Index >> Rhizobium and Legume Root Nodulation >>Cultural Characteristics

This fact has to be reckoned within any attempt to explain the mode of entry of Rhizobium into legume roots. In general, fast-growing rhizobia such as R. trifolii, R. leguminosarum and R. phaseoli grow vigorously with most sources of carbohydrates. On the other hand, slow-growing rhizobia are more specific in their requirements. They utilize sodium citrate, xylose, mannitol, arabinose, galactose, fructose and rarely dextran.

Vitamin requirements of rhizobia differ among species and strains. Many workers have observed thiamine, biotin and calcium pantothenate requirements for rhizobial growth. However, no growth responses have been observed to nicotinic acid, piridoxin, folic acid, p-aminobenzoic acid, inositol, vitamin B12 and riboflavin. On the other hand, inhibition of growth of R. japonicum by biotin and nicotinic acid has been reported.

Rhizobium cells in clover rhizosphere are small to medium sized (0.5-0.9 × 1.2-3.0 m), Gram-negative rods. They are motile when young and have bi-polar, sub-polar or peritrichous flagella. Cells contain characteristic granules of polymerised B-hydroxybutyrate dry weight) which stain with Sudan Black and appear as highly refractive bodies under phase contrast illumination. Most strains produce gum (extracellular polysaccharide slime) of varying composition. Cell wall of R. trifolii contains glucosamine, muramic acid, glutamic acid, diaminopimelic acid and a wide range of amino acids, characteristic of Gram negative bacteria.