Effects of pH and Anoxia on the Cell Morphology and X-Ray Sensitivity of Escherichia coli

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Abstract
Escherichia coli, B/r, was cultured aerobically and anaerobically at pH 5 and 8.5, and irradiated in air or nitrogen with 50 Kv X-rays. Anaerobic cultures grown at pH 8.5 did not have the enhanced radio-resistance of pH 5 anaerobic cultures. Previous workers attributed this resistance of anaerobic cultures, which normally become acid. during growth, to increased anoxia within the cell during irradiation, while others suggested that it was due to multinuclearity. Phase contrast microscopy and DNA analysis support the latter hypothesis; anaerobic growth at pH 8.5 produced cells low in DNA and nuclear multiplicity. Such cells also show the same oxygen enhancement ratio as do anaerobic pH 5 cells or aerobically grown cells, further supporting the suggestion that anoxia during growth is not related to anoxia during irradiation.