DNA replication and transcription in synchronous cultures of Escherichia coli and Proteus mirabilis



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A new method is described for the cell division synchronization of Escherichia coli and Proteus mirabilis under balanced growth conditions in large volumes with high per cent phasing. By use of the stationary-phase method of synchrony, selected DNA segments were isolated from Hfr E. coli in cellular division and genomic synchrony. The uniqueness of these fractions was confirmed by cross-testing for similar base sequences, using the DNA-DNA complementation technique. Further studies using the isolated DNA segments of the genome showed a characteristic transcription activity pattern of the genome throughout the cell division cycle. Transcription of messenger RNA does not appear to be related to the position of the DNA replication point, whereas transcription of ribosomal RNA does indicate such a relationship. Two separate locations on the genome were found to be complementary for 16S, 23S and transfer RNA. The direction and point of initiation of the DNA replication cycle was determined by cross-testing the different segments of the genome for sequence homology with RNA transcribed by [lambda] and 424 bacteriophages. DNA replication was found to initiate near the Origin and to proceed towards the F factor, replicating [lambda] before 424. Pair formation and chromosome transfer were studied as a function of the cell division cycle in Hfr and F^- E. coli cultures undergoing conjugation. Fertility and mating pair formation for Hfr cells were found to be a function of the cell division cycle but were independent of the cell division cycle for F^- cells. Visible light (420 mµ) was found to inhibit the cell division cycle of synchronous cultures of Proteus mirabilis. The cells were the least sensitive to the irradiation approximately half way through the cell division cycle. A theoretical model is presented to explain the different generation times and their distribution that are characteristic for various bacterial strains. The model is based on a redundancy in informational content of the bacterial cell and of its random destruction. The model predicts a redundancy of informational content of about five-fold for Proteus vulgaris and a destruction rate of this information at about 4.5 x 10^-2 bits per generation per bacterium.