The effect of ribonucleic acid and deoxyribonucleic acid on the growth of mycoplasma

SUMMARY: The nucleic acid requirements of several Mycoplasma organisms were examined in a partially defined medium. The saprophytic M. laidmii strain A did not grow in the basal medium alone (Razin & Knight, 1960a) 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 concentra-tion 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 nucleo-tides or nucleosides. M y c o p l m laidlazvii strain B grew in the basal medium when DNA alone wa