The genome of the versatile nitrogen fixer Azorhizobium caulinodans ORS571.
BACKGROUND
Biological nitrogen fixation is a prokaryotic process that plays an essential role in the global nitrogen cycle. Azorhizobium caulinodans ORS571 has the dual capacity to fix nitrogen both as free-living organism and in a symbiotic interaction with Sesbania rostrata. The host is a fast-growing, submergence-tolerant tropical legume on which A. caulinodans can efficiently induce nodule formation on the root system and on adventitious rootlets located on the stem.


RESULTS
The 5.37-Mb genome consists of a single circular chromosome with an overall average GC of 67% and numerous islands with varying GC contents. Most nodulation functions as well as a putative type-IV secretion system are found in a distinct symbiosis region. The genome contains a plethora of regulatory and transporter genes and many functions possibly involved in contacting a host. It potentially encodes 4717 proteins of which 96.3% have homologs and 3.7% are unique for A. caulinodans. Phylogenetic analyses show that the diazotroph Xanthobacter autotrophicus is the closest relative among the sequenced genomes, but the synteny between both genomes is very poor.


CONCLUSIONS
The genome analysis reveals that A. caulinodans is a diazotroph that acquired the capacity to nodulate most probably through horizontal gene transfer of a complex symbiosis island. The genome contains numerous genes that reflect a strong adaptive and metabolic potential. These combined features and the availability of the annotated genome make A. caulinodans an attractive organism to explore symbiotic biological nitrogen fixation beyond leguminous plants.
Laboratory of Plant Biotechnology, Biotechnology Research Center, University of Tokyo, Tokyo 113-8657, Japan. kyulee@genes.nig.ac.jp
Kyung-Bum
KB
Lee
Philippe
P
De Backer
Toshihiro
T
Aono
Chi-Te
CT
Liu
Shino
S
Suzuki
Tadahiro
T
Suzuki
Takakazu
T
Kaneko
Manabu
M
Yamada
Satoshi
S
Tabata
Doris M
DM
Kupfer
Fares Z
FZ
Najar
Graham B
GB
Wiley
Bruce
B
Roe
Tim T
TT
Binnewies
David W
DW
Ussery
Wim
W
D'Haeze
Jeroen Den
JD
Herder
Dirk
D
Gevers
Danny
D
Vereecke
Marcelle
M
Holsters
Hiroshi
H
Oyaizu
D020561:Alphaproteobacteria / Q000145:classification / Q000235:genetics; D020599:Azorhizobium caulinodans / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D001482:Base Composition; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology; D016680:Genome, Bacterial; D009586:Nitrogen Fixation / Q000235:genetics; D010802:Phylogeny; D018741:Replication Origin; D013559:Symbiosis / Q000235:genetics / Q000502:physiology; D020584:Xanthobacter / Q000145:classification / Q000235:genetics
D004269:DNA, Bacterial