Proteases constitute a significant part of cell wall-degrading enzymes (CWDEs)
produced by fungal biocontrol agents and particularly crucial in mycoparasitism
of fungal phytopathogens. Plate-based screening methods are routinely used for
screening protease-producing microorganisms including fungi. Skim milk agar
(SMA) is one of the most popular media for the detection of protease producing
bacteria. However, SMA is not efficient to test fast growing fungi, because it
does not give an estimation of the actual amount of secreted protease produced
by fungal inocula. In the current study, the efficacy of two modified
plate-screening methods, including split-SMA (SSMA) and minimal medium
supplemented with skim milk (MSMW) was assessed for detection of protease
production by three representative fungal strains including Trichoderma
longibrachiatum strain N, Beauveria bassiana
strain B and Purpureocillium lilacinum strain PL. Protease
production was revealed on the three tested media by the three strains. However,
the halo diameter of the fungal strains (a proxy for protease production) was
the smallest on SMA. Furthermore, protease production could not be detected for
T. longibrachiatum strain N on SMA due to its fast growth;
while it showed the highest protease activity on both modified media compared
with the other strains. According to the result of this study, the SSMA medium
is an easy and more accurate method compared with the two other different
methods as it displays the actual amount of protease produced by fungal strains
and therefore this method is recommended for quantitative and qualitative
detection of protease production by slow and fast growing fungi.
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