Factors influencing the production of extracellular proteinase by Pseudomonas fluorescens *

— Some of the factors influencing the production of extracellular proteinase by three strains of Pseudomonas fluorescens were studied. Tryptic Soy Broth supported good growth and enzyme production by all three strains. Poor enzyme yields resulted from growth in Nutrient Broth, Brain Heart Infusion and Peptone Yeast Extract. Addition of 0.2% (w/v) Skim Milk Powder to citrate mineral salts or Nutrient Broth stimulated enzyme production. Maximum yields of enzyme on mineral salts medium containing skim milk were obtained when pyruvate was the source of carbon; activity was low when glucose or citrate were used. Glutamine, when added as the sole carbon and/or nitrogen source, supported enzyme synthesis. At 5, 10, 15 and 20°C enzyme levels increased with increasing skim milk concentration. At 5°C enzyme activity was approximately 55% of that found at 20°C. A filter‐sterilized or autoclaved high‐speed centrifuged supernatant from skim milk strongly induced the proteinase. A small molecular weight (<5000) fraction obtained from a Sephadex G‐100 separation of skim milk supernatant actively stimulated enzyme production; fractions containing large molecular weight proteins were ineffective inducers. The maximum rate of enzyme production occurred during the late log and early stationary phases of growth at both 5 and 20°C.