Enzyme-Linked Immunosorbent Assay for Specific Identification and Enumeration of Azospirillum brasilense Cd. in Cereal Roots

Abstract

The enzyme-linked immunosorbent assay is suggested as a reliable, sensitive, and highly specific method for the identification and enumeration of Azospirillum brasilense Cd. As few as 10 5 CFU/ml can be practically identified by this method. At higher bacterial numbers, sensitivity increased linearly up to 5 × 10 8 CFU/ml, yielding useful standard curves. No cross-reaction was found either with different closely related Azospirillum strains or with other rhizosphere bacteria. The method allows for a specific identification of A. brasilense Cd. both in pure cultures and in mixtures with other bacterial species, even when the colony morphology is variable. The method was successfully applied to assess the degree of root colonization on various cereals by A. brasilense Cd.