A mutant of
S. aureofaciens characterized by lower growth and higher tetracycline production than its parent strain is described. The mutant has a limited degree of temperature-sensitivity and shows a lower efficiency in the utilization of phosphate for growth and a higher cellular content of RNA. The data are in accordance with a possible mutation impairing some aminoacyl RNA synthetases. This kind of mutation might explain the lower growth in phosphate limited conditions and the higher content of RNA.