Sugar Metabolism and the Symbiotic Properties of Carbohydrate Mutants of Rhizobium leguminosarum

Abstract

Rhizobium leguminosarum metabolizes sugars via the Entner-Doudoroff and pentose phosphate pathways but does not have a functional Embden-Meyerhof pathway. Although some sugar catabolizing enzymes are constitutive, activities of the ‘Entner-Doudoroff’ enzymes vary with the carbon source. Bacteroids have complete pathways for sugar catabolism even though the specific activities of some enzymes, e.g., glucokinase, are lower than in free-living cells. Tn5-induced mutants lacking glucokinase, fructokinase and pyruvate dehydrogenase have been isolated. Although these mutants are unable to utilize sugars, they all nodulate peas and fix N2. The capacity to utilize particular C6 and C12 sugars is apparently not essential for bacteroid development or the establishment of effective N2 fixation.