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Unexpectedly Diverse Mesorhizobium Strains and Rhizobium leguminosarum Nodulate Native Legume Genera of New Zealand, while Introduced Legume Weeds Are Nodulated by Bradyrhizobium Species. Bevan S. Weir, 2004.The New Zealand native legume flora are represented by four genera, Sophora, Carmichaelia, Clianthus, and Montigena . The adventive flora of New Zealand contains several legume species introduced in the 19th century and now established as serious invasive weeds . Until now, nothing has been reported on the identification of the associated rhizobia of native or introduced legumes in New Zealand . The success of the introduced species may be due, at least in part, to the nature of their rhizobial symbioses . This study set out to address this issue by identifying rhizobial strains isolated from species of the four native legume genera and from the introduced weeds: Acacia spp . (wattles), Cytisus scoparius (broom), and Ulex europaeus (gorse) . The identities of the isolates and their relationship to known rhizobia were established by comparative analysis of 16S ribosomal DNA, atpD, glnII, and recA gene sequences . Maximum-likelihood analysis of the resultant data partitioned the bacteria into three genera . Most isolates from native legumes aligned with the genus Mesorhizobium, either as members of named species or as putative novel species . The widespread distribution of strains from individual native legume genera across Mesorhizobium spp . contrasts with previous reports implying that bacterial species are specific to limited numbers of legume genera . In addition, four isolates were identified as Rhizobium leguminosarum . In contrast, all sequences from isolates from introduced weeds aligned with Bradyrhizobium species but formed clusters distinct from existing named species . These results show that native legume genera and these introduced legume genera do not have the same rhizobial populations . Suppressive Subtractive Hybridization Detects Extensive Genomic Diversity in Thermotoga maritima. Camilla L. Nesbø, 2002.Comparisons between genomes of closely related bacteria often show large variations in gene content, even between strains of the same species . Such studies have focused mainly on pathogens; here, we examined Thermotoga maritima, a free-living hyperthermophilic bacterium, by using suppressive subtractive hybridization . The genome sequence of T . maritima MSB8 is available, and DNA from this strain served as a reference to obtain strain-specific sequences from Thermotoga sp . strain RQ2, a very close relative (  96% identity for orthologous protein-coding genes, 99.7% identity in the small-subunit rRNA sequence) . Four hundred twenty-six RQ2 subtractive clones were sequenced . One hundred sixty-six had no DNA match in the MSB8 genome . These differential clones comprise, in sum, 48 kb of RQ2-specific DNA and match 72 genes in the GenBank database . From the number of identical clones, we estimated that RQ2 contains 350 to 400 genes not found in MSB8 . Assuming a similar genome size, this corresponds to 20% of the RQ2 genome . A large proportion of the RQ2-specific genes were predicted to be involved in sugar transport and polysaccharide degradation, suggesting that polysaccharides are more important as nutrients for this strain than for MSB8 . Several clones encode proteins involved in the production of surface polysaccharides . RQ2 encodes multiple subunits of a V-type ATPase, while MSB8 possesses only an F-type ATPase . Moreover, an RQ2-specific MutS homolog was found among the subtractive clones and appears to belong to a third novel archaeal type MutS lineage . Southern blot analyses showed that some of the RQ2 differential sequences are found in some other members of the order Thermotogales, but the distribution of these variable genes is patchy, suggesting frequent lateral gene transfer within the group .
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