Letter | Published:

Polyploidy in Bacteria?

Nature volume 162, page 295 (21 August 1948) | Download Citation



IN the course of experiments on the bactericidal action of X-rays on the R and S phases of Escherichia coli, it was found that the survival-rate in three stocks (76, 111, Ida), irradiated twenty-four hours after seeding, was different1; one of them (stock Ida) was more resistant to the radiation as compared with the other two stocks. No significant differences were found between S and R phases of the same strains. According to the hit-theory of biological effects of radiation the survival-rate is a measure of the target volume, which has been assumed to represent the bacterial ‘nucleus'2,3. If in the case of bacteria the so-called nucleoplasmic ratio of plants and animals holds true, and if, on the other side, the target volume obtained from X-ray experiments really represents the size of the bacterial ‘nucleus', one would expect the size of the bacterial cells to be correlated to the target volumes. A biometric analysis of twenty-four hours old bacteria, carried on the projected images of photomicrographs of bacteria stained with Henrici‘s Congo Red method4, has shown that E. coli with a larger target volume are larger than the ones with smaller target volume. The variability curves obtained for the three stocks were almost normal, and the differences found between their means were statistically significant. It is suggested that such correlation might indicate the presence of polyploidy among different stocks of the same bacterial species, as it has previously been found in other organisms. A detailed description of such experiments will be published elsewhere.

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  1. 1.

    , , and , Rivista di radiologia, 1, 43 (1947).

  2. 2.

    , "Die Physik und das Geheimnis des organischen Lebens" (Braunschweig, 1941).

  3. 3.

    , "Actions of Radiations on Living Cells" (Cambridge, 1946).

  4. 4.

    , "Morphologic Variation and the Rate of Growth of Bacteria" (London, 1928).

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  1. Department of Biophysics of the National Research Council, Pallanza (Novara), Italy.

  2. Istituto Sieroterapico Milanese, Serafino Belfanti, Milano, Italy. May 18.

    • L. L. CAVALLI


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