Evaluation of extracellular protease activities of soil bacteria

Abstract Nutrient agar, albumin agar and azocoll agar media were used to screen soil proteolytic bacteria from paddy fields. Proteolytic activity was compared by evaluating extracellular hydrolytic activities toward benzyloxycarbonyl- l -phenylalanyl- l -leucine (z-FLase), benzyloxycarbonyl- l -phenylalanyl- l -tyrosyl- l -leucine (z-FTLase) and casein (caseinase). The average z-FLase activity (10.6 nKat g −1 protein) of bacteria capable of gelatin liquefaction isolated from azocoll nutrient agar (ANB/GL, 37 isolates) was 33.7 times that of bacteria capable of gelatin liquefaction isolated from nutrient agar (NB/GL, 24 isolates) and 6.7 times that of actinomycetes capable of gelatin liquefaction isolated from albumin agar (AA/GL, 33 isolates), the z-FTLase activity (24.5 nKat g −1 protein) was 41.3 times that of NB/GL and 6.2 times that of AA/GL, and caseinase activity (34.0 nKat g −1 protein) was 27.8 times that of NB/GL and 14.0 times that of AA/GL. Therefore, azocoll nutrient agar was an effective isolation medium for screening soil bacteria with extremely high extracellular protease activities.