Uptake and Metabolism of Carbohydrates by Bradyrhizobium japonicum Bacteroids

Open Access
Publisher Website
Google Scholar
Abstract
Bradyrhizobium japonicum bacteroids were isolated anaerobically and were supplied with 14C-labeled trehalose, sucrose, UDP-glucose, glucose, or fructose under low O2 (2% in the gas phase). Uptake and conversion of 14C to CO2 were measured at intervals up to 90 minutes. Of the five compounds studied, UDP-glucose was most rapidly absorbed but it was very slowly metabolized. Trehalose was the sugar most rapidly converted to CO2, and fructose was respired at a rate at least double that of glucose. Sucrose and glucose were converted to CO2 at a very low but measurable rate (2 at a rate 30 times greater than the conversion of carbon Number 6 to CO2, indicating high activity of the pentose phosphate pathway. Enzymes of the Entner-Doudoroff pathway were not detected in bacteroids, but very low activities of sucrose synthase and phosphofructokinase were demonstrated. Although metabolism of sugars by B. japonicum bacteroids was clearly demonstrated, the rate of sugar uptake was only 1/30 to 1/50 the rate of succinate uptake. The overall results support the view that, although bacteroids metabolize sugars, the rates are very low and are inadequate to support nitrogenase.