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 gr owth and physiology and 20 by 16 S rRNA sequence analysis. Thirty-nine stra ins were fast-growing rhizobia, and 94 slow-growing bradyrhizobia. The latt er were essentially acid-tolerant, alkali-sensitive and salt-sensitive, whi le the former varied in acid-tolerance and were alkali- and salt-tolerant. In addition many of the rhizobia grew at 37 degrees C whereas few of the br adyrhizobia could. The fast-growing strains utilized disaccharides whereas the slow-growing bradyrhizobia did not. Using PCR a 260-264 bp segment of t he 16 S rRNA gene was amplified and then sequenced. The fast-growing rhizob ia can be divided into at least two groups-one showing similarity to Rhizob ium leguminosarum biovar phaseoli and the other to R. tropici. The slow-gro wers showed relationships to either Bradyrhizobium japonicum or Bradyrhizob ium spp. (Lupinus). (C) 1999 Elsevier Science Ltd. All rights reserved.