Respiratory and Nitrogenase Activities of Soybean Nodules Formed by Hydrogen Uptake Negative (Hup−) Mutant and Revertant Strains of Rhizobium japonicum Characterized by Protein Patterns

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Abstract
Rates of respiratory CO2 loss and nitrogenase activities of H2 uptake-negative mutant strains and H2 uptake-positive revertant strains of R. japonicum were investigated. Two-dimensional gel protein patterns of bacteroids formed by inoculation of soybeans (Glycine max L.) with these 2 strains show that they are closely related and revealed only 1 difference between them. On the basis of MW standards, the missing protein spot in the H2 uptake-negative mutant strain could be caused by a failure of the mutant to synthesize hydrogenase. Nodules formed by the H2 uptake-negative mutant strain evolved respiratory CO2 at a rate of .apprx. 10% higher than that of nodules formed by the H2 uptake-positive revertant strain. During short-term experiments employed, rates of C2H2 reduction and 15N2 fixation varied considerably among replicate samples and no statistically significant differences between mutant and revertant strains occurred. Increasing the partial pressure of O2 over nodules significantly decreased the proportion of nitrogenase electrons allocated to H+.