inasmuch as neither S. typhimurium hybrid discriminates between the expression or nonexpression of the Vi antigen in a vaccinating strain, it is concluded that the Vi-nonexpressing S. typhimurium hybrid H1, which more clearly indicates the vaccine-specific protective role of the S. typhi O antigens and does not exhibit the nonspecific protection response of hybrid H42, is the better choice as challenge organism for this vaccine assay system.

Mouse protective capabilities of Escherichia coli hybrids expressing Salmonella typhi antigens

An Escherichia coli hybrid, F1061, expressing Salmonella typhi somatic antigens 9 and 12, and a derivative of this hybrid, E. coli hybrid WR3078, expressing the S. typhi Vi antigen in addition to somatic antigens 9 and 12, were compared with S. typhi Ty2 in experiments to test their ability, as live vaccines, to protect Swiss white mice against death from challenge with a mouse-virulent Salmonella typhimurium hybrid expressing the S. typhi antigens 9, 12, Vi, and d. When the live, vaccinating organisms were administered intraperitoneally, 87.5% of the mice immunized with S. typhi Ty2 survived challenge, as compared with 62.5% of those immunized with E. coli hybrid F1061 and 55% of those inoculated with E. coli hybrid WR3078. When live organisms were administered orally at a dose of 10(9), 67.5% of the mice immunized with S. typhi Ty2 survived challenge as compared with 47.5% of those immunized with E. coli hybrid F1061 and 40% of those administered E. coli hybrid WR3078. Thus, the protection conferred by E. coli hybrid F1061 expressing only the S. typhi somatic antigens, although significant in this system, was inferior to that conferred by S. typhi Ty2 and the addition of the S. typhi Vi antigen to this hybrid (creating E. coli hybrid WR3078) did not enhance that protection.

Genetic basis of Vi antigen expression in Salmonella paratyphi C

Analysis of hybrids formed in a cross between a Salmonella paratyphi C Hfr and an S. typhimurium recipient indicated that the structural genetic determinants of the S. paratyphi C Vi antigen are located closely adjacent to the mel determinant, between this marker and purA. A similar location was indicated for the structural genetic determinants of the S. typhi Vi antigen (the viaB locus) by the results of a mating in which a hybrid S. typhimurium Hfr bearing the S. typhi viaB determinants was used to transfer these genes to an S. typhimurium recipient. Mating experiments with a Vi-antigen-expressing S. typhi Hfr and an S. typhimurium hybrid recipient expressing the Vi antigen of S. paratyphi C yielded no recombinants in which loss of Vi antigen expression occurred, indicating that the chromosomal locus occupied by the genetic determinants of the S. paratyphi C Vi antigen is the same one at which, in S. typhi, the viaB genes reside. Introduction of a mutant S. typhi viaA gene into an S. typhimurium hybrid expressing the Vi antigen, as the consequence of prior receipt of the S. paratyphi C viaB determinants, resulted in that hybrid's loss of Vi antigen expression, demonstrating that the viaA determinant plays a role in Vi antigen expression in S. paratyphi C, as well as in S. typhi. Although the percentages of coinheritance of the viaB and mel determinants in the mating experiments suggested that their linkage is sufficiently close to allow cotransduction by P22, attempts to accomplish this with lysates prepared on S. typhimurium hybrids expressing either S. typhi or S. paratyphi C viaB determinants were not successful.

Genetic mapping of the antigenic determinants of two polysaccharide K antigens, K10 and K54, in Escherichia coli

The genes controlling synthesis of the Escherichia coli acidic polysaccharide capsular antigens K10 and K54 were transferred by conjugation to E. coli strains of other serotypes. The genes concerned with these K antigen determinants showed genetic linkage with the serA locus. We propose to name the K antigen-controlling gene kpsA. The genetic determinants of the two K antigens could also be transferred to enteropathogenic serotypes, even though such strains have never been found in nature with special acidic polysaccharide K antigens. A noncapsulated derivative, K(-), of the K10 strain can transfer the genetic determinant of the K antigen, demonstrating the probable existence of another chromosomal locus involved in the production of such acidic polysaccharide K antigens.

Intraperitoneal mouse virulence of Salmonella typhimurium hybrids expressing somatic antigen 9

Salmonella typhimurium hybrids expressing somatic antigen 9 after mating with either S. typhosa or S. enteritidis Hfr donors did not differ from their S. typhimurium parent with respect to the number of organisms required to produce death in mice inoculated intraperitoneally.

Molecular relationships among the Salmonelleae

Polynucleotide sequence relatedness studies were carried out to determine the extent of divergence present in members of the tribe Salmonelleae and between salmonellae and other enteric bacteria. Typical Salmonella were 85 to 100% related. Two groups of biochemically atypical Salmonella showed somewhat lower binding to typical salmonellae and to each other. Arizona were 70 to 80% related to salmonellae. Two groups of Arizona were detected. These groups correlated with the presence of monophasic or diphasic flagellar antigens. Salmonella and Arizona were no more related to Citrobacter than to Escherichia coli (45-55%). Relatedness of Salmonella and Arizona to other enterobacteria ranged from 20 to 40% with klebsiellae and shigellae, to 20 to 25% with erwiniae, and to less than 20% with edwardsiellae and Proteus mirabilis.

Assay of typhoid vaccines with Salmonella typhosa-Salmonella typhimurium hybrids

Salmonella typhimurium hybrids expressing the S. typhosa antigens 9, d, and Vi were constructed by genetic crosses with an S. typhosa Hfr donor. The hybrids retained the same degree of mouse virulence as their S. typhimurium parent strain, the minimum lethal dose being less than 50 organisms when tested either in C(57) black mice or Swiss white mice. Vaccination of the Swiss white mice with S. typhosa Ty2 vaccines prepared by acetone treatment, alcohol treatment, or heat-killing conferred significant protection against challenge by the hybrid strains but not against their S. typhimurium parent. Both the acetone-treated and alcohol-treated typhoid vaccines were markedly more protective than the heat-killed, phenol-preserved vaccine.

Lytic replication of coliphage lambda in Salmonella typhosa hybrids

Hybrids between Escherichia coli K-12 and Salmonella typhosa which conserved a continuous K-12 chromosomal diploid segment extending from pro through ara to the strA locus were sensitive to plaque formation by wild-type lambda. These partially diploid S. typhosa hybrids could be lysogenized with lambda and subsequently induced to produce infectious phage particles. When the K-12 genes were segregated from a lysogenic S. typhosa hybrid, phage-productive ability was no longer detectable due to loss of a genetic region necessary for vegetative replication of lambda. However, lambda prophage was shown to persist in a quiescent state in the S. typhosa hybrid segregant with phage-productive ability being reactivated after replacement of the essential K-12 lambda replication region. Low-frequency transduction and high-frequency transduction lysates containing the gal(+) genes of S. typhosa were prepared by induction of lambda-lysogenic S. typhosa hybrids indicating that the attlambda site is chromosomally located in S. typhosa in close proximity to the gal locus as in E. coli K-12. After propagation in S. typhosa hybrids, lambda was subject to restriction by E. coli K-12 recipients, thus establishing that S. typhosa does not perform the K-12 modification of lambda deoxyribonucleic acid. Hybrids of S. typhosa, however, did not restrict lambda grown previously on E. coli K-12. The K-12 genetic region required for lambda phage production in S. typhosa was located within min 66 to min 72 on the genetic map of the E. coli chromosome. Transfer of an F-merogenote encompassing the 66 to 72 min E. coli chromosomal region to lambda-insensitive S. typhosa hybrids enabled them to replicate wild-type lambda. The lambda-insensitive S. typhosa hybrid, WR4255, which blocks lambda replication, can be mutagenized to yield mutant strains sensitive to lambdavir and lambdaimm434. These WR4255 mutants remained insensitive to plaque formation by wild-type lambda.

Conservation and transfer of Escherichia coli genetic segments by partial diploid Hfr strains of Salmonella typhosa

Heterozygous, partial diploid hybrids were obtained in a Salmonella typhosa Hfr strain by using it as the recipient in a mating with the Escherichia coli Hfr donor WR2004 (O...proA...leu). Three of these S. typhosa Hfr hybrids were observed to mobilize and transfer the diploid E. coli genes, at high frequencies, to an E. coli recipient. The gradient of transfer frequencies of E. coli markers from these S. typhosa Hfr hybrids was similar to that observed with E. coli Hfr WR2004, from which they were derived. Interrupted matings with one of these S. typhosa Hfr hybrids, designated WR4272, showed the entry times for the proA, thr(-)leu, and argB E. coli diploid markers to be identical to the times obtained for these markers with E. coli Hfr WR2004. Also, the pattern of unselected inheritance of the diploid E. coli markers of S. typhosa Hfr hybrid WR4272 was similar to that observed with the chromosomal markers of E. coli Hfr WR2004. It was concluded that S. typhosa Hfr hybrid WR4272 contains, in addition to its Salmonella genome, a physically continuous E. coli chromosomal segment which is genetically complete from proA to at least the strA locus. The two other S. typhosa Hfr hybrids, on the basis of transmission frequency gradients, appeared to contain a continuous E. coli diploid segment complete from proA through the fuc locus. Other classes of S. typhosa Hfr hybrids, derived from mating with E. coli Hfr WR2010 (O...tna...xyl), were also observed to transfer E. coli genes at high frequency.

Genetic transfer of the Vi antigen from Salmonella typhosa to Escherichia coli

The Vi antigen was expressed in a strain of Escherichia coli after transfer of the viaB locus from a Salmonella typhosa Hfr donor.

Chromosomal location of ribosomal protein cistrons determined by intergeneric bacterial mating

Intergeneric mating between Escherichia coli and Salmonella typhosa was used to locate at least three 30S ribosomal proteins near the streptomycin locus in the region of 54 to 66 min of the E. coli map. This procedure utilizes differences in the electrophoretic patterns of 30S ribosomal protein of the parents. The results show that cistrons for 30S proteins of E. coli can replace those of S. typhosa in the Salmonella genome. Moreover, in a diploid hybrid with a Salmonella endogenote and an E. coli exogenote, both sets of cistrons are expressed.

Polynucleotide sequence relationships among members of Enterobacteriaceae

Polynucleotide relationships were examined among many representatives of the Enterobacteriaceae by means of agar, membrane filter, and hydroxyapatite procedures. The amount of deoxyribonucleic acid (DNA) that reassociated was dependent, especially in interspecific reactions, on the annealing temperature. In only three cases: Escherichia coli-Shigella flexneri, Salmonella typhimurium-S. typhi, and Proteus mirabilis-P. vulgaris, was relative interspecific duplex formation 80% or higher. In most cases interspecies DNA duplex formation was 40% or less of that obtained from intraspecies DNA reassociation reactions. The stability of E. coli-S. flexneri DNA duplexes formed at either 60 or 75 C was virtually identical to that of homologous E. coli DNA duplexes, and the degree of interspecies duplex formation was minimally affected by the temperature increase (86% at 60 C; 77% at 75 C). The thermal stability of DNA duplexes formed at 60 C between DNA from E. coli and DNA from strains of Aerobacter aerogenes, S. typhimurium, S. typhi, and P. mirabilis was about 12 to 14 C below that of reassociated E. coli DNA. At 75 C, the formation of the interspecific DNA duplexes was markedly decreased, but the stability of the DNA able to reassociate at this temperature approximated that of reassociated E. coli DNA. The degree of reassociation and the thermal stability of E. coli-S. flexneri DNA duplexes suggests relatively little evolutionary divergence in these organisms. The other enterobacteria tested, however, have diverged to a point where less than one-half of their DNA can reanneal with E. coli DNA at 60 C and less than 10% reacts at 75 C. The degree of divergence between various enterobacteria does not appear to be uniform along the DNA molecule. Ribosomal ribonucleic acid (RNA)-specific sequences are conserved among most enterobacteria. An examination of messenger RNA relatively specific for the lactose operon suggests that specific chromosomal genes may diverge more or less than the genome as a whole.

Somatic antigen 2 inheritance in Salmonella groups B and D

Somatic (O) antigen 2 of Salmonella paratyphi A replaced somatic antigen 4 of an S. typhimurium recipient as the consequence of mating with an S. paratyphi A var. durazzo Hfr strain. The genetic determinants of these O antigens behaved in this cross as alleles of a common O locus, which is linked to the determinant of histidine biosynthesis, his. By employing phage lysates obtained by growth of P22 on an S. typhimurium hybrid which had received his and O-factor 2 determinants from the S. paratyphi A Hfr, it was possible to cotransduce the his and O-antigen 2 genes to both S. typhimurium and S. typhosa. S. typhimurium transductants which received somatic antigen 2 concurrently lost O-antigen 4, and S. typhosa transductants receiving O-antigen 2, lost their native O-antigen 9. These results indicate that the genetic determinants of O-antigens 2, 4, and 9 occupy the same O locus in S. paratyphi A, S. typhimurium, and S. typhosa, respectively, and are probably allelic.

Behavior of three colicine factors and an R (drug resistance) factor in Hfr crosses in Salmonella typhimurium

An LT2 Hfr strain,his metC gal, was crossed to a multiply marked LT2 F−line. Analysis of recombinant yields, segregation of unselected markers and interrupted matings indicated injection of the Hfr chromosome in the sequence

The introduction into the Hfr of the colicine factorscolI, colE1andcolE2and the R factorR2had little or no effect on its fertility. All four factors were transmitted at low frequency to the F−population, and to recombinants at higher frequencies (colI5–30%,colE130–80%,colE25–30%,R20–9%). Transfer ofcolE1occurred before 20 min., that ofcolE2andcolIlater than 100 min. Segregation data did not reveal close linkage of any factor to any chromosomal locus, but recombinants with a long stretch of donor chromosome were more likely than others to have acquiredcolE2andcolI. Nearly all recombinants andF−cells which acquiredcolIorcolE2acquired both, andcolE1also. Most cells which acquiredR2acquired one or more colicine factors. These plasmid associations can be formally represented by transfer of plasmids, independently of the chromosome, in the sequencecolE1—(colI, colE2)—R2. Phage P22 grown on the Hfr carrying the four plasmids transduced thetet-rtrait ofR2at very low frequency, and thesul-r str-rcharacters, together, at low frequency. Some of each sort of drug-resistance transductant, but no transductants in respect of chromosomal characters, acquiredcolEl or colE2by co-transduction.

Genetic analysis of the ViA-his chromosomal region in Salmonella

Johnson, E. M. (Walter Reed Army Institute of Research, Washington, D.C.), Barbara Krauskopf, and L. S. Baron. Genetic analysis of the ViA-his chromosomal region in Salmonella. J. Bacteriol. 92:1457-1463. 1966.-The relative chromosomal location of the ViA determinant, a gene required for Vi antigen expression in Salmonella typhosa (and present also in S. typhimurium), was examined in S. typhimurium x S. typhosa matings. The position of this gene was determined with respect to the histidine (his) and methionine (metG) biosynthesis markers, and to the genetic determinants of somatic antigens 5 (O-5) and 4 (O-4) of S. typhimurium. The gene order established by analyses of the hybrid classes resulting from the genetic crosses was ViA-O-5-metG-O-4 (his). This order suggests that neither ViA nor O-5 is a member of the complex of functionally related structural genes which constitute the O-4 locus. It allows for the possibility, however, of a functional relationship between the genes of the ViA and O-5 loci.