An improved Escherichia coli-Rhodococcus shuttle vector and plasmid transformation in Rhodococcus spp. using electroporation

The genetic studies of metabolically diverse Rhodococcus spp. have been hampered by the lack of a system of introducing exogenous DNA. The authors improved an existing Escherichia coli-Rhodococcus shuttle vector (pMVS301) by removing much of the DNA not needed for replication and adding a multicloning site. This improved vector (pBS305) is 7.9 kb in length. Its ability to transform Rhodococcus was tested using electroporation parameters optimized for introduction of pMVS301 into Rhodococcus. Transformation efficiencies as high as 10(5) cfu micrograms-1 DNA were obtained although efficiencies varied depending on the Rhodococcus strain tested. The improved vector pBS305 offers great utility for genetic studies of Rhodococcus because its small size enables movement of large inserts of DNA into Rhodococcus, it has multicloning sites, contains a highly selective thiostrepton marker, and can be replicated in both E. coli and Rhodococcus.

Cloning and expression of the s-triazine hydrolase gene (trzA) from Rhodococcus corallinus and development of Rhodococcus recombinant strains capable of dealkylating and dechlorinating the herbicide atrazine

We used degenerate oligodeoxyribonucleotides derived from the N-terminal sequence of the s-triazine hydrolase from Rhodococcus corallinus NRRL B-15444R in an amplification reaction to isolate a DNA segment containing a 57-bp fragment from the trzA gene. By using the nucleotide sequence of this fragment, a nondegenerate oligodeoxyribonucleotide was synthesized and used to screen a genomic library of R. corallinus DNA for fragments containing trzA. A 5.3-kb PstI fragment containing trzA was cloned, and the nucleotide sequence of a 2,450-bp region containing trzA was determined. No trzA expression was detected in Escherichia coli or several other gram-negative bacteria. The trzA gene was subcloned into a Rhodococcus-E. coli shuttle vector, pBS305, and transformed into several Rhodococcus strains. Expression of trzA was demonstrated in all Rhodococcus transformants. Rhodococcus sp. strain TE1, which possesses the catabolic gene (atrA) for the N-dealkylation of the herbicides atrazine and simazine, was able to dechlorinate the dealkylated metabolites of atrazine and simazine when carrying the trzA gene on a plasmid. A plasmid carrying both atrA and trzA was constructed and transformed into three atrA- and trzA-deficient Rhodococcus strains. Both genes were expressed in the transformants. The s-triazine hydrolase activity of the recombinant strains carrying the trzA plasmid were compared with that of the R. corallinus strain from which it was derived.

Isolation and characterization of an s-ethyl-N,N-dipropylthiocarbamate-degrading Arthrobacter strain and evidence for plasmid-associated s-ethyl-N,N-dipropylthiocarbamate degradation

Arthrobacter sp. strain TE1 isolated from s-ethyl-N,N-dipropylthiocarbamate (EPTC)-exposed soil degraded this herbicide effectively and could grow on EPTC as the sole carbon source. TE1 harboured four plasmids of 65.5, 60, 50.5, and 2.5 megadaltons. Spontaneous mutants unable to degrade EPTC arose at a high frequency, and this was further increased by treatment of the culture with acridine orange or incubation at high temperature. All EPTC degradation-deficient (E-) mutants lacked the 50.5-megadalton plasmid. This plasmid could be transferred from TE1 to E- mutants by conjugation, resulting in the restoration of EPTC-degrading ability to the mutants.

Hydrogenase and ribulose-1, 5-bisphosphate carboxylase activities of Alcaligenes eutrophus ATCC 17706 associated with an indigenous plasmid

Mutants of Alcaligenes eutrophus ATCC 17706 defective in hydrogen uptake (hydrogen oxidation) were isolated following treatment with the plasmid-curing agents Mitomycin C and Acridine orange. These mutants were devoid of hydrogenase and D-ribulose-1, 5-bisphosphate carboxylase activities, but were able to utilize formate. A single-plasmid species was identified in ATCC 17706, which was absent in all Hup− mutants, and was shown to confer hydrogen-uptake proficiency in A. eutrophus. This plasmid, pRMB1, was not self-transmissible, but was conjugative in a strain carrying a self-transmissible plasmid, RK2.

Thymidine incorporation into Rhizobium meliloti

Thymidine is rapidly catabolized to thymine, beta-aminoisobutyric acid, and carbon dioxide by Rhizobium meliloti cells. The incorporation of labelled thymidine into the DNA of R. meliloti cells can be enhanced by the addition of low concentrations (10-20 micrograms/mL) of deoxyadenosine or other nucleosides (adenosine, uridine, guanosine). However, at high concentrations ( greater than 50 micrograms/mL) these compounds inhibit thymidine incorporation. Conditions to obtain highly radioactive DNA of Rhizobium are described.

Uptake and release of tetracycline by cultured carrot cells

The nature of tetracycline uptake by carrot cell suspension cultures is described. Tetracycline enters the cells by diffusion and the intracellular level of the antibiotic increases with the amount added. Exposure of carrot cells to high levels of tetracycline for a limited time (24 hr) followed by the removal of the drug and the resuspension of the cells in drug-free medium does not affect cell growth and has no inhibitory effect on protein synthesis (14C-leucine incorporation).

In vitro plant regeneration from leaf expiants of Lycopersicon esculentum (tomato)

Leaf discs from 15 mutant clones of tomato were tested for their morphogenetic response in Murashige and Skoog medium supplemented with 12 combinations of the growth regulators napthaleneacetic acid (NAA) and benzylaminopurine (BA) and 4 combinations of NAA and zeatin. The results show that either callus, shoots, roots, or shoots and roots can be produced depending upon the hormone concentrations and ratios. Plants were regenerated from 12 of the 15 varieties tested.

Uptake of bacterial DNA by Chlamydomonas reinhardi

Escherichia coli [3H]DNA supplied to vegetative cultures of wild-type (mt+) and CW15 (mt+;mutant lacking the cell wall) Chlamydomonas reinhardi could bind to the cell wall of the wild-type and to the cell membrane of CW15 mutant cells. The extent of this binding decreased with time and was to a large degree (over 90%) DNA-ase-sensitive. Nevertheless, about 0.01% of the bacterial DNA remained irreversibly associated with the cells when they reached stationary phase. The irreversible binding of the donor bacterial DNA to Chlamydomonas cells could be increased by treatment of the cultures with polycations such as DEAE-dextran, poly-L-lysine and poly-L-ornithine. Although the CW15 cells rapidly degraded bacterial DNA in the culture medium wild-type cells showed only a small effect on the molecular weight of the donor DNA. The acid-insoluble radioactivity irreversibly bound to WT (+) cells consisted mainly of oligonucleotides with a small proportion present as less depolymerized donor DNA. No radioactivity, however, was found to be associated with the recipient high molecular weight Chlamydomonas DNA. No labeled donor DNA could be recognized in the cells given bacterial [3H]DNA in early stationary phase. Instead, radioactivity found in Chlamydomonas DNA corresponded to reutilization of [3H]thymine derivatives released as a result of [3H]DNA degradation. No evidence for the integration of detectable amounts of donor DNA sequences into the host cell DNA was obtained.

Effect of uridine on the incorporation of thymine and thymidine in Escherichia coli

Uridine inhibits the incorporation of thymine in Escherichia coli 15T− cells but the duration of this inhibition is dependent upon the initial concentration of uridine and its rate of degradation. Uridine is rapidly degraded to uracil and the completion of this degradation coincides with the release of the inhibitory effect. However, uridine, by preventing the phosphorolysis of thymidine, allows the continued incorporation of the intact molecule at the initial high rate for as long as the concentration of undegraded uridine remains above a certain level. In resuspended 15T− cells, this rate is the same, irrespective of the presence or absence of uridine. The results presented here provide a simple method of controlling DNA synthesis, as represented by thymine incorporation, without the addition of inhibitors or other manipulations of the cell cultures.

Sensitivity to myxin of Escherichia coli treated with ethylenediaminetetraacetic acid

Sensitivity to the antibiotic myxin was significantly increased in Escherichia coli 15T− cells treated with ethylenediaminetetraacetic acid (2 mM) for 5 min. This treatment did not reverse the resistance to myxin in cells of a myxin-resistant strain. Cells of both the susceptible and the resistant strains accumulated myxin intracellularly to the same extent.

Deoxyribonucleic acid degradation and the lethal effect by myxin in Escherichia coli

Exposure of Escherichia coli 15T(-) cells to the antibiotic myxin results in the inhibition of deoxyribonucleic acid (DNA) biosynthesis, degradation of intracellular DNA, and death of the cells. Each of these effects was markedly enhanced when protein synthesis was simultaneously inhibited by chloramphenicol. In the continued presence of chloramphenicol, a brief (1 min) exposure to myxin resulted in a rate of DNA degradation and cell death equivalent to that found in the continued presence of myxin alone. Single-strand breaks were present in the DNA of cells exposed to myxin, but when chloramphenicol was also present the breaks were found much earlier. Degradation of DNA in cells exposed to myxin was found to be distributed randomly in both strands and extended over the genome with no restriction to the vicinity of the replication point. There was no release of DNA from its attachment to the cellular membrane in myxin-exposed cells. The possibility that the chloramphenicol effect is due to the inhibition of repair enzyme synthesis which is stimulated by exposure of the cells to myxin is discussed. These data indicate that the extent of the lethal and metabolic damage to the cells by an exposure to myxin represents the result of competition between damage to and repair of cellular DNA.

Recovery of metabolic activity in Escherichia coli following limited exposure to myxin

Exposure of Escherichia coli to myxin results in the inhibition of DNA synthesis and the cells are killed rapidly. The results presented here indicate that after a short exposure, the removal of myxin allows DNA synthesis to be renewed at the normal rate for a significant period of time before DNA synthesis is again inhibited. This metabolic recovery of DNA synthesis has been shown to be dependent on protein synthesis occurring both during and after exposure to this antibiotic. The protein involved may be one of the DNA-repair enzymes known to be present in these cells. The lethal effect of myxin, therefore, is not due to inhibition of DNA synthesis directly but is probably the result of irreparable damage to the DNA template. This interpretation is supported by the results of similar experiments showing the metabolic recovery of RNA synthesis, which follows a pattern almost identical with that seen with DNA.

Effect of myxin on deoxyribonucleic acid synthesis in Escherichia coli infected with T4 bacteriophage

Exposure of Escherichia coli cells to myxin results in the almost complete inhibition of new deoxyribonucleic acid (DNA) synthesis, extensive degradation of pre-existing intracellular DNA, and a rapid loss of viability in these cells (9). After exposure to myxin for 30 min (<1% survivors and >25% degradation of DNA), infection of these cells by T4 bacteriophage results in the renewal of DNA synthesis at a rate essentially equal to that found in T4-infected cells in the absence of myxin. This DNA was characterized as T4 DNA by hybridization and by hydroxyapatite chromatography. These results suggest that the primary site of action of myxin does not involve the biochemical pathways involved in either the energy metabolism or the biosynthesis of DNA precursors in the uninfected host cell. The yield of infectious T4 particles was reduced when myxin was present during multiplication. This effect may be partly accounted for by the finding that a significant fraction of the T4 DNA synthesized in the presence of myxin is apparently not properly enclosed by the bacteriophage protein coat since it is shown to be degraded by exogenous nuclease.

Mode of action of myxin on Escherichia coli

The effect of the new antibiotic, myxin, on the syntheses of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein in Escherichia coli (strains B and 15T(-)) was examined. Within 7 min of the addition of myxin at 5 mug/ml, the synthesis of new bacterial DNA was almost completely inhibited. This was followed by an extensive degradation of the pre-existing DNA to an acid-soluble form. All of the evidence indicated that the primary effect of the antibiotic was on cellular DNA. The synthesis of RNA was completely inhibited after 15 min of exposure to myxin (5 mug/ml), and the synthesis of protein was markedly reduced after 30 min. There was no measurable breakdown of either RNA or protein in the myxin-treated cells. A marked stimulation of (14)C-uracil incorporation was found in the presence of myxin in 15T(-) cells only. This did not result from an increased rate of RNA synthesis but was due to an increase in the proportion of exogenous uracil, relative to endogenous uracil, incorporated into cellular RNA. This probably reflected a partial inhibition of the biosynthesis of uridine monophosphate from orotate. At 4.5 mug of myxin per ml and with 0.8 x 10(8) cells per ml, 50% of the antibiotic was reduced in 15 min from the biologically active oxidized form to the biologically inactive state. Under these conditions, a maximum of 0.6% (27 mumug/ml) of the myxin was retained in the cells.

Metabolism of amino acids in Agrobacterium tumefaciens. 3. Uptake of L-pro- line

The characteristics of14C-proline uptake by cells of Agrobacterium tumefaciens are described. The results obtained were different from those reported for other bacteria (e.g. Escherichia coli). In addition, significant differences were observed with cells of the non-tumorogenic strain, IIBNV6, as compared to the tumorogenic strain, IIBV7K.Uptake of14C-proline by both strains of cells did not show the specificity known to exist for this amino acid in other microorganisms. A host of unrelated amino acids inhibited proline uptake. Moreover, the inhibitory effects of some amino acids were different in the two strains. Although glutamate and cysteine had no effect on14C-proline uptake in IIBNV6cells, they showed strong inhibition in IIBV7K cells. In addition, cells of the latter strain metabolized proline to a much greater extent than IIBNV6cells.In growing IIBV7K cells, glycine and glutamate suppressed14C-proline uptake and its incorporation into protein. They were also able to displace accumulated14C-proline from the cells. Glycine and leucine, which inhibited proline uptake in IIBNV6cells, showed a similar effect on the displacement of accumulated14C-proline in these cells.Hydroxylamine and Δ′-pyrroline carboxylate suppressed14C-proline uptake and its incorporation into protein in IIBNV6ceils. In IIBV7K cells, on the other hand, Δ′-pyrroline carboxylate had no effect on14C-proline uptake. The incorporation of the label into protein was only slightly reduced. Hydroxylamine in these cells showed a lesser degree of uptake inhibition but a stronger suppression of label incorporation into protein.

Production of radioactive myxin

Uniformly labeled glucose-14C of a high specific activity was supplied to growing cells of a species of Sorangium (strain 3C) under specified conditions. The antibiotic myxin that was synthesized by the cells contained about 10% of the 14C supplied. Because of its specific activity, the purified antibiotic could be used at low concentrations in experiments designed to investigate the site and mechanism of action of this compound with susceptible cells.

Metabolism of amino acids in Agrobacterium tumefaciens. II. Uptake of L-valine by growing cells

Growing cells of Agrobacterium tumefaciens strain IIBV7K (tumorogenic) metabolized14C-valine following its rapid uptake from the medium and released a non-amino metabolite (α-ketoisovaleric acid) into the extracellular fluid. This metabolite was taken up subsequently when the external valine concentration became limiting and was incorporated into protein, probably after conversion to an amino acid, α-Ketoisovaleric acid was not taken up when protein synthesis was blocked, e.g. by chloramphenicol, suggestive of an inducible entry system.α-Ketoisovaleric acid itself inhibited the uptake of14C-valine. It also suppressed the incorporation of label into protein by competition. Hydroxylamine inhibited the incorporation of14C-valine into protein without affecting valine entry into the cells. Glycine inhibited uptake as well as incorporation. Initially, glutamate inhibited14C-valine uptake and incorporation strongly; this was followed after 10 minutes, by rapid and linear entry and incorporation rates of the radioactive substrate.The results are discussed and compared with those from resting cells of A. tumefaciens, details of which were published in a previous paper.

METABOLISM OF AMINO ACIDS IN AGROBACTERIUM TUMEFACIENS: I. UPTAKE OF L-VALINE BY RESTING CELLS

The characteristics of14C-valine uptake by Agrobacterium tumefaciens are described. Highly significant differences were observed with the non-tumorogenic strain IIBNV6and the tumorogenic strain IIBV7K.Resting cells of strain IIBNV6displayed an amino acid uptake pattern, energy requirement, pool saturation, and substrate specificity typical of bacteria (e.g. Escherichia colt) which have been studied previously. In contrast, cells of the strain IIBV7K exhibited an apparent independence from external energy requirements and showed a non-specific competition by structurally unrelated amino acids for14C-valine uptake.In cells of this tumorogenic strain,14C-valine was metabolized after its uptake from the medium, and the metabolic product was effluxed into the extracellular fluid. This product was identified as α-ketoisovaleric acid. Cells of the strain IIBV7K were unable to accumulate this keto acid, although IIBNV6cells took it up readily.Valine uptake by IIBV7K cells was inhibited by a host of structurally unrelated amino acids, which were able to displace the accumulated valine from these cells.The deamination of valine to α-ketoisovaleric acid appears to be associated with a transaminase-type reaction in cells of the strain IIBV7K. Hydroxylamine inhibited the efflux of the product in this strain, whereas in the non-tumorogenic strain it inhibited14C-valine uptake.