Abstract

Siderophores, a high-affinity chelating agents for ferric iron, is one of the mechanisms by which biocontrol agents’ act in inhibiting the growth of phytopathogens. Bacillus subtilisQM3, a siderophore producer, is a potential biocontrol agent. In this study, a simple double-layered chrome azurol S agar (SD-CASA) plate assay was developed. We further studied optimal conditions for detection siderophore production by B. subtilis QM3 using various history cultures, pH value, amino acid, and different carbon-nitrogen ratio as four variables. After incubating different history cultures we found out that the LB medium presented strong significant CAS reaction even for 12 h, and with the help of changingvariables on SD-CASA plate assisting paper-disc diffusion, strain QM3 from LB medium with Fe³⁺ (10 μmol/L) showed difference interestingly. In addition, CAS reaction and growth reaction also increased with pH 7.0, tryptophan 10 μmol/L and carbon-nitrogen ratio 5:1. The findings on solid medium were similar as that in liquid medium. The SD-CASA assay should be a useful tool for screening potential biocontrol microorganisms by siderophore production.

Key words: A simple double-layered CAS agar assay, paper-disc diffusion, siderophores,Bacillus subtilis QM3.