Enumeration of oligotrophic rhizosphere pseudomonads with diluted and selective media formulations.

Diluted and selective media formulations were evaluated for the recovery of oligotrophic pseudomonads from the rhizosphere of the cucumber plant ( Cucumis sativus L.). Full-strength King's B medium (KB) and 250-fold diluted medium (KB/250) were used as the basal formulations. The selective media formulations were: (1) Novobiocin, penicillin, and cycloheximide; (2) crystal violet and nitrofurantoin; and (3) Irgasan. On average, more rhizobacteria were recovered on the KB/250 than on the KB medium. For the recovery of pseudomonads, media made selective with either the novobiocin-penicillin-cycloheximide or the crystal violet and nitrofurantoin formulations were superior to the Irgasan formulation. Attempts to identify isolates using phospholipid fatty acid profiling met with limited success. The test isolates yielded mostly low similarity indices or 'no matches' with the Microbial Identification System (aerobic library version) used for this study. All oligotrophic isolates were facultative and no evidence was obtained for the presence of obligate oligotrophs in these plating experiments. [ABSTRACT FROM AUTHOR]