Azorhizobium caulinodans ORS571 is a rhizobium of the tropical legume Sesbania rostrata, which induces nitrogen-fixing nodules on the roots and stems of the host plant. Inside the nodules, A. caulinodans ORS571 invades host cells and fixes atmospheric nitrogen. Generally, rhizobia fix nitrogen only in the symbiotic state, but A. caulinodans ORS571 has a unique ability to fix nitrogen even at free-living states. Furthermore, A. caulinodans ORS571 is an endophytic bacterium with the capacity to colonize root tissues of non-leguminous plants and fix atmospheric nitrogen.
Our challenge is to understand the mechanism underlying the leguminous and non-leguminous symbioses of this rhizobium. We sequenced the whole genome of A. caulinodans ORS571, and performed genome-wide mutagenesis and transcriptional profiling experiments. These results identified new genetic factors involved in nodule development. Currently, we are working to determine the functions and roles of these genes in leguminous and non-leguminous symbioses. We are particularly focusing on pathogenic features such as R-body production, which should be stringently repressed to establish symbiotic relationships with plants.

Publications (selected)

• Nakajima A, Aono T, Tsukada S, Siarot L, Ogawa T, Oyaizu H (2012) Lon protease of Azorhizobium caulinodans ORS571 is required for the suppression of reb gene expression. Appl. Environ. Microbiol. 78: 6251-6261.
• Akiba N, Aono T, Toyazaki H, Sato S, Oyaizu H (2010) phrR-like gene praR of Azorhizobium caulinodans ORS571 is essential for symbiosis with Sesbania rostrata and is involved in expression of reb genes. Appl. Environ. Microbiol. 76: 3475-3485.
• Tsukada S, Aono T, Akiba N, Lee KB, Liu CT, Toyazaki H, Oyaizu H (2009) Comparative genome-wide transcriptional profiling of Azorhizobium caulinodans ORS571 grown under free-living and symbiotic conditions. Appl. Environ. Microbiol. 75: 5037-5046.
• Lee KB, De Backer P, Aono T, Liu CT, Suzuki S, Suzuki T, Kaneko T, Yamada M, Tabata S, Kupfer DM, Najar FZ, Wiley GB, Roe B, Binnewies TT, Ussery DW, D'Haeze W, Herder JD, Gevers D, Vereecke D, Holsters M, Oyaizu H (2008) The genome of the versatile nitrogen fixer Azorhizobium caulinodans ORS571. BMC Genomics 9: 271.
• Suzuki S, Aono T, Lee KB, Suzuki T, Liu CT, Miwa H, Wakao S, Iki T, Oyaizu H (2007) Rhizobial factors required for stem nodule maturation and maintenance in Sesbania rostrata-Azorhizobium caulinodans ORS571 symbiosis. Appl. Environ. Microbiol. 73: 6650-6659.