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.
Lee
Kyung-Bum
KB
Laboratory of Plant Biotechnology, Biotechnology Research Center, University of Tokyo, Tokyo 113-8657, Japan. kyulee@genes.nig.ac.jp
De Backer
Philippe
P
Aono
Toshihiro
T
Liu
Chi-Te
CT
Suzuki
Shino
S
Suzuki
Tadahiro
T
Kaneko
Takakazu
T
Yamada
Manabu
M
Tabata
Satoshi
S
Kupfer
Doris M
DM
Najar
Fares Z
FZ
Wiley
Graham B
GB
Roe
Bruce
B
Binnewies
Tim T
TT
Ussery
David W
DW
D'Haeze
Wim
W
Herder
Jeroen Den
JD
Gevers
Dirk
D
Vereecke
Danny
D
Holsters
Marcelle
M
Oyaizu
Hiroshi
H
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