Use of CAS-agar plate modified to study the effect of different variables on the siderophore production by Aspergillus

Aims: To evaluate the suitability of chrome azurol S (CAS) agar plate assay as a quantitative methodology for siderophore production. Methods and Results: Aspergillus species (A. flavus, A. niger, A. tamarii) were inoculated in the CAS-agar plates and the siderophores production was determined and expressed as CAS-reaction rate (mm per day). All the species showed positive CAS reaction with different rates depending on culture conditions and A. flavus showed the highest CAS-reaction rate. The siderophore production in solid medium expressed as CAS-reaction rate was correlated with siderophore production in liquid medium. Conclusions: The use of CAS-agar plate assay was modified and the evaluation of CAS reaction in mm per day made it possible to study and quantify the effect of several variables on the siderophore production by Aspergillus fungi. Significance and Impact of the Study: We describe the CAS-agar plate assay as a quantitative methodology, which make it possible to select and evaluate the siderophore production by several microorganisms (fungi and bacteria) according to different culture conditions.