Glucose catabolism in two derivatives of a Rhizobium japonicum strain differing in nitrogen-fixing efficiency

Abstract

Radiorespirometric and enzymatic analyses reveal that glucose-grown cells of R. japonicum isolates I-110 and L1-110, derivatives of R. japonicum strain 3I1b110, possess an active tricarboxylic acid cycle and metabolize glucose by simultaneous operation of the Embden-Meyerhof-Parnas and Entner-Doudoroff pathways. The hexose cycle may play a minor role in the dissimilation of glucose. Failure to detect the NADP dependent decarboxylating 6-phosphogluconate dehydrogenase (EC 1.1.1.44) evidences the absence of the pentose phosphate pathway. Transketolase and transaldolase reactions enable R. japonicum to produce the precursors for purine and pyrimidine biosynthesis from fructose-6-phosphate and glyceraldehyde-3-phosphate. A constitutive NAD-linked 6-phosphogluconate dehydrogenase was detected. The enzyme is stimulated by mannitol or fructose and might initiate a new catabolic pathway. R. japonicum isolate I-110, characterized by shorter generation times on glucose and greater N-fixing efficiency, oxidizes glucose more extensively than type L1-110 and utilizes preferentially the Embden-Meyerhof-Parnas pathway, but the Entner-Doudoroff pathway apparently predominates in type L1-110.