Airborne transmission of the rhizosphere bacteriumAzospirillum.

In controlled environments, plants inoculated withAzospirillum brasilense caused the contamination of noninoculated plants via air transmission. This was detected up to 6 m from the inoculation source. In the temperate agricultural zone studied in field experiments, localAzospirillum strains were detected year-round. Other diazotrophs showed a similar distribution pattern. It is proposed that (1) contamination fromAzospirillum-inoculated plants may occur via airborne bacteria, (2) local azospirilla and other diazotrophs have an airborne phase in temperate agricultural zones, and (3) because of the existence of an airborne phase for Gram-negative rhizosphere bacteria, inoculation presents a risk of uncontrolled airborne contamination.