The effects of ribonucleic acid and deoxyribonucleic acid on the growth of Myeoplasma.

Abstract

SUMMARY: The nucleic acid requirements of several Mycoplasma organisms were examined in a partially denned medium. The saprophytic M. laidlawii strain A did not grow in the basal medium alone Razin & Knight, 1960 a but did when suitable concentrations of ribonucleic acid (RNA) and of deoxyribonucleic acid (DNA) were added. Too high a concentration of RNA inhibited growth; this inhibition was annulled by increasing the concentration of DNA. Similarly, too high a concentration of DNA inhibited growth, and this inhibition was annulled by RNA. Chemical and enzymic degradations of RNA showed that the growth-promoting effect could be brought about by a ribo-oligonucleotide but not by smaller fragments of the molecule. Similar degradations of DNA showed that the effective moiety was thymidine; thymine was less effective. The degradation of RNA abolished its growth-inhibitory activity. The growth-inhibitory activity of DNA was not affected by its degradation to oligonucleotides, and was only partially diminished by its degradation to nucleotides or nucleosides. Mycoplasma laidlawii strain B grew in the basal medium when DNA alone was added. This nutritional requirement was also satisfied by thymidine, provided that some RNA was also present. The parasitic Mycoplasma mycoides var. capri resembled M. laidlawii strain B in responding to DNA alone, but differed from the saprophytic strains in its complete indifference to high DNA concentrations. Thymidine replaced DNA only to a certain extent when added together with RNA. A growth-promoting effect of DNA was also found with the L-phase of Streptobacillus moniliformis; thymidine then replaced DNA completely. The RNA/DNA antagonism was found with all the organisms examined. Possible explanations for this phenomenon are discussed.