An improved selection technique and medium for the isolation and enumeration of Azospirillum brasilense

Abstract

An improved selection technique for isolation and enumeration of Azospirillum brasilense was developed. The technique is based on successive liquid enrichments in nitrogen-free semisolid medium supplemented with streptomycin, followed by the most probable number counting method and verification on a selective medium. The latter is based on Okon's nitrogen-free medium supplemented with cycloheximide (250 mg/L), streptomycin sulphate (200 mg/L), sodium deoxycholate (200 mg/L), 2,3,5-triphenyltetrazolium chloride (15 mg/L), and Congo red (1000 mg/L). This medium was found to be superior to other available diagnostic media. The technique was readily applied to detect and count A. brasilense Cd in inoculated wheat roots.