NON-LETHAL ASSIMILATION AND DISTRIBUTION OF RADIOACTIVE PHOSPHORUS IN SERRATIA MARCESCENS

Abstract

Optimal conditions for non-lethal assimilation of radioactive phosphorus by Serratia marcescens have been studied. Ten microcuries or less of P32per 300 ml of medium has no significant lethal effect on the test organism. The presence of 1% w/v glucose in the culture medium stimulates phosphorus assimilation causing an increase of approximately 34%. Phosphorus assimilation over a 24 hour period increases by approximately 50% when cultures are incubated at 30 °C rather than 37 °C.The concentration of P32in the various cellular constituents has been determined at various intervals during 24 hour incubation. Incorporation of P32in the acid-soluble and lipid fractions of the cell begins almost immediately whereas there is a slight delay prior to incorporation into the R.N.A. and longer delay before incorporation into D.N.A. Sixty to 65% of the P32assimilated by the bacterial cell is incorporated into the nucleic acids. Although R.N.A. has the highest specific activity of the cell fractions studied, the phospholipid fraction also has high specific activity.