Characterization and cyst production of azospirilla isolated from selected grasses growing in New Jersey and New York

Abstract

Species of Azospirillum were readily isolated from the roots of several grasses growing under a wide range of conditions in the New Jersey – New York area. The number of successful isolations from corn, rice, zoysia, and reed roots was relatively high (up to 87%). Based upon morphological and physiological characterization, six of the isolates appeared to be Azopirillum brasilense sp. nov., while two isolates more closely resembled Azospirillum lipoferum (Beijerinck) comb. nov. When grown in semisolid malate medium, the cells averaged 1.5 μm in diameter and ranged from 3 to 30 μm in length. Formation of larger S-shaped vegetative cells was evident only in A. lipoferum, but most important was the pleomorphism which was displayed by all isolates, as well as the reference cultures for A. lipoferum and A. brasilense. Upon prolonged incubation in semisolid and solid media, all isolates, as well as the reference cultures, produced thick-walled, cystlike ovoid structures which were quite distinct from the typical vibrioid or S-shaped cell morphology of this genus. Cysts were approximately 2.5 μm in diameter and from 3 to 15 μm in length. Cyst-enriched cultures were much more resistant to desiccation than normal vegetative cultures. Production of cysts may thus represent a mechanism by which azospirilla can persist in the rhizosphere during unfavorable environmental conditions.