Abstract
A potential screening programme for fibrinolytic filamentous fungi in the Egyptian environment was done for the first time. The proteolytic activity was positive in 38.5% of isolates, whilst only thirty-four of them were able to produce fibrinolytic enzymes. The two most potent isolates were identified as
Aspergillus brasiliensis
AUMC 9735 and
Aspergillus flavus
AUMC 9736. Under submerged culture conditions, the two strains were able to excrete fibrinolytic enzymes, reaching a maximum at 5 and 9 days, respectively. Maximal enzyme productivity by both strains was achieved by lactose and sucrose, respectively. All tested nitrogen sources were stimulatory for enzyme production by both strains, except for ammonium acetate in the case of
A. brasiliensis
AUMC 9735. Purification of
A. brasiliensis
AUMC 9735 enzyme increased its specific activity to 83.5-fold with a recovery of 9.1% and molecular weight of 40 kDa. Maximal activity was recorded at pH 8 (stability at pH 6-11). The purified enzyme showed higher thermostability than most fibrinolytic enzymes of filamentous fungi with the midpoint temperature (
T
m
) value at 60.4°C and the half-life times (
t
1/2
) at 50-80°C being 672.1-6.5 min. Interestingly, the enzyme exhibited a good storage and solvent stability at 4°C for 60 days. Enzyme activity was totally lost in the presence of ethylenediaminetetraacetic acid and was restored after addition of Mg
2+
cations suggesting that the enzyme is a metalloprotease and Mg
2+
acts as a cofactor. This work reveals the potential of
A. brasiliensis
and many other fungal strains as an unconventional and unexplored production alternative to already known thrombolytic agents. The value of Egyptian environment as a reservoir of filamentous fungal species with promising biotechnological value could also be highlighted.