Recovery of competence in calcium-limited Azotobacter vinelandii

Azotobacter vinelandii cells required 0.5 mM calcium in the iron-limited competence induction medium. This requirement also was fulfilled by strontium, but not by magnesium. Cells pregrown in competence medium lacking calcium rapidly recovered competence with the addition of 0.5 mM calcium, provided they were suspended in the growth supernatant. A 60,000-dalton glycoprotein (pI 5.10) present in competent or incompetent culture supernatants participated in calcium-mediated competence recovery. Cells grown in calcium-limited medium appeared to have leaky cell envelopes and released a diverse array of proteins into the culture supernatant and into distilled water washes of the cells, seven of which appeared to be more dominant in competent cells. Two distilled water washes of cells grown in calcium-limited medium did not prevent calcium-mediated recovery of competence in the culture supernatant. Four to six distilled water washes removed a competence-specific protein (pI 5.19) and prevented calcium-mediated recovery of competence in the culture supernatant.

Effect of ethylenediaminetetraacetic acid on deoxyribonucleic acid entry and recombination in transformation of a wild-type strain and a rec-1 mutant of Haemophilus influenzae

In transformation of Haemophilus influenzae, donor deoxyribonucleic acid (DNA) enters into competent cells in the presence of ethylenediaminetetraacetic acid (EDTA), which prevents the formation of single stranded regions in the donor DNA that has entered. If after entry of DNA the recipient cells were first incubated at 17 degrees C and then at 37 degrees C in the continuous presence of EDTA, almost no integration occurred. On the other hand, if after entry of DNA the cells were incubated first at 17 degrees C in the absence of EDTA, allowing the generation of single-stranded regions (integration is blocked at this temperature), and then at 37 degrees C in the presence of EDTA, donor-recipient DNA complexes were formed. These results suggest that single-stranded regions are required for integration. Integration to completion was strongly inhibited by EDTA. In a rec-1 mutant of H. influenzae no donor-recipient DNA complexes carrying recombinant-type activity were formed during incubation at 37 degrees C in the absence of EDTA. If rec-1 cells were incubated at 37 degrees C in the presence of EDTA, which strongly inhibited breakdown of DNA, donor-recipient DNA complexes were formed if previously single-stranded regions in the donor DNA that had entered were generated by incubation at 17 degrees C in the absence of EDTA. This suggests that the rec-1 protein protects the initial donor-recipient DNA complex against degradation, so that further steps in the recombination process can proceed.

[Comparative study of chromosome and plasmid transformation in Bacillus subtilis: the effect of lysozyme and polyethylene glycol]

The influence of lysozyme and polyethyleneglycol (PEG) on chromosomal and plasmid transformation was comparatively investigated. Treatment of competent cell culture with low concentrations of lysozyme which do not affect cell viability stimulates both types of transformation. When transforming DNA was treated with definite concentrations of PEG, inhibition of transformation using chromosomal DNA occurred. The similar treatment, however, stimulated transformation by oligomeric forms of plasmid DNA. Possibly, PEG alters the DNA conformation rendering it less sensitive to nuclease degradation. This promotes plasmid transformation but reduces the frequency of transformation by chromosomal DNA, because the changes resulting from nuclease action further DNA integration into the genome of a recipient.

[In vivo restriction of Escherichia coli-transforming DNA by endonuclease R.M.EcoRI]

Transformation of Escherichia coli K-12 for various chromosomal markers was accomplished by using AB1157 recBC+ strain as a recipient. The yield of transformants was reduced 10-fold, as compared with that obtained in JC7623 recBC sbcB recipient. Elimination of transformation has been obtained for arg, pro, his markers in AB1157 (pSA14) harbouring the R.M.EcoRI coding plasmid. Production of restriction endonuclease in this strain did not affect the efficiency of transformation for thr, leu markers. The presence of pSA25 which is isogenic to pSA14 but devoid of R.M.EcoRI genes has been irrelevant to transformation for leu, arg, pro, his, thr markers. Correlation between the restriction of transformed markers in vivo and in vitro is discussed.

DNA binding and deoxyribonuclease activity in Bacillus subtilis during temperature-induced competence development

Rapid development of competence can be induced in cultures of Bacillus subtilis by incubation at 37 degrees C after previous growth at 42 degrees C. This temperature-induced competence was accompanied by an increase in DNA binding capacity and breakdown of donor DNA. Inhibition of protein synthesis prevented the rapid increase of competence. This is probably due to the inhibition of de novo synthesis of a constituent that enables the bacteria to bind DNA.

Polyethyleneglycol-induced transformation of Bacillus subtilis protoplasts by bacterial chromosomal DNA

Bacillus subtilis protoplasts, which in the presence of polyethyleneglycol (PEG) are transformed by plasmid DNA (Chang and Cohen 1979) can also be transformed under these conditions by chromosomal DNA. Transformation in this case occurs at a much lower frequency, not fully accounted for by the heterogeneity of this DNA. Another unexpected feature of the transformation studied, which may explain why it previously went unnoticed, is that DNA concentrations higher than 1--2 microgram/ml decrease the yield of transformants, without showing signs of general toxicity. PEG-induced protoplasts (PIP) transformation for chromosomal markers operates normally with protoplasts prepared from a non-transformable bacterial mutant. The evidence indicates that both native linear and plasmid DNAs must somehow be forced into the cells as a result of PEG action. Denatured chromosomal DNA however is almost inactive in PIP transformation. No competition between chromosomal and plasmid DNAs could be detected, when the DNA tested as inhibitor was in tenfold excess.

The effect of trimethylpsoralen--crosslinks on entry of donor DNA in transformation and transfection of Bacillus subtilis

Transforming chromosomal DNA, irradiated with long-wave UV light in the presence of 4,5',8-trimethylpsoralen (TMP) binds to competent B. subtilis cells as effectively as non-treated DNA, but its transforming activity is strongly reduced. Uptake studies show that the entry of transforming DNA, after some stimulation by short periods of irradiation in the presence of TMP, decreases proportionally with the dose of irradiation. Crosslinking was quantitated by electron microscopy. Since the number of crosslinks increases proportionally with the dose of irradiation, it is suggested that entry of donor DNA is prevented by crosslinks. The inhibition of entry of DNA is paralleled both by decreased breakdown of crosslinked DNA interacting with competent cells, and decreased breakdown by nuclease activity liberated during protoplasting of competent cultures. These data support the model of Lacks et al. (1976) which postulates that a membrane-bound deoxyribonuclease is engaged in the entry of donor DNA into the competent cell. The transforming activity of the chloramphenicol-resistance carrying plasmid pC194, originally obtained from Staphylococcus aureus, is also destroyed by TMP crosslinks. Contrary to chromosomal DNA, its association with the cells is stimulated by long-wave UV irradiation in the presence of TMP, but experiments are presented suggesting that the DNA is still vulnerable to the action of exogenous pancreatic deoxyribonuclease. Transfecting SPP1 DNA is also inactivated by TMP crosslinks. Marker rescue of transfecting DNA containing crosslinks occurs; the extent of rescue of one marker is considerably in excess of that of linked markers.

Restriction and modification in B. subtilis: effects on transformation and transfection with native and single-stranded DNA

The effects of restriction in vivo by competent B. subtilis R cells and in vitro by purified endonuclease BsuR on transformation and transfection with native and denatured DNA were investigated. The results show that transformation by either native, or denatured DNA is not affected by restriction, whereas transfection both with native and denatured SPP1 DNA is severely restricted. In contrast to the results obtained in vivo, the biological activity of native and denatured transforming DNA is destroyed by BsuR in vitro, as is the transfecting activity of native and denatured SPP1 DNA. The sensitivity of denatured DNA, either with mixtures of the complementary strands or with separated single strands alone, is significantly lower than that of native DNA. The results are discussed in the context of possible mechanisms underlying the different responses of transforming and transfecting DNA to in vivo restriction by B. subtilis R cells.

Transformation of Rhodopseudomonas sphaeroides with deoxyribonucleic acid isolated from bacteriophage R phi 6P

The transformation of the photosynthetic bacterium Rhodopseudomonas sphaeroides with the circular genome of the penicillinase-encoding, temperate bacteriophage R phi 6P was demonstrated. The transformation was dependent on the infection of the recipient by another, apparently closely related, temperature bacteriophage, R phi 9. Optimum transformation occurred in the recipient cells already lysogenic for R phi 9 when superinfected with that bacteriophage at multiplicities of infection between 1 and 10 R phi 9 particles per recipient cell.

Influence of bacteriophage PBS1 and phi W-14 deoxyribonucleic acids on homologous deoxyribonucleic acid uptake and transformation in competent Bacillus subtilis

Both bacteriophage PBS1 deoxyribonucleic acid (DNA) (in which all the thymine residues are replaced by uracil) and phage phiW-14 DNA [in which half the thymine residues are replaced by 5-(aminobutylaminomethyl)uracil or 5-putrescinylthymine] exhibit comparable competing abilities for uptake of homologous DNA in a Bacillus subtilis competent system. But, whereas PBS1 DNA leads to a decrease in transformation frequencies compatible with its competing ability for DNA uptake, phiW-14 DNA decreases transformation frequencies by a factor up to eightfold higher. The effect of phiW-14 DNA on transformation frequencies is visible even at a concentration level that does not decrease transforming DNA uptake. No such effect was observed with heterologous DNA containing presumably ionically bound putrescine. Low concentrations of phiW-14 DNA decreased the number of double (nonlinked) transformants more than single transformants. The influence on transformation was abolished when phiW-14 DNA was added 20 min after addition of transforming DNA, i.e., when the recombination process was terminated. The putrescine-containing DNA also decreased retention of trichloroacetic acid-precipitable radioactivity of homologous DNA taken up. We conclude that phiW-14 DNA inhibits some intracellular process(es) at the level of recombination. In addition, there is evidence that phiW-14 DNA, but not heterologous DNA with ionically bound putrescine, binds also to site(s) on the cell surface other than receptors for homologous DNA.

Stimulation of Bacillus subtilis transformation by spermidine

Addition of spermidine in millimolar concentrations to Bacillus subtilis cells curing competence development increases transformability. The spermidine must be added at least 30 min before DNA for maximum stimulation. An incubation period of about 30 minutes is also required for the maximum uptake of labeled spermidine. The amount of DNA initially attached and the rate of DNA uptake are increased to the same extent as transformation. The rate of protein synthesis is also equivalently increased. These observations are consistent with an increase in the number of competent cells in the cell population; this increase is mediated by a spermidine-stimulated protein synthesis.

Influence of some antineoplastic agents on genetic exchange in Bacillus subtilis

The influence of three categories of anti-cancer agents on competence development and on the binding of homologous DNA to cells have been studied in the Bacillus subtilis transformation system. Treatment of cells developing competence with testolactone resulted in a slight enhancement of transforamtion at high doses (50 and 100 micrograms/ml) of the drug, but this process was inhibited at 25 micrograms/ml. DNA binding was unaffected by this drug. DNA-interacting agents (daunomycin, prospidine, peptichemio and mithramycin) usually inhibited DNA-mediated transformation in a higher extent than DNA binding. Antimetabolites of DNA synthesis were also tested: dacarbazine did not greatly inhibit the binding and expression of donor DNA. 5-Fluorouracil appeared to slightly enhance transformation at low levels 1 microgram/ml), although it was inhibited at higher doses.

Superhelical DNA in Streptococcus sanguis: role in recombination in vivo

Competent Streptococcus sanguis treated with non-lethal doses of coumermycin A1 immediately before or after uptake of radioactive transforming DNA were reduced in their capacity to yield transformants. This treatment did not alter bacterial ability to bind DNA in DNase I-resistant form, nor did it prevent the single-stranded donor DNA-recipient protein complexes formed upon uptake at the surface of the bacteria from translocating to chromosomal sites. Inhibition of transformation by heterospecific DNA was greater than that by homospecific DNA. The reduction in transformant yield was not accompanied by any loss of donor counts incorporated into the recipient chromosome, but rather by a loss of genetic activity of incorporated donor material indicating a failure of genetic integration and degradation of donor DNA as a consequence of coumermycin treatment. The inhibitory effect of coumermycin on transformation was associated with in vivo loss of chromosomal DNA superhelicity, The chromosomal DNA remained intact, however, indicative of inhibition of a gyrase-like enzyme responsible for the maintenance of negative supercoiling of the S. sanguis chromosome. Upon treatment with the drug, a coumermycin-resistant mutant strain showed neither loss of chromosomal superhelicity nor any inhibitory effect on genetic integration of donor DNA. The evidence supports the idea that chromosomal superhelicity promotes genetic recombination in vivo.

Transformation and transfection of Pseudomonas aeruginosa: effects of metal ions

The ability of different metal ions to promote transformation of Pseudomonas aeruginosa by deoxyribonucleic acid of the plasmid RP1 was examined. CaCl2, MgCl2, and MnCl2 were found to promote such transformation, although at different frequencies and with the optimum response at different concentrations. Only MgCl2 promoted transfection of P. aeruginosa by the linear deoxyribonucleic acid of phage F116. CaCl2 was demonstrated to allow adsorption and entry into the cell of F116 deoxyribonucleic acid such that it became resistant to exogenous deoxyribonuclease, but phage production occurred only when MgCl2 was provided. Inactivation of linear phage deoxyribonucleic acid taken up in the absence of MgCl2 was observed. The transfection frequencies at various concentrations of MgCl2 were compared, and the optimum response occurred at the concentration which promoted the highest frequency of transformation by RP1 deoxyribonucleic acid.

Identification of different sites of expression for spo loci by transformation of Bacillus subtilis

Asporogenous mutants of Bacillus subtilis were rendered capable of forming heat-resistant spores by transformation with wild-type (spo+) DNA at, or near, the start of sporulation. For several mutants up to about 50% of the colonies derived from heat-resistant spores, formed as a result of the transformation, remained genetically asporogenous (spo). This was thought to indicate that the genome of the mother cell, but not that of the forespore, was transformed to spo+ and that correct expression of the spo locus in the mother cell was sufficient for spore formation. At the end of the process the mother cell was destroyed, leaving a mature heat-resistant spore that was genetically asporogenous. It is concluded that the loci spoIIID, spIVA, spoVB and spoVE are expressed in the mother cell. For one mutant more than 99% of the colonies derived from heat-resistant spores were genetically spo+. It is concluded that the locus involved, spoVA, had to be expressed in the forespore. Thus different sporulation-specific loci are expressed in the mother cell and in the forespore. The loci expressed in the mother cell are expressed in one cell type so that another cell type, the forespore, can develop into a heat-resistant spore. Other unselected donor markers could be introduced into the recipient during transformation provided high concentrations of DNA were used. The frequency of congression was the same for spo survivors as for spo+ survivors. This implies that there was no correlation between the DNA strand into which the selected spo+ and the unselected donor markers integrated.

Enhanced transformability with heterospecific deoxyribonucleic acid upon removal of nascent ribonucleic acid from the Streptococcus sanguis genome

Treatment of Streptococcus sanguis recipient cells with rifampin (RIF) at the time of deoxyribonucleic acid (DNA) addition was an effective means of reducing discrimination, that is, of causing an increase in the number of transformants induced by irreversibly bound heterospecific DNA without significantly changing the number induced by bound homospecific DNA. RIF was unable to reduce discrimination when the recipient cells were RIF resistant due to an altered ribonucleic acid (RNA) polymerase. When recipient cells were treated at the time of DNA addition with concentrations of streptolydigin (STG) as inhibitory of RNA synthesis as RIF, discrimination was not reduced. The kinetics of RNA synthesis inhibition with these inhibitors indicated that, as reported for other bacterial species, RIF inhibited the initiation of transcription by RNA polymerase, whereas STG inhibited the progression of RNA polymerase at any point. Pulse-labeling of RNA immediately before STG addition showed that, if cells were incubated under STG inhibition for 10 to 15 min, their nascent RNA was degraded. Genome-bound RNA polymerase was not released under these conditions. When recipient cells were incubated with STG until nascent RNA was degraded and then exposed to transforming DNA, STG was as effective as RIF in reducing discrimination. The presence of nascent RNA was thereby implicated in the transforming inefficiency of incompletely homologous DNA.

Prolonged incubation in calcium chloride improves the competence of Escherichia coli cells

Escherichia coli cells are 4--6 times more transformable and 20--30 times more competent after 24 h incubation in cold calcium chloride than immediately after calcium chloride treatment. With 24-h-old competent cells we obtained routinely 2 . 10(7) transformants per microgram of pBR322 DNA, and transformed over 20% of viable cells.

Donor deoxyribonucleic acid length and marker effect in pneumococcal transformation

The efficiency of transformation of point mutations depends upon base pair mismatches during the recombination process. For low-efficiency markers, the genetic information carried on the donor deoxyribonucleic acid is preferentially lost. To understand this elimination process, we investigated the effect of the size of donor deoxyribonucleic acid on the relative efficiency of low-efficiency point mutations. The deoxyribonucleic acid was shortened either by mechanical shearing or by restriction enzyme treatments. The results indicate that transformation by low-efficiency markers was not affected by shortening the distance between them and the end of the molecule any more than was transformation by the other markers. Moreover, no lethal event could be detected for either cell or chromosomal marker survival. These data do not exclude the double-strand-break hypothesis that was proposed to explain the loss of genetic information for low-efficiency markers, but they offer no support for it.

[Comparative evaluation of methods of inducing Brucella L forms and a study of their adaptibility in the body of animals]

The action of bicillin-3 on Brucella directly in the body of animals enhances their potential ability to convert into L-forms. One of the factors contributing to the generalization of the infection caused by the L-forms of Brucella and to their prolonged persistance in the body is the presence of an L-transforming agent (in this case, bicillin-3), which indicate that the appearing L-forms of Brucella are obviously antibiotic-dependent.

Features of the damage produced by proflavine on transforming deoxyribonucleic acid

Proflavine formed a complex with transforming deoxyribonucleic acid (DNA) from Haemophilus influenzae, with optimal formation at a ratio of proflavine to DNA of 0.06. The rate of dissociation of the complex by dialysis increased in the order: native, denatured, renatured DNA. The transforming activity of the DNA was reduced by its interaction with proflavine. This inactivation was dependent on the physical state of the DNA, the proflavine concentration, and the temperature. DNA that had been denatured and renatured was most sensitive; native DNA was much less sensitive. The inactivation remained after dialysis and was stable to prolonged storage. It is concluded that the inactivation of transforming DNA by proflavine takes place by a mechanism different from that of DNA-proflavine complex formation.

Proton conductor vs. cold in induction of Ca(2+)-dependent competence in Escherichia coli

In order to elucidate the molecular mechanisms of Ca(2+)-dependent competence in gram-negative bacteria an attempt was made to induce the competence at room temperature in presence of a proton conductor, carbonylcyanide-m-chlorophenylhydrazone (CCCP). Escherichia coli K12 cells treated with Ca2+ at 25 degrees or 37 degrees C in presence of CCCP became permeable for transforming plasmid and transfecting DNAs and DNA-binding antibiotic actinomycin C (AmC) and rubomycin (Rm) at room temperature. The efficiencies of transformation and transfection, however, were by 1-3 orders of magnitude lower compared to cells, treated with Ca2+ at 0 degree C, though both recipients did not differ significantly in their susceptibility to AmC and Rm. Possible mechanisms of Ca2+ action in both recipient systems are discussed in terms of molecular interactions.