Azospirillum brasilense

Azospirillum brasilense is a well studied, nitrogen-fixing (diazotroph), genetically tractable, Gram-negative, alpha-proteobacterium bacterium. A. brasilense is able to fix nitrogen in the presence of low oxygen levels, making it a microaerobic diazotroph. Originally isolated from nitrogen poor soils in the Netherlands in 1925, it is widely found in the rhizospheres of grasses around the world where it confers plant growth promotion. Whether growth promotion occurs through direct nitrogen flux from the bacteria to the plant or through hormone regulation is debated. The two most commonly studied strains are Sp7 (ATCC 29145) and Sp245. The genome of A. brasilense Sp245 has been sequenced and is 7Mbp in size and spread across 7 chromosomes. The high GC content (70%) makes it challenging to engineer. Sp245 can be transformed with OriV origin of replication plasmids through conjugation and electroporation. The strain is natively resistant to both spectinomycin and ampicillin antibiotics. Kanamycin resistance is used as a selectable marker. A. brasilense has a high evolutionary adaptation rate driven by codon mutation and transposon hopping. A strain originally classified as Roseomonas fauriae was reclassified as A. brasilense. It was first isolated from a hand wound of a woman in Hawaii in 1971, and was named for Yvonne Faur 'for her contributions to public health bacteriology and, specifically, for her contribution to the recognition of pink-pigmented bacteria.'