What does the published scientific research say about Azospirillum amazonense?

Azospirillum amazonense — reclassified and now formally named Nitrospirillum amazonense — is a rhizosphere and endophytic diazotroph with 8 PubMed articles documenting its role as a plant growth-promoting bacterium. Genomic analyses identify gene clusters for biological nitrogen fixation (BNF) and auxin biosynthesis, including the tryptophan-dependent TAM pathway via flavin-monooxygenase and aldehyde oxidase, plus a nitrilase gene suggesting an alternative IAN-intermediate route for indole-3-acetic acid (IAA) production.

The peer-reviewed literature on Nitrospirillum amazonense is concentrated in sugarcane systems. Inoculant studies report the strain's colonization of roots and shoots, its detection by species-specific qPCR primers, and its ranking second in substrate survival among five commercial diazotrophic strains. One field trial cited in the literature reported a 12.2% stalk-yield increase and a 13.7% sugar-yield gain when N. amazonense was combined with Azospirillum brasilense, though researchers note differences between single-strain and mixed treatments were not pronounced.

A 2025 herbicide-compatibility study found molecule-specific effects: indaziflam, metribuzin, S-metolachlor, and sulfentrazone did not harm bacterial survival or BNF activity, while flumioxazin and tebuthiuron reduced IAA production. Researchers highlight herbicide selection as a key factor in preserving microbial benefits in integrated sugarcane management — a practical consideration for growers asking whether Azospirillum amazonense inoculants are compatible with standard pre-emergent programs.