Young Sup Chung

Optimal conditions for mutagenesis by ozone in Escherichia coli K12

Abstract A procedure for the quantitative determination of ozone-induced maltose and methionine mutants in Escherichia coli K12 was defined. High yields of induced mutants with over 90% survival have been obtained when washed cells, taken from logarithmic phase of growth, were aerated by a stream of ozone (0.05–1.0 ppm) in buffer at pH 5.0 for 30 to 60 min. It is postulated that ozone itself is probably exerting directly both lethal and mutagenic effects on the cells via a primary effect on the permeability of the cellular membrane.

Induction of deoxyribonucleic acid degradation inEscherichia coli by ozone

Cell survival and deoxyribonucleic acid (DNA) degradation were measured for wild-typeEscherichia coli B251 cells after exposure to different concentrations of ozone. The results show that extensive breakdown of DNA occurs after ozonation and that the extent of ozone-induced DNA degradation generally correlates with the colony-forming ability of the cells.

Résistance à l'ozone chez Escherichia coli

SummaryDifferent strains of E. coli commonly used in genetic studies were exposed to ozone and the results described in this paper indicate that exrA and (lex), but not uvrA genes affect sensitivity to ozone. No relationship between this latter property and the capacity to repair UV-damaged infecting phage (host cell reactivation) was also found. The hypothesis is proposed that the association of ozone sensitivity and X-rays sensitivity in the same mutants may reflect common steps in the mechanism of DNA repair.

Repair of ozone-induced DNA lesions in Escherichia coli B cells

Alkaline sucrose gradient sedimentation indicates that ozone can produce DNA single- and double-strand breaks in wild-type E. coli and ozone-sensitive mutant MQ1844(ozrB). Another type of DNA damage repaired only by the ozrB gene product may also be responsible for the killing effect of ozone on E. coli cells.

Mutagenicity of ozone in different repair-deficient strains of Escherichia coli.

SummaryThe mutagenic activity of ozone was investigated by the isolation of streptomycin-resistant mutants (Sm1) in different strains of Escherichia coli. RecA, lexA, polA and parental strains were ozonated and streptomycin-resistant mutants were scored after a short or long phenotypic delay. Our results suggest that ozone is an active mutagen for forward mutation and that this oxidizing agent could be able to induce mutations via two mechanisms: directly and indirectly by the rec-lex error-prone repair system.

Ozone response in wild type and radiation-sensitive mutants of Saccharomyces cerevisiae

SummaryThe effect of ozone exposure on Saccharomyces cerevisiae was studied. Factors such as ozone concentration, treatment time, media, initial cell concentration and growth phase were shown to influence ozone response in this organism. Logarithmic phase cells were much more sensitive than stationary phase cells to the lethal effect of ozone.The radiation-sensitive mutants rad3, rad6, rad51 and rad52 of S. cerevisiae were exposed, in water, to 50 ppm of ozone for 30 min. On comparing their survival curves, the rad51 and the rad52 mutants showed a greater sensitivity to ozone exposure than the wild type.

Host cell reactivation of ozone-treated T3 bacteriophage by different strains ofEscherichia coli

Host cell reactivation capacity for ozone T3 phage was determined for differentE. coli strains deficient in one or more of the DNA repair mechanisms. The results indicate that DNA polymerase I appears to play a key role in the repair of damage produced on the DNA by ozone while thelexA gene product seems to play a minor one.

Genetic analysis of sul mutants of Escherichia coli B

The sul gene of B/rw (Witkin) and 26 independently isolated sul mutants were examined for their suppression of radiation sensitivity. The suppressed Ion gene was demonstrated by transducing it into a K12 proC recipient. The sul gene of B/rw and all but one of the B/r mutants was found to be linked to a gene controlling azide resistance. Transduction data established the order of markers as leu azi mutT sul. One B/r mutant was found not transducible with azide resistance, sul mutations were found to suppress the capsular polysaccharide production of Ion strains.

Cloning and nucleotide sequence of a new insertion sequence, IS231N, from a non-serotypable strain of Bacillus thuringiensis.

A new IS231 variant, IS231N, has been isolated from an autoagglutinable, non-serotypable strain of B. thuringiensis. IS231N is 1654 bp in length and is delimited by two incomplete 20-bp inverted repeats (IRL and IRR) with two mismatches. No direct repeats (DRs) were found at the right and left borders of IS231N. Surprisingly, IS231N contains three open reading frames (ORFs) that could code for polypeptides of 329 (ORF1), 118 (ORF2), and 17 (ORF3) amino acids, respectively. IS231N lacks the 5th conserved amino acid domain, called C2, owing to the addition of an adenine residue at nucleotide 1319. IS231N shows the highest nucleotide identity (99%) with IS231M, another insertion sequence previously isolated from the same bacterial strain. IS231N, however, shares only 83% amino acid identity with IS231M because of nucleotide substitutions and additions. The ORF1 of IS231N has five fewer amino acids than ORF1 of IS231M. Furthermore, the ORF2-3 putative fusion product in IS231N contains eight fewer amino acids than ORF2 in IS231M. The dendrogram showing the evolutionary relationship between members of the IS231 family and IS231N indicates that IS231N is phylogenetically more closely related to IS231M (83%), followed by IS231F(74%), and is more distant from IS231V and W(46%).

Effect of inhibition of DNA synthesis on u.v. sensitive Bs strains of Escherichia coli.

The effect of nalidixic acid, a specific inhibitor of DNA synthesis, on Escherichia coli strain B ( lon ) and its u.v.-sensitive derivatives is examined. Strain B itself is sensitive to nalidixic acid, whereas its u.v.-resistant derivative B/r is resistant. It is shown that in all exr A strains, in which u.v.-induced filamentation is suppressed, resistance to nalidixic acid is increased. Among exr A strains, Bs4 is exceptionally resistant to nalidixic acid. This is because nalidixic acid kills only growing cells and strain Bs4, a try auxotroph, may grow poorly under the conditions used to test nalidixic acid. The uvr genes of the HCR strains Bs1, Bs8 and Bs12 do not suppress u.v.-induced filamentation nor do they affect the response to nalidixic acid. The uvr gene of strain Bs3 is unusual in increasing the tendency to filament and also sensitivity to nalidixic acid. Strains Bs1, Bs3 and Bs8 are all doubly mutated from strain B, the second mutation (not uvr ) being responsible for their increased resistance to nalidixic acid as well as partially or completely suppressing filamentation. It is concluded that the cell division mechanism of ( lon ) strain B is sensitive to inhibition of DNA synthesis. Mutations which suppress the tendency of strain B to filament reduce its sensitivity to inhibition of DNA synthesis.