Anotace:
The aim of this study was to screen and select streptomycetes exhibiting the production of extracellular proteases and evaluates the effect of carbon sources on protease expression. An acidic precipitation of non-degraded casein was performed to monitor the hydrolytic activity of protease-producing isolates on proteolysis medium (PM). Furthermore, we assessed the induction/repression status of protease production depending on the carbon sources. Clear halos surrounded the colonies were measured to calculate the Enzymatic Index (EI) values. One-hundred and sixty-eight streptomycete strains were screened in order to identify protease producers. Among all of these, the Streptomyces sp strain AGS-10 was selected based on their highest EI value. When sucrose, xylose, and arabinose were added to PM as carbon source, the EI were not modified. Conversely, the presence of lactose, glucose, and fructose repressed the proteolytic activity displayed by the AGS-10 colonies. A supernatant obtained from a culture media seeded with AGS-10 also displayed an extracellular proteolytic activity that was detected by an agar well diffusion assay. However, when lactose or glucose was added to the culture media the resulting proteolytic activity from supernatant was lost. The study shows a negative influence of some carbon sources for protease production.