Abstract
A well-known and widely used method for detection of siderophore production by microorganisms in solid medium is the
universal chrome azurol S (CAS)-agar plate assay. However, the high toxicity of CAS-blue agar medium caused by the
presence of a detergent impedes its utilization with many varieties of fungi and Gram-positive bacteria. To solve this
problem, a modification of the CAS-agar plate assay was made by incorporating the CAS-blue dye in a medium with no
contact with the microorganisms tested. Half of each plate used in our experiments was filled with the most appropriate
culture medium for each type of microorganism and the other half with CAS-blue agar. This modification allowed us to
study several strains of fungi (basidiomycetes, deuteromycetes, ascomycetes and zygomycetes) and bacteria (Gram positive
and negative), some of them appearing for the first time in the literature. All the microorganisms grew properly and reacted
in different manners to the CAS assay. Some strains of wood-decaying basidiomycetes (mainly white-rot fungi) and
Aspergillus species produced the fastest color-change reactions in the CAS-blue agar. This modified method could facilitate
optimization of culture conditions, since both CAS-blue agar and growth medium were prepared and added in the Petri plate
separately. Ó 1999 Elsevier Science B.V. All rights reserved.
Keywords: Bacteria; Chrome azurol S; Fungi; Siderophore
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