A new approach to isolating siderophore-producing actinobacteria

Abstract

Aims: This study was conducted to investigate the application of 2,2'-dipyridyl as a new approach to isolating siderophore-producing actinobacteria.

Methods and results: Isolation of actinobacteria from soil was conducted by a soil dilution plate technique using starch-casein agar. Iron starvation was fostered by the incorporation of the iron chelator 2,2'-dipyridyl in the isolation medium. Pretreatment of the samples at an elevated temperature (40°C) ensured that the majority of nonsporulating bacteria were excluded. The survivors of this treatment were largely actinobacteria. Of the viable cultures grown in the presence of 2,2'-dipyridyl, more than 78-88% (average of three separate studies) were reported to produce siderophore-like compounds compared to 13-18% (average of three separate studies) when grown on the basic media in the absence of the chelating agent. The most prolific producers as assessed by the chrome azurol sulphate (CAS) assay were further characterized and found to belong to the genus Streptomyces.

Conclusions: Selective pressure using 2,2'-dipyridyl as an iron-chelating agent in starch-casein media increased the isolation of siderophore-producing actinobacteria compared to the unamended medium.

Significance and impact of the study: The study described represents a new approach to the isolation of siderophore-producing actinobacteria using a novel procedure that places a selection on cell population based upon the incorporation of a chelating agent in the medium.