Research Article The Plant Growth-Promoting Bacteria Azospirillum amazonense: Genomic Versatility and Phytohormone Pathway

Copyright © 2015 Ricardo Cecagno et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The rhizosphere bacterium Azospirillum amazonense associates with plant roots to promote plant growth. Variation in replicon numbers and rearrangements is common amongAzospirillum strains, and characterization of these naturally occurring differences can improve our understanding of genome evolution. We performed an in silico comparative genomic analysis to understand the genomic plasticity ofA. amazonense.The number ofA. amazonense-specific coding sequences was similar when compared with the six closely related bacteria regarding belonging or not to theAzospirillum genus.Our results suggest that the versatile gene repertoire found in A. amazonense genome could have been acquired from distantly related bacteria from horizontal transfer. Furthermore, the identification of coding sequence related to phytohormone production, such as flavin-monooxygenase and aldehyde oxidase, is likely to represent the tryptophan-dependent TAM pathway for auxin production in this bacterium. Moreover, the presence of the coding sequence for nitrilase indicates the presence of the alternative route that uses IAN as an intermediate for auxin synthesis, but it remains to be established whether the IAN pathway is the Trp-independent route. Future investigations are necessary to support the hypothesis that its genomic structure has evolved to meet the requirement for adaptation to the rhizosphere and interaction with host plants. 1