Inhibition of ribonucleic acid degradation in bacteria by spermine.

A release of acid soluble constituents that absorb at 260 mp occurs during the incubation of suspensions of Escherichia coli H (1)) Pseudomonas aeruginosa (2)) or Lactobacillus arabinosus (3) in buffers. Lysogenic E. coli strain Klz as well as nonlysogenie E. coli strains B and B/r excrete ultraviolet-absorbing substances during growth in media deficient in glucose, and a methionine-requiring auxotroph of lysogenic E. coli (strain K12W-6) excretes 260 mp-absorbing materials when incubated in methionine-free growth medium (4). During methionine starvation the cells remained fully viable but there was no increase in the number of viable cells. Holme and Palmstierna (5) incubated E. coli B in nitrogen-deficient media and observed the accumulation in the culture medium of substances causing an absorption in the ultraviolet region. Cells of Rickettsia mooseri lost 260 mp-absorbing materials in isotonic media incubated at 36” and there was a complementary decrease in the nucleic acid fraction of rickettsial suspensions (6). We have reported (7) the release of acid soluble constituents that absorb at 260 mp during the incubation of washed cells of Hemophilus parainsuenzae in water or buffers. The 260 rnpabsorbing “leakage” was derived from the ribonucleic acid fraction of the cell suspension and the temperature and pH characteristics of the reaction suggested that it is an enzymatic process. In the presence of the polyamine, spermine, which is an essential growth factor for H. parainfluenzae (8), the leakage and the associated nucleic acid breakdown is reduced or eliminated. The inhibition of nucleic acid degradation in the cell suspensions was deemed a consequence of nucleic acid-spermine complex formation (9, 10). The experiments described in this paper more fully characterize the leakage of 260 rnp-absorbing materials from suspensions of H. parainjluenzae in buffers or growth media as an autolytic degradation of cellular ribonucleic acid by a very active ribonuclease. The enzymatic degradation of bacterial ribonucleic acid can be reduced or completely inhibited by the addition of spermine to the bacterial suspensions.