Azospirillum brasilense

Azospirillum brasilense is a nitrogen-fixing, Gram-negative, alpha-proteobacterium first described in Brazil in 1978 by Johanna Döbereiner's group. It thrives in low-oxygen conditions as a microaerobic diazotroph and is commonly found in the rhizospheres of grasses worldwide, promoting plant growth. The mechanisms behind this promotion—whether through direct nitrogen transfer or hormone regulation—are debated. Two widely studied strains, Sp7 (ATCC 29145) and Sp245, were isolated from tropical grasses in Seropedica, Brazil.

The genome of A. brasilense Sp245 is 7 Mbp, spread across seven chromosomes with a high GC content of 70%, making genetic engineering challenging. The strain can be transformed using OriV origin plasmids via conjugation or electroporation and is naturally resistant to spectinomycin and ampicillin. Kanamycin resistance serves as a selectable marker. A. brasilense exhibits high evolutionary adaptability due to codon mutations and transposon activity.

A strain initially classified as Roseomonas fauriae was reclassified as A. brasilense. This isolate, named after Yvonne Faur for her contributions to public health bacteriology, was first identified in 1971 from a hand wound in Hawaii and is noted for its role in recognizing pink-pigmented bacteria.