Azospirillum genomes reveal transition of bacteria from aquatic to terrestrial environments.
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.
CNRS, UMR 5557, Ecologie Microbienne, Université de Lyon, Villeurbanne, France.
Florence
F
Wisniewski-Dyé
Kirill
K
Borziak
Gurusahai
G
Khalsa-Moyers
Gladys
G
Alexandre
Leonid O
LO
Sukharnikov
Kristin
K
Wuichet
Gregory B
GB
Hurst
W Hayes
WH
McDonald
Jon S
JS
Robertson
Valérie
V
Barbe
Alexandra
A
Calteau
Zoé
Z
Rouy
Sophie
S
Mangenot
Claire
C
Prigent-Combaret
Philippe
P
Normand
Mickaël
M
Boyer
Patricia
P
Siguier
Yves
Y
Dessaux
Claudine
C
Elmerich
Guy
G
Condemine
Ganisan
G
Krishnen
Ivan
I
Kennedy
Andrew H
AH
Paterson
Victor
V
González
Patrick
P
Mavingui
Igor B
IB
Zhulin
D059001:Aquatic Organisms / Q000235:genetics*; D016949:Azospirillum / Q000235:genetics*; D001483:Base Sequence; D005075:Biological Evolution; D017753:Ecosystem; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D020043:Genes, Essential / Q000235:genetics; D016680:Genome, Bacterial / Q000235:genetics*; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012244:Rhodospirillaceae / Q000235:genetics*
D012336:RNA, Ribosomal, 16S; D006026:Glycoside Hydrolases