The influence of the tension of oxygen on the respiration of rhizobia

Summary

Cultures of Rhizobium trifolii, Rh. leguminosarum, Rh. meliloti and Rh. japonicum were grown in the Novy-Soule type of respiration apparatus and the oxygen consumed, CO ₂ produced and glucose fermented determined. From these data the respiratory quotient, the percentage of glucose used, and the carbon of the glucose used that appeared as CO₂-carbon were calculated. Since very little acids or neutral products are formed by these organisms, the carbohydrate destroyed and not appearing as CO₂ is a measure of gum production by the organisms.

With Rh. trifolii, Rh. leguminosarum and Rh. meliloti, the glucose used, the rate of respiration, and to some extent the glucose that appeared as CO₂, increase with increasing p _O2. About 60 to 80 per cent of the carbon in the glucose utilized appears in the CO₂ produced. All of these cultures had an R. Q. close to unity which was independent of the p _O2. The respiratory quotient of Rh. leguminosarum was inclined to be erratic.

With Rh. japonicum, the rate of respiration, total oxygen consumed, and total CO₂ produced were much lower than the values observed for the other cultures, Also the glucose used increased with decreasing p _O2. The apparatus used was not sufficiently sensitive to detect marked differences in the rate of respiration under the various tensions of oxygen with this organism, but there appeared to be a small increase in the rate of respiration with the higher tensions of oxygen.

With all organisms, excellent fermentation of glucose with a high conversion into CO₂ was observed under low tensions of oxygen (five per cent or less), provided the absolute quantity of this gas was present in excess of the requirements of the organisms.