Episome-mediated transfer of drug resistance in Enterobacteriaceae. IX. Recombination of an R factor with F

Watanabe, Tsutomu (Keio University, Tokyo, Japan), and Chizuko Ogata. Episome-mediated transfer of drug resistance in Enterobacteriaceae. IX. Recombination of an R factor with F. J. Bacteriol. 91:43-50. 1966.-R factors can be transduced in Salmonella typhimurium with phage P-22, and a majority of the drug-resistant transductants are unable to transfer their drug resistance by cell-to-cell contact, as we have previously reported. Several exceptional types of transductants of S. typhimurium, with the markers of resistance to sulfonamide, streptomycin, and chloramphenicol, were recently obtained by transduction with phage P-22 of a four-drug-resistance R factor carrying the markers of resistance to sulfonamide, streptomycin, chloramphenicol, and tetracycline. They were exceptional in that they had low conjugal transferability of their drug resistance. When one of these exceptional transductants (38R) was transferred to an F(+) strain of Escherichia coli K-12, 38R acquired high transferability in its further transfer. This high transferability was found to be due to the recombination of 38R with F. Transductant 38R was of the fi(+) (fi = fertility inhibition) type, and did not show superinfection immunity against fi(+) and fi(-) R factors. The recombinant 38R.F was genetically very stable and resistant to elimination with acridines. It did not show superinfection immunity against fi(+) and fi(-) R factors, but did show superinfection immunity against F. Further, 38R.F did not restrict a female-specific phage (W-31), unlike wild-type F. F(-) and R(-) segregants were isolated from this recombinant 38R.F, and these segregants exhibited genetic characteristics different from the original R, its transductant 38R, and wild-type F.     

Episome-mediated Transfer of Drug Resistance in Enterobacteriaceae X. Restriction and Modification of Phages by fi R Factors

Watanabe, Tsutomu (Keio University, Tokyo, Japan), Toshiya Takano, Toshihiko Arai, Hiroshi Nishida, and Sachiko Sato. Episome-mediated transfer of drug resistance in Enterobacteriaceae. X. Restriction and modification of phages by fi(-) R factors. J. Bacteriol. 92:477-486. 1966.-An fi(-) R factor, which restricts phages lambda, T1, and T7 without modifying them, was found to restrict and not to modify an F(-)-specific phage, W-31, in Escherichia coli K-12, but not to restrict phage P-22 in Salmonella typhimurium LT-2, whereas other fi(-) R factors restricted and modified P-22 but not W-31; fi(+) R factors did not restrict these phages. Transduction and lysogenization with phages lambda and P-22 were reduced by these fi(-) R factors in K-12 and LT-2, respectively, and the transducing phages lambda and P-22 were modified by these fi(-) R factors. Spontaneous as well as ultraviolet-induced production of phage P-22 and zygotic induction of phage lambda were not significantly affected by any R factor. Injection of the nucleic acids of phages T1 and lambda was not affected by R factors, but the injected phage nucleic acids were rapidly broken down in the bacteria carrying fi(-) R factors. The nucleic acids of the modified phages were not broken down in these bacteria. It was assumed from these results that the mechanism of restriction of phages by fi(-) R factors is due to the breakdown of the injected phage nucleic acids by a deoxyribonuclease(s), presumably located near the cell surface in the cells carrying fi(-) R factors. The deoxyribonuclease(s), formed in the cells carrying the nonmodifying fi(-) R factor, is considered to be different from that synthesized in the cells carrying the modifying fi(-) R factors. It was further shown that the average burst sizes of the unmodified as well as modified phages are slightly reduced by the presence of the fi(-) R factors.     

Transduction of Various R Factors by Phage P1 in Escherichia coli and by Phage P22 in Salmonella typhimurium

R factors fi(+) and fi(-), with various combinations of drug-resistance markers and isolated from independent sources, were transduced by phage P1kc in Escherichia coli and by phage P22 in Salmonella typhimurium. Usually the entire R factor was transduced by P1kc in E. coli, as indicated by the absence of segregation of the drug-resistance markers from their conjugal transferability. In contrast, the patterns of segregation of the drug-resistance markers and their conjugal transferability differed considerably among various R factors after transduction by P22 in S. typhimurium. Transduction frequencies varied among R factors in both transduction systems.     

Covert fi− R Factors in fi− R+ Strains of Bacteria

The presence of an fi(-) sex factor can be detected by propagation of the I-specific phage If1. By use of this method of detection, a high proportion of strains with fi(+) R factors were shown also to carry an fi(-) factor which was frequently a second R factor. In some doubly R(+) strains, the fi(+) and the fi(-) factor were observed to be transferred independently at conjugation.     

Transduction of Pseudomonas aeruginosa with a mutant of bacteriophage E79.

A mutant of the virulent bacteriophage E79 was isolated which mediated generalized transduction in Pseudomonas aeruginosa. Variable recovery of transductants as a result of phage killing was avoided by the use of recipients carrying the IncP-2 plasmid R38, and transduction frequencies of 4 X 10(-6) to 1 X 10(-5) per plaque-forming unit were obtained. Linkage studies have indicated that the coinheritance frequencies are less than would be expected from the published molecular weight of E79 deoxyribonucleic acid (120 X 10(6). By using recipients carrying R38, low-frequency transduction by wild-type E79 and two other virulent phages, F8 and phi 16, was demonstrated.     

Genetic Stability of Various Resistance Factors in Escherichia coli and Salmonella typhimurium

Genetic stability of R factors was studied in Salmonella typhimurium LT-2 and Escherichia coli K-12. It was found that fi(+) R [or R(f)] factors were unstable in LT-2, losing their drug-resistance markers at high frequencies, and were stable in K-12; fi(-) R [or R(i)] factors were stable in both hosts. Both fi(+) and fi(-) R factors were genetically stable also in recombination-deficient mutants of K-12. An fi(+) R factor, which was unstable in S. typhimurium LT-2 wild type, was relatively stable in a recombination-deficient mutant of LT-2. In the spontaneous loss of the drug-resistance markers of fi(+) R factors in LT-2, the markers for sulfanilamide, streptomycin, and chloramphenicol resistance were lost together at high frequencies and the tetracycline marker was retained stably. The remaining drug-resistance markers of the spontaneous segregants of LT-2 were transmissible to K-12 by mixed cultivation, indicating that they were still in the form of R factors.     

Comparisons of F Factors and R Factors: Existence of Independent Regulation Groups in F Factors

The similarity of sex pili mediated by F factors and R(fi(+)) factors and the ability of R(fi(+)) factors to control by repression the functioning of pilus genes encoded by the F factor suggested that F factors and R(fi(+)) factors are closely related. Further comparisons of the episomal properties of F factors and R(fi(+)) factors, however, indicated many differences. F factors contain information for a restriction system for phages phiII and T7. Cells containing R factors are sensitive to these phages. Furthermore, R(fi(+)) factors do not repress the F factor phiII restriction system in cells containing both an R(fi(+)) factor and an F factor. R factors and F factors are heteroimmune episomes. In addition, an R(fi(+)) factor in cells containing both an R factor and an F factor does not fully repress the expression of F-factor immunity to an incoming second F factor. R-factor and F-factor replication systems are not identical. Wild-type F-factor replication genes will complement the mutant F(ts114)lac(+) replication genes in cells containing two F factors. The F(ts114)lac(+) episome is retained when these cells are grown at 42 C; however, cells containing an R(fi(+)) factor and F(ts114)lac(+) lose the F(ts114)lac(+) when grown at 42 C, at the same rate as cells containing only the F(ts114)lac(+). The replication system of the R(fi(+)) factor will not complement the mutant F(ts114)lac(+) replication system.     

Transduction of R Factors by a Proteus mirabilis Bacteriophage

A transducing phage, designated phim, was isolated from a lysogenic strain of Proteus mirabilis and was characterized with respect to its physical and genetic properties. The phage contains double-stranded deoxyribonucleic acid (DNA) with an S(20,w) degrees of 29 which corresponds to a molecular weight of 24 x 10(6) daltons. The base composition of phim DNA was estimated to be 40% guanine plus cytosine on the basis of the buoyant density of the DNA. phim carries out generalized transduction of chromosomal genes in P. mirabilis at a frequency of 5 x 10(-8) to 2 x 10(-6) per adsorbed phage. To obtain R-factor transduction, it was necessary to have a resident R factor in the recipient cells. In these experiments, different combinations of genetically distinguishable R factors were used in the donor and recipient cells. The frequencies of R-factor transduction were 10(-9) to 2 x 10(-8). The transduction of R factors using an R(-) recipient could not be detected. Transductant R factors were usually recombinant between donor and resident R factors. All of the transduced R factors were transferable by conjugation. A plausible explanation for the requirement for a resident R factor in the recipient cells is that phim transduces only a portion of the R-factor genome and therefore requires a resident R factor for genetic recombination. The reason for the low frequencies of R-factor transduction is not known, but some possible interpretations have been discussed.     

Mechanisms of antibiotic resistance determined by resistance-transfer factors

Unowsky, Joel (Northwestern University Medical School, Chicago, Ill.), and Martin Rachmeler. Mechanisms of antibiotic resistance determined by resistance-transfer factors. J. Bacteriol. 92:358-365. 1966.-This study was concerned with the mechanism of expression of drug resistance carried by resistance-transfer (R) factors of two types: fi(-) (negative fertility inhibition) and fi(+) (positive fertility inhibition). The levels of drug resistance determined by R factors used in this study were similar to those reported by other investigators. A new finding was that Escherichia coli carrying the fi(-) episome was resistant to 150 to 200 mug/ml of streptomycin. The growth kinetics of R factor-containing cells were similar in the presence or absence of streptomycin, chloramphenicol, and tetracycline, but a period of adaptation was necessary before cells began exponential growth in the presence of tetracycline. By use of radioactive antibiotics, it was shown that cells containing the fi(-) episome were impermeable to tetracycline and streptomycin, whereas cells containing the fi(+) episome were impermeable only to chloramphenicol. Cell-free extracts from fi(+) and fi(-) cells were sensitive to the antibiotics tested in the polyuridylic acid-stimulated incorporation of phenylalanine into protein.     

Recombination Between a Thermosensitive Kanamycin Resistance Factor and a Nonthermosensitive Multiple-Drug Resistance Factor

The thermosensitive kanamycin (KM) resistance factor, R(KM)(t), and a nonthermosensitive multiple-drug resistance factor, R(100), were simultaneously introduced into Escherichia coli and Salmonella typhimurium. The temperature sensitivity of both R factors remained unchanged as long as they replicated independently. Under certain conditions, however, a new thermosensitive R factor harboring resistance markers for kanamycin, streptomycin (SM), and sulfanilamide (SA) was obtained by recombination between the R(KM)(t) and R(100) factors. R factors carrying resistance markers for KM and SA, or for SM and SA, were obtained from the recombinant R(KM SA SM)(t) by spontaneous segregation. Though the R(100) factor has been known as an fi(+) (positive for F-mediated fertility inhibition of its host) type and it does not restrict any coexisting phages, the thermosensitive recombinants of R(100) with R(KM)(t) and their segregants were found to be fi(-) and to restrict the replication of all T-even phages, as does the R(KM)(t) factor. Double infection immunity was not observed between the R(KM)(t) and R(100) factors.     

Studies on superinfection immunity among transmissible plasmids in Escherichia coli

Superinfection immunity was studied by a method which permits the specific labeling of plasmid DNA following its entry into a recipient cell during conjugation. By measuring the incorporation of [³H]thymine during matings between a donor strain of Escherichia coli K12 carrying the R factor, Rl, and various recipients, we found that the presence in the recipient of a plasmid closely related to R1 (F or R factor 222), or isogenic to it (resistance transfer factor, from Rl), resulted in a reduction of 80 to 90% in the rate of [³H]thymine incorporation, relative to a mating with a plasmid-negative (F ^?) recipient. The DNA present in these recipients after 60 minutes of mating was further examined by neutral sucrose gradient eentrifugation. The DNA in the F⁺ and F ^? recipients sedimented similarly, in two major peaks at 50 S (relaxed circles) and 75 S (supercoiled circles). However, the DNA in the RTF recipient sedimented at rates intermediate between 50 S and 75 S. Pulse-chase experiments revealed that the DNA species seen after 60 minutes of an R1 × RTF mating are normal replicative intermediates which have disappeared by 60 minutes in the R1 × F^? or R1 × F⁺ matings.These data support genetic evidence suggesting that superinfection immunity is due to two distinct effects—entry exclusion and plasmid incompatibility. Thus, F (related to R1 but genetically compatible with it), as well as the incompatible plasmids, 222 and the RTF of R1 itself, when present in the recipient, greatly reduce the total synthesis of newly introduced R1 DNA in the recipient. We interpret this effect as entry exclusion. Incompatibility, manifested by RTF, but not F, further reduces the efficiency of conjugation by slowing the rate at which a newly acquired plasmid is replicated.     

Drug resistance of enteric bacteria. V. High frequency of transduction of R factors with bacteriophage epsilon

Kameda, Mitsuo (Gunma University, Maebashi, Japan), Kenji Harada, Mitsue Suzuki, and Susumu Mitsuhashi. Drug resistance of enteric bacteria. V. High frequency of transduction of R factors with bacteriophage epsilon. J. Bacteriol. 90:1174-1181. 1965.-In the transduction of R factors with phage epsilon(15), a lysate capable of transducing the markers for (TC) or (CM.SM.SA) resistance at high frequency was obtained. The transducing agent is a defective element called epsilon(15)dR(23) which lacks certain functions of phage epsilon(15). After lysogenization with normal epsilon(15) phage and ultraviolet (UV) induction, strains carrying the epsilon(15)dR(23) element produce lysates which have a high frequency of transduction (HFT) on group E(1)Salmonella. Lytic lysates prepared on phage epsilon(15) sensitive strain with the epsilon(15)dR(23) element have a low frequency of transduction (LFT). Lytic growth of phage epsilon(34) on an epsilon(15)dR(23) strain or UV induction of an epsilon(34) lysogenic strain containing epsilon(15)dR(23) results in LFT lysates on group E(2)Salmonella. On UV induction, group E(2)Salmonella (epsilon(15) lysogens) with the epsilon(15)dR(23) element give lysates which are HFT on group E(1)Salmonella but are LFT when tested on group E(2)Salmonella. In all instances, the production of drug-resistant transductants requires infection of the cell with only a single epsilon(15)dR(23) element. It appears that the resistance region of the R factor has replaced that portion of phage genome which is essential for vegetative replication and superinfection immunity. The epsilon(15)dR(23) element does not contain the genetic determinants of the R factor responsible for transmissibility, inhibition of F mating, and interference between two R factors.     

Loss and repair of conjugal fertility and infectivity of the resistance factor and sex factor in Escherichia coli

Hirota, Yukinori (University of Osaka, Osaka, Japan), Toshio Fujii, and Yukinobu Nishimura. Loss and repair of conjugal fertility and infectivity of the resistance factor and sex factor in Escherichia coli. J. Bacteriol. 91:1298-1304. 1966.-The drug-resistance factor, R, and the sex factor, F, have homologous traits, including contagious transmission, mediation of sexuality of the host cell, and autonomous replication in their host bacteria. Cooperation between F and R factors was found with a mutant R factor, which is nontransmissible in F(-) bacteria, becoming transmissible when introduced into bacteria carrying F. Conversely, the chromosome of a sterile male strain carrying the mutant sex factor, F(r), becomes transmissible when an R factor is introduced into the cell. The genetic determinants of R factors have been analyzed by isolation of mutant R factors, by sexual conjugation of the host bacteria, and by transduction of R factors with phage P1kc. The fertility determinant of the R factor, m, is inseparable from the determinant for its infectivity, but can be separated from the loci for autonomous replication of the R factor. R and F thus carry genetic determinants governing the same functions.     

Curing Action of Sodium Dodecyl Sulfate on a Proteus mirabilis R+ Strain

Growth of Proteus mirabilis harboring R100-1 (fi(+)drd str(r)cml(r)tet(r)sul(r)) factors in Penassay broth containing sodium dodecyl sulfate (SDS) leads to the loss of all or part of the genetic elements in high frequencies. In media containing SDS at concentrations as low as 0.03%, both lysis of R(+) cells and elimination of the R factors occur at high frequencies. Appearance of drug-susceptible cells in R(+) cultures occurs during the exponential phase of growth; however, the frequencies of susceptible cells increase substantially after the culture reaches the stationary phase. Reconstruction experiments, coupled with other observations, suggest that the major factor in altering the frequency of drug-susceptible variants is the greater resistance of the variants to the lytic action of SDS. This resistance correlates in most cases with the loss of the transfer functions in the resistance transfer factor.     

Impaired Transduction of R213 and Its Recovery by a Homologous Resident R Factor

Transduction by Plkc of drug-resistance markers of the factor R213 was shown to occur at an exceptionally low frequency (at less than 10(-8) of the input phage), and they could not be transduced by P22. When the recipient cells carried a homologous R factor derived from R213, markers were transduced by Plkc at a normal frequency (at about 10(-5) to 10(-6) of the input phage). Derivative R factors, transducible by Plkc at a normal frequency but being transferred by conjugation at a frequency lower than that of the original R213, were obtained. This type of transductant often segregated R(-) cells. In addition, several transductants contained R factors which were transferred normally by conjugation but were transduced by Plkc at as low a frequency as the original R213. This type of transductant was an effective recipient for transduction by Plkc of R213 when apparently "cured" by acridine treatment. No such effective "cured" recipients were obtained from the transductants with derivatives of R213 transducible at a normal frequency. Two possible interpretations are presented: (i) R213 produces a bacteriocin-like substance upon transduction, or (ii) the genome size of R213 is too large for all of its determinants to be transduced.     

Loss of R Factors Promoted by Bacteriophage M13 and the M13 Carrier State

The infection of different Hfr strains of Escherichia coli bearing derepressed R factors of the fi(+) or fi(-) type can result in the loss of the R factor and the conversion of the infected cells to the R(-) state. This extends earlier observations on the elimination of F' factors by bacteriophage M13 infection. Variability in the efficiency of this conversion can arise because of genetic factors independent of the R factor being eliminated. A fraction of the infected but unconverted R(+) cells were M13 carrier strains. The carrier state had an intracellular basis, and single R(+) cells could maintain the carrier state.     

Transduction of concatemeric plasmids containing the cos site of Lactococcus lactis bacteriophage sk1

Lactococcus lactis bacteriophage sk1 can transduce plasmids containing the phage cos site and surrounding DNA sequences at frequencies as high as 2x10(-3) transductants per PFU. Deletion analysis demonstrated that the presence of phage DNA spanning cos and putative R sites were the most important for efficient plasmid transduction. Inserts of 440 bp containing cos and the R sites were sufficient to induce transduction frequencies of 10(-4) transductants per PFU. The role of the R1 site was investigated by altering 14 of the 19 bases in the site. This resulted in a two-fold decrease in transduction frequency compared to a 26-fold decrease in transduction following deletion of the entire site. It was demonstrated that transducing plasmids were packaged as linear trimeric concatemers commencing at the cos site.     

Molecular Studies on Entry Exclusion in Escherichia coli Minicells

Minicells produced by abnormal cell division in a strain of Escherichia coli (K-12) have been employed here to investigate the phenomenon of "entry exclusion." When purified minicells from strains containing F' or R factors, or both, are mated with radioactive thymidine-labeled Hfr or R(+) donors, the recipient minicells can be conveniently separated from normal-sized donors following mating, and the products of conjugation can be analyzed in the absence of donors and of further growth of the recipients. Transmissible plasmids or episomes are transferred less efficiently to purified minicells derived from strains carrying similar or related elements than to strains without them. Measurement of deoxyribonucleic acid (DNA) degradation and determination of weight-average molecular weights following transfer indicate that degradation of transferred DNA or transfer of smaller pieces cannot account for the comparative reduction in transfer to entry-excluding recipients. Therefore, we conclude that entry exclusion operates to prevent the physical entry of DNA into recipients expressing the exclusion phenotype. The R-produced repressor (product of the drd(+) gene), which represses fertility (i.e., ability to act as donor), reduces exclusion mediated by R or F factor, or both, in matings between strains carrying homologous elements. Furthermore, the data suggest that the presence of the F pilus or F-like R pilus on recipient cells ensures maximum expression of the exclusion phenotype but is not essential for its expression. In contrast to previous suggestions, we found no evidence for a reduction of entry exclusion attributable to the DNA temperature-sensitive chromosomal mutation dnaB(TS).     

Transduction by bacteriophage P22 in nonsmooth mutants of Salmonella typhimurium

The general transducing phage P22 attacks only smooth (S) Salmonella with O antigen 12, determined by the oligosaccharide repeating unit constituting the distal part of the somatic lipopolysaccharide (LPS) side chain; non-S mutants, whose LPS contain few or no O repeating units, appear to be resistant. Auxotrophic non-S mutants of Salmonella typhimurium LT2 were tested as transductional recipients. Some transductants (0.5 to 5% as many as from S recipients) were obtained from most semirough recipients, either of class D (presumed leaky rouA mutants) or of a class due to mutation near his (presumed leaky rouB mutants), and from recipients lacking uridine diphosphogalactose epimerase or phosphomannose isomerase. Transductants were not obtained from several rouA, rouB, "heptose-negative," and glucose-1-transferase mutants, nor from most semirough class C mutants, whose LPS side chains each bear a single O oligosaccharide unit. Most transductants evoked from non-S recipients by temperate (c(+)) phage P22 were nonlysogenic, and virulent P22.c2 phage was about as effective as P22.c(+) in transduction to non-S recipients; probably all P22 transducing particles neither lysogenize nor kill. The extended-host-range mutant P22h gave qualitatively similar results,but evoked 5- to 30-fold more transductants from some non-S recipients than did P22. Probably, the LPS of non-S mutants susceptible to transduction contains a few O-specific oligosaccharide units, conferring a slight ability to adsorb P22 and a greater ability to adsorb P22h.     

Behavior of λ Bacteriophage in a Recombination Deficient Strain of Escherichia coli

The behavior of lambda phage in the Rec(-) strain JC-1569 is compared with that in the Rec(+) strain JC-1557. No difference deemed significant was noted in the adsorption rate, latent period, burst size, frequency of lysogenization, and frequency of vegetative phage recombination. The location of the prophage and its mode of insertion in the Rec(-) lysogen of wild-type lambda (lambda(+)) were inferred to be normal from the results of conjugational crosses. Spontaneous and ultraviolet (UV) irradiation induction of lambda(+) were markedly reduced in the Rec(-) lysogen. On the other hand, thermal induction of a mutant lambda (lambdacI857) lysogen of the Rec(-) strain was not reduced and was only slightly affected by UV irradiation. Phage subject to inhibition by lambda immunity failed to multiply in UV-irradiated cells of the Rec(-) lambda(+) lysogen, whereas those not inhibited by this immunity did multiply. It was concluded that the failure of UV to induce lambda(+) in the Rec(-) lysogen was not due to damage to the prophage, but rather to the inability of the irradiated cells to respond by lifting immunity. Preliminary evidence indicates that a single mutation confers recombination deficiency and the inability to lift immunity after UV irradiation. Possible relationships between recombination and the lifting of immunity are enumerated.