Rhizobium

Explanation (b) above may of course explain the behavior of group 2, but the whole picture is more consistent with mcplanation (a) in which the nutritional requirements reflect an increasing power to synthesize biotin in proceeding from group 1 to group 3. 

Comparisons of the ability of different strains of the same species to synthesize biotin have been made with other organisms besides Hie Rhizo-bia, and similar differences are implicit from records in the literature. 

---

Although root nodules are the most common sites of N2-fixiag symbioses, some tropical legumes like Sesbania produce stem nodules ia associatioa Jp rhi bium caulinodans (55). la coatrast to root aodules, some stem aodules are photosyathetic and contain, ia the case oiPieschjnomene indica rhizobia themselves capable of photosyathesis (56). This close relatioaship of photosyathesis to fixatioa may ease the eaergy supply demand of nodules. 

NifA proteins are of one of two types. One group consists of 02-sensitive NifA proteins, which are found in the rhizobia Bhodobacter and Ae spirillum. These proteins have a proposed iron-binding motif on a linker between the central and C-terminal domains that may form a redox-sensitive... 

Bacteroid- Altered form of cells of certain bacteria. Refers particularly to the swollen, irregular vacuolated cells of rhizobia in nodules of legumes. 

Moreover, the lipo-chitooligosaccharides, also known as nod factors, permit nitrogen fixation by which plants and symbiotic Rhizobia bacteria can reduce atmospheric nitrogen to the ammonia that is utihzed by the plant, thus making available nitrogen compounds to other living organisms. 

Rhizobia. Taxa belonging to both the genera Rhizobium and Bradyrhizobium are capable of degrading simple aromatic compounds including benzoate (Chen et al. 1984) and 4-hydroxy-benzoate (Parke and Omston 1986 Parke et al. 1991). It has been shown that 4-hydroxyben-zoate hydroxylase is required for the transport of 4-hydroxybenzoate into the cell (Wong et al. 1994). In strains of Rhizobium trifolium, the metabolism of benzoate involves either 3,4-dihydroxybenzoate (protocatechuate) 3,4-dioxygenase (Chen et al. 1984), or catechol... 

Damaj M, D Ahmad (1996) Biodegradation of polychlorinated biphenyls by rhizobia a novel finding. Biochem Biophys Res Commun 218 908-915. 

Rao JR, JE Cooper (1994) Rhizobia catabolize nod gene-inducing flavonoids via C-ring fission mechanisms. J Bacterial 176 5409-5413. 

The most studied molecular cross talk is that between rhizobia and the... 

This chapter considers the various types of root products with a potential functional role in the usually tough environment of soil. Only direct effects of immediate benefit to plant growth—e.g., an increase in nutrient solubility—are considered here. Although root products of a plant species may have a direct effect on important groups of soil organisms, such as rhizobia and mycorrhizae. their effect on the plant is not immediate these and aspects related to microbial activity in the rhizosphere are not considered here (see Chaps. 4, 7, and 10). For an extensive and recent review of the microorganisms in the rhizosphere, the reader is referred to Bowen and Rovira (23). 

Establishment of symbiotic relationships Rhizobia Endomycorrhizae Ectomycorrhizae Chemotactic response... 

Figure 2 Structures of flavonoids present in root exudates of host plants and inducing nod gene expression in rhizobia (1) as 3,5,7,3 -tetrahydroxy-4 -methoxyflavanone, inducer in Rhizohium legiiminosarum bv. viciae (2) as 3, 4, 5, 7-tetrahydroxy-flavone, inducer in Rhizohium melilotr, (3) as 4, 7-dihydroxyisoflavone, inducer in Bradyrhizohium japonicum (4) as couinestrol, intermediate in phenylpropane metabolism, weak inducer. (From Ref. 64.)...

M. Pamiske, B. Ahiborn, and D. Werner, Isoflavonoid-inducible resistance to the phytoalexin glyceollin in. soybean rhizobia. J. Bacterial 173 2222 (1991). 

T. Vallaeys, E. Topp, G. Muyzer, V. Macheret, G. Laguerre, A. Rigaud, and G. Soulas, Evaluation of denaturing gradient gel electrophoresis in the detection of I6S rDNA sequence variation in rhizobia and methanotrophs. FEMS Microbiol. Ecol. 24 279 (1997). 

S. A. Omar and M. H. Abd-Alla, Biocontrol of fungal root rot diseases of crop plants by the use of Rhizobia and Bradyrhizobia. Folia Microbiol. 45 431 (1998). 

E. Fabiano, G. Gualticri, C. Pritsch, G. Polla, and A. Arias, Extent of high-affinity iron tran.sport systems in field isolates of rhizobia. Plant Soil 764 177 (1994). 

J. B. Neilands, Overview of bacterial iron transport and siderophore systems in rhizobia. Iron Chelation in Plants and Soil Microorganisms (L. L. Barton and B. C. Heming, eds.). Academic Press, London, 1993, pp. 179-195. 

---