Azospirillum genomes reveal transition of bacteria from aquatic to terrestrial environments.

• Main Authors: Florence Wisniewski-Dyé, Kirill Borziak, Gurusahai Khalsa-Moyers, Gladys Alexandre, Leonid O Sukharnikov, Kristin Wuichet, Gregory B Hurst, W Hayes McDonald, Jon S Robertson, Valérie Barbe, Alexandra Calteau, Zoé Rouy, Sophie Mangenot, Claire Prigent-Combaret, Philippe Normand, Mickaël Boyer, Patricia Siguier, Yves Dessaux, Claudine Elmerich, Guy Condemine, Ganisan Krishnen, Ivan Kennedy, Andrew H Paterson, Victor González, Patrick Mavingui, Igor B Zhulin
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2011-12-01
• Series: PLoS Genetics
• Online Access: http://europepmc.org/articles/PMC3245306?pdf=render

Fossil records indicate that life appeared in marine environments ∼3.5 billion years ago (Gyr) and transitioned to terrestrial ecosystems nearly 2.5 Gyr. Sequence analysis suggests that "hydrobacteria" and "terrabacteria" might have diverged as early as 3 Gyr. Bacteria of the genus Azospirillum are associated with roots of terrestrial plants; however, virtually all their close relatives are aquatic. We obtained genome sequences of two Azospirillum species and analyzed their gene origins. While most Azospirillum house-keeping genes have orthologs in its close aquatic relatives, this lineage has obtained nearly half of its genome from terrestrial organisms. The majority of genes encoding functions critical for association with plants are among horizontally transferred genes. Our results show that transition of some aquatic bacteria to terrestrial habitats occurred much later than the suggested initial divergence of hydro- and terrabacterial clades. The birth of the genus Azospirillum approximately coincided with the emergence of vascular plants on land.