The current classification of the rhizobia (root-nodule symbionts) assigns them to six genera. It is strongly influenced by the small subunit (16S, SSU) rRNA molecular phylogeny, but such single-gene phylogenies may not reflect the evolution of the genome as a whole. To test this, parts of the atpD and recA genes have been sequenced for 25 type strains within the α-Proteobacteria, representing species in Rhizobium, Sinorhizobium, Mesorhizobium, Bradyrhizobium, Azorhizobium, Agrobacterium, Phyllobacterium, Mycoplana and Brevundimonas. The current genera Sinorhizobium and Mesorhizobium are well supported by these genes, each forming a distinct phylogenetic clade with unequivocal bootstrap support. There is good support for a Rhizobium clade that includes Agrobacterium tumefaciens, and the very close relationship between Agrobacterium rhizogenes and Rhizobium tropici is confirmed. There is evidence for recombination within the genera Mesorhizobium and Sinorhizobium, but the congruence of the phylogenies at higher levels indicates that the genera are genetically isolated. rRNA provides a reliable distinction between genera, but genetic relationships within a genus may be disturbed by recombination. Rhizobium, Sinorhizobium, Mesorhizobium, recA, atpD Keywords : INTRODUCTIONThe rhizobia are root-nodulating bacteria responsible for a significant part of the global fixation of nitrogen. The ability of rhizobia to nodulate plants and reduce N # is conferred by genes that are plasmid-borne in many species (Pueppke, 1996), and the lateral transfer The atpD and recA sequences and details of the SimPlot analyses are available as supplementary material in IJSEM Online (http :// ijs.sgmjournals.org/ ).Abbreviations : HKY85, Hasegawa-Kishino-Yano model ; K2P, Kimura's two-parameter model ; SSU, small subunit rRNA.The EMBL accession numbers for the sequences reported in this study are AJ294386-AJ294409 (atpD) and AJ294363-AJ294385 (recA). of these genes is the most likely explanation for their occurrence within several distinct clades of subgroup 2 of the α-Proteobacteria (Dobert et al., 1994 ; Kaijalainen & Lindstro$ m, 1989 ;Lindstro$ m et al., 1995 ;Young, 1998 ;Young & Johnston, 1989). The phylogeny of the nodulation genes is quite different from that of the small subunit rRNA (SSU or 16S rRNA) genes in these bacteria. As in other bacterial groups, the SSU phylogeny has had a major influence on our current perception of evolutionary relationships among rhizobia ( Willems & Collins, 1993 ;Young, 1996 ;Young et al., 1991). More than 20 species have been described, and they are classified into the genera Rhizobium, Sinorhizobium, Allorhizobium, Mesorhizobium, Bradyrhizobium and Azorhizobium as well as ' Methylobacterium nodulans ' (de Lajudie et al., 1994' (de Lajudie et al., , 1998b Dreyfus et al., 1988 ; Jarvis et al., 1997 ; Jordan, 1982 ;Sy et al., 2001 M. W. Gaunt and others ing much slower growth on laboratory media (Dreyfus et al., 1988 ; Fred et al., 1932 ; Jordan, 1982). They are also fairly distant in the SSU p...

SUMM.4RYThe internal transcribed spacer (ITS) region of the nuclear ribosomal RNA was amplified, cloned and sequenced from spores of five isolates of the arbuscular mycorrhizal fungus Glomus mosseae and one isolate each of G. fasciculatum, G. dimorphicum and G. coronatiim. The sequences comprised ITSl (113-121 base pairs), 5.SS rRNA gene (154 base pairs) and ITS2 (222-230 base pairs). The ITS sequences were at least 84% identical, but only distantly related to other published sequences. Their identification as Glomus sequences was confirmed by sequencing part of the adjoining SSU rRNA gene from one isolate; it was 98 °o identical to the published G. mosseae sequence. Two to four clones were sequenced from each isolate, and in many instances these were substantially different (up to 6 % divergence) even when they were obtained from a single spore. Sequences from a single isolate were generally, but not always, more similar to each other than to those from different isolates. In addition to base substitutions, many ITS sequences differed slightly in length because of the insertion or deletion of up to three nucleotides within short runs of a single base, generally A or T. These changes were found at 22 separate sites within the ITS, and were more common between than within isolates. Phylogenetic relationships deduced from length variation and from base substitution were similar. The variation among isolates from different continents (Europe, Asia, South America) was no greater than among those from a smaller geographic range. The ITSl and 2 sequences from G. coronatum were clearly distinct from the other isolates (11-16% divergence), but those of G. fasciculatum and G. dimorphicum fell w-ithin the range of variation exhibited by G. mosseae.

Abstract-Adrenocorticosteroid activity in Lyon hypertensive (LH) and low blood pressure (LL) rat strains differ in several respects. Abnormal activity of 11␤-hydroxysteroid dehydrogenase enzymes (11␤-HSD1 and 11␤-HSD2), which interconvert corticosterone and inactive 11-dehydrocorticosterone, might contribute to the LH phenotype by regulating corticosteroid hormone access to receptors. 11␤-HSD2 (expressed in kidney but not liver) prevents endogenous glucocorticoids from binding to mineralocorticoid receptors. 11␤-HSD1 (expressed in liver and kidney) favors active glucocorticoid formation from 11-dehydrocorticosterone. 11␤-HSD properties in LH and LL have been compared by several approaches: (1) 11␤HSD activities have been measured in vitro as corticosterone dehydrogenation and in vivo as interconversion of injected cortisol and cortisone; (2) the effects of cortisol and cortisone on urine electrolytes and volume have been measured; and (3) 11␤-HSD mRNA expression has been measured by in situ hybridization. 11␤-HSD2 enzyme activities in LH and LL rats were similar and urinary cortisone:cortisol ratios were not different after cortisol injection. Cortisol caused a natriuresis and kaliuresis in both strains, with a slightly reduced response in LH rats. Renal 11␤-HSD2 mRNA expression was slightly lower in LH rats. 11␤-HSD1 was less active in LH than LL rats: enzyme activities were lower in tissue extracts; urinary cortisone:cortisol was lower in LL rats after cortisone injections; cortisone increased urine volume in LL but not LH rats; and mRNA levels tended to be lower in LH tissues. We conclude that 11␤-HSD1 is impaired in LH rats. The LH phenotype of heavier adrenals, raised corticosterone, and reduced thymus weight is similar to that described for 11␤-HSD1 knockout mice. (Hypertension. 1999;34:1123-1128.)Key Words: glucocorticoids Ⅲ mineralocorticoids Ⅲ corticosterone Ⅲ cortisol Ⅲ cortisone Ⅲ renal function T he Lyon strains of hypertensive (LH), normotensive (LN), and low blood pressure (LL) rats exhibit different patterns of mineralocorticoid and glucocorticoid hormone secretion depending on age. 1 In young LH rats, concentrations of mineralocorticoids (aldosterone and deoxycorticosterone) are elevated, whereas glucocorticoid levels are low in relation to LL or LN rats. In adulthood, the pattern is reversed. Because both mineralocorticoid and glucocorticoid excess can cause hypertension, 2 it may be that these changing patterns of steroid metabolism could account directly for some of the blood pressure differences between Lyon strains of rat.An important factor in the control of corticosteroid metabolism, particularly in relation to the balance between mineralocorticoid and glucocorticoid hormones, is the enzymatic interconversion of biologically active corticosterone (rodent) and cortisol (humans) to the inactive 11-ketone metabolites, 11-dehydrocorticosterone and cortisone, respectively. 3,4 Two distinct isozymes of 11␤-hydroxysteroid dehydrogenase (11␤-HSD1 and 11␤-HSD2) catalyze this reaction. 11␤-HSD2 favo...

11Beta-hydroxysterold dehydrogenase enzymes (11beta-HSD1, 11beta-HSD2) regulate access of adrenocorticosteroids to receptors. 11Beta-HSD2 is a dehydrogenase that protects mineralocorticoid receptors from circulating glucocorticoid hormones, 11beta-HSD1 is a reductase that promotes formation of active hormone in glucocorticoid-sensitive tissues. Here we investigate whether low or high sodium diets affect 11beta-HSD enzyme activities and mRNA expression in liver and kidney tissues. 11Beta-HSD activity was measured as dehydrogenation of 3H-corticosterone by microsomes in the presence of NAD or NADP. In situ hybridisation techniques were used to assess expression of 11beta-HSD1 mRNA (liver and kidney) and 11beta-HSD2 mRNA (kidney). Dietary sodium did not affect 11beta-HSD2 mRNA expression in collecting tubules of the medulla: 11beta-HSD1 mRNA in proximal tubules of the inner cortex/outer medulla was lower after a high sodium diet. 11Beta-HSD1 mRNA in liver was unaffected by treatment. Renal enzyme activity with NAD (11beta-HSD2 cofactor) was lower following a high sodium diet (P < 0.05). In the presence of NADP (11beta-HSD1 co-factor), neither renal nor hepatic activities were affected. Dietary sodium restriction appears to increase 11beta-HSD activity by a non-genomic mechanism; this should enhance aldosterone specificity for mineralocorticoid receptors. 11Beta-HSD1 mRNA expression varies independent of enzyme activity and is not clearly related to altered glucocorticoid activity.