The causes of instability of linkage in transformation of Bacillus subtilis

Transformation in Bacillus subtilis with nitrogen mustard crosslinked DNA. Effect on cotransformation and mutation frequencies

Bacillus subtilis DNA was treated in vitro with nitrogen mustard and the crosslinked molecules were purified, after alkali denaturation, by hydroxyapatite chromatography. When tested for the ability to transform the trpC2-hisB2 segment, these molecules exhibited a decrease in the cotransformation index (r) as compared to native or renatured DNA. The decrease in r was not accompanied by an increase in mutagenicity.

Physiological factors affecting transformation of Azotobacter vinelandii

Cells of Azotobacter vinelandii (ATCC 12837) can be transformed by exogenous deoxyribonucleic acid towards the end of exponential growth. Transformation occurs at very low frequencies when the deoxyribonucleic acid is purified or when the transformation is carried out in liquid medium. Optimal transformation occurs on plates of Burk nitrogen-free glucose medium containing either high phosphate (10 mM) or low calcium (0 to 0.29 mM) content. Higher levels of calcium are inhibitory, whereas magnesium ions are essential for transformation and growth. Extracellular polymer and capsule are increasingly inhibitory to transformation and are most abundant when the calcium content of the medium is high. Transformation is optimal at pH 7.0 to 7.1 and at 30 C, conditions which also coincide with minimal extracellular polymer production. Nonencapsulated strains are excellent transformation recipients. Glycine-induced pleomorphism reduces the transformation frequency and the degree of inhibition is dependent on the phosphate concentration of the medium. Rifampin resistance and shifts from adenine, hypoxanthine, uracil, and nitrogenase auxotrophy to prototrophy can be achieved. Although single marker transfer is always greater than double marker transfer, the data suggest that rifampin resistance is linked to hypoxanthine, adenine and uracil protorophy at intervals of increasing distance. Rifampin resistance did not appear to be linked to nitrogenase.

Kinetic analysis of the products of donor deoxyribonucleate in transformed cells of Bacillus subtilis

This paper describes the major transmutations of donor deoxyribonucleic acid (DNA) after uptake by competent Bacillus subtilis cells. Kinetic experiments confirm that after exposure to competent cells, donor DNA is converted to double-stranded fragments (DSF) which can be isolated as early as 30 s from the beginning of the reaction. At this time, DSF represent the only identifiable product of donor origin. After 1 to 2 min, DSF are converted to deoxyribonuclease-resistant forms, identified as single-stranded DNA fragments (SSF). SSF are intermediates in the transformation process leading to the formation of donor-recipient complex. This component makes its appearance between 2 to 4 min from the beginning of the transformation process. All the donor-recipient complexes found at the end of the reaction can be accounted for quantitatively by the DSF and the SSF found in the initial stages of transformation. A quantitative discussion of the transformation process is included.

Fate of transforming deoxyribonucleic acid after uptake by competent Bacillus subtilis: size and distribution of the integrated donor segments

A series of sheared donor-recipient complex samples were prepared from a competent Bacillus subtilis culture which had been transformed by using (3)H, (2)H-labeled deoxyribonucleic acid. Measurement of the molecular weights and buoyant densities of these samples led to the following conclusions. (i) The average size of the single-stranded donor segment which is integrated is 2.8 x 10(6). (ii) These donor segments are not randomly distributed in the recipient genome, but are clustered in groups, each group containing several discrete donor segments.

Cotransduction and cotransformation of genetic markers in Bacillus subtilis and Bacillus licheniformis

Bacteriophage SP-15, a large generalized transducing phage of Bacillus, was compared with phages PBS-1 and SP-10 for the ability to cotransduce pairs of genetic markers exhibiting different degrees of linkage. When auxotrophs of B. subtilis W-23 were used as recipients, SP-15 and PBS-1 effected a much higher frequency of cotransduction than did SP-10 with markers that were not closely linked. With more closely linked loci, the differences were not as great. SP-15 cotransduced linked markers at a higher mean frequency than PBS-1, suggesting that SP-15 is able to transfer a larger fragment of the Bacillus genome than any phage heretofore described. The frequency of the joint transfer of genetic markers in B. licheniformis was lower via transforming deoxyribonucleic acid than by transduction with phage SP-10. The availability of three procedures for genetic exchange-transduction by SP-15 and SP-10 as well as transformation-each of which reveals a different degree of linkage, makes B. licheniformis 9945A especially amenable to genetic analysis.