GENETIC INSTABILITY WITH EPISOME-MEDIATED TRANSFER IN ESCHERICHIA COLI

Abstract

Gundersen, Wenche B. (Oslo University, Oslo. Norway), Kaare Jyssum, and Sverre Lie . Genetic instability with episome-mediated transfer in Escherichia coli . J. Bacteriol. 83: 616–623. 1962.—Hospital strains of Escherichia coli have been simultaneously screened for an increased mutation rate to streptomycin (Sm) resistance and to auxotrophy. Two strains were found with an increased mutation rate to Sm, but with no more than normal mutation rates in other loci tested. These loci included threonine, histidine, methionine, isoleucine-valine, resistance to tetracycline, and resistance to chloramphenicol. The genetic determinant of the new type of instability of the Sm locus has been studied. In contrast to the Treffers mutator gene, the new mutator character was not found to follow the pattern of a chromosomial factor in genetic cross. The character was found to possess the properties generally ascribed to genetic determinants of an episome nature: (i) a spontaneous loss of the character, enhanced by treatment with ultraviolet irradiation and acridine dyes; (ii) a loss which apparently is permanent; and (iii) a transfer to a mutator-negative cell by infection, both to a homologous mutator-negative mutant and to a K-12 strain. This infection is favored by the presence of the F factor in the donor.

TRANSDUCTION OF THE MU‐FACTOR IN ESCHERICHIA COLI

“…It is, howeve r, ex pressed befo re th e fir st cell di vis ion, su gges tin g it is n ot recessive ( 10 ). Th e p a rti cul a r streptomycin res is ta n ce of th e celt s ca rryin g th e mutato r fac tor in its ex tra chrom osom a l s tat e will protect th e cell s aga in s t quite high concentrations of s tre ptom ycin, at leas t 200 llg per ml when th ey are grow in g in minim a l m edium ( 4). Ther e is reason to beli eve th a t th e appa rent need for phenomic lag when selec ting for reco mbinants with 100 llg of s trep tom ycin per ml, as was done in th e expe rim ents lis ted in T abl e 1, is not a n actual phenomic lag a llowin g tim e for integ ration a nd seg rega tion of a gen e ti c mark e r, but rather a chan ge in the physiologi cal condition of the cell s. S U ~I r.J A R Y Tran sdu c tion t echniqu e h as b ee n appli ed as a n a ttempt to further elu cid a te th e ge n eti c n a ture of th e s trep tom yc in resistanc e resulting fro m th e ac tion of th e muta tor factor in E .…”

“…Thu s the fact was revealed that th e presence of the mutator fac tor in its extrachromosomal st a le protects the cell s against the lethal eff ect of s trep tom ycin und e r certa in conditions. Th e r esults from inves ti gation of this problem are reported elsewhere (4) . The present experim ents show that it is possible to transfer th e mutator factor from a mutator or a mutator-streptomycinresistant cell to a mutator-nega tive cell by m ea ns of tran sd ucing phage as well as by infection.…”

“…Growth experim ents in presen ce of s treptomyc in indica te that the presence of th e muta tor factor in the cell wi ll protec t the cell against low co ncentrations of s treptomycin rega rdl ess of the phys iological s tate of th e cell s a t th e tim e of ex pos ure (4) . It was of so m e interest to elucidate th e tim e when this low-level s treptomycin r esistance b eco m es gen eti cally ex pressed .…”

Fate of Exogenous Dna in Neisseria Meningitidis

“…Bacterial strains. The strain used for the preparation of E. coli ISN extract was E. coli K12 T71 (10). The mutants of N .…”

TRANSFORMATION OF AUXOTROPHS OF NEISSERIA MENINGITIDIS

“…It will be noted that the technique u sed in this expe rim ent is analogous with th a t used in genetic cross in th e E. co li K 12 sys tem (8) . In th e enterobacterium th e conjugation takes p lace within a period m easured in minutes, and th e tim e-fac tor may be s tudi ed by m ea n s of interrupted mating.…”