Identification and characterization of fast- and slow-growing root nodule bacteria from South-Western Australian soils able to nodulate Acacia saligna

A total of 133 root nodule bacterial strains were isolated from nodules of Acacia saligna growing in soils from nine geographically separate locations in South-Western Australia; 40 were characterized on the basis of their growth and physiology and 20 by 16 S rRNA sequence analysis. Thirty-nine strains were fast-growing rhizobia, and 94 slow-growing bradyrhizobia. The latter were essentially acid-tolerant, alkali-sensitive and salt-sensitive, while the former varied in acid-tolerance and were alkali- and salt-tolerant. In addition many of the rhizobia grew at 37°C whereas few of the bradyrhizobia could. The fast-growing strains utilized disaccharides whereas the slow-growing bradyrhizobia did not. Using PCR a 260–264 bp segment of the 16 S rRNA gene was amplified and then sequenced. The fast-growing rhizobia can be divided into at least two groups—one showing similarity to Rhizobium leguminosarum biovar phaseoli and the other to R. tropici. The slow-growers showed relationships to either Bradyrhizobium japonicum or Bradyrhizobium spp. (Lupinus).