Increased production of the important broad-range endolytic protease proteinase K by the fungus Parengyodontium album through adaptation of the growth medium.

Proteinase K is an extracellular protease produced by the fungus Parengyodontium album (formerly known as Tritirachium album). Proteinase K has a broad range of applications and is used in e.g. diagnostic kits to break down contaminating proteins. Supply shortages of proteinase K during the COVID-19 pandemic contributed to delays in testing, prompting us to improve the production process. The current proteinase K production process uses a specific P. album strain and a culture medium containing corn steep liquor, casein peptone and soybean protein. In this process, proteinase K is secreted by P. album together with another protease named “aminopeptidase”. In a standard production process the proteinase K yield is 0.260 ± 0.018 U/mL. In another series of experiments, soybean protein successfully replaced casein peptone, which was part of the previously employed standard production medium. This growth medium now enables the animal-free production of proteinase K (0.299 ± 0.012 U/mL) without reducing the proteinase K yield. Furthermore, we found that proteinase K levels were higher when other protein-containing components, such as feather meal, wheat bran or brown lentils, were present. In shake flasks containing 28 g/L wheat bran, 6 g/L feather meal, 5 g/L Soy Supro® and 3 g/L corn steep liquor, proteinase K activity increased up to 0.539 ± 0.033 U/mL over 96 h of cultivation. Finally, when 8.4 g/L glucose, 8.5 g/L soy protein and 9 g/L lentils were used as nitrogen source, proteinase K activity reached a yield of 0.485 ± 0.017 U/mL.