Energy Production and Growth of Pseudomonas oxalaticus OXl on Oxalate and Formate

The efficiency of oxidative phosphorylation in Pseudomonas oxalaticus during growth on oxalate and formate was estimated by two methods. In the first method the amount of ATP required to synthesize cell material of standard composition was calculated during growth of the organism on either of the two substrates. The [Y2~] theor, values thus obtained were 12,5 and 6.5 for oxalate and formate respectively, if the assumption were made that no energy is required for transport of oxalate or carbon dioxide. When active transport of oxalate requiring an energy input equivalent to 1 mole of ATP per mole of oxalate was taken into account, [Y~]theor. for oxalate was 9.4. True Y ~ values were derived from these data on the assumption that the energy produced in the catabolism of Pseudomonas oxalaticus is used with approximately the same efficiency as in a range of other chemoorganotrophs. P/O ratios were calculated using the equation P/O = YO/YATP. The data for ]1o and me required for these calculations were obtained from cultures of Pseudomonas oxalaticus growing on oxalate or formate in carbon-limited continuous cultures. The P/O ratios calculated by this method were, for oxalate, 1.3 (or 1.0 if active transport were ignored), and for formate, 1,7. in the second method the stoicheiometries of the respiration-linked proton translocations with oxalate and formate were measured in washed suspensions of ceils grown on the two substrates. The --+ H+/O ratios obtained were 4.3 with oxalate and 3.9 with formate. These data indicate the presence of two functional phosphorylation sites in the electron transport chain of Pseudomonas oxalaticus during growth on both substrates. A comparison of the P/O ratio on oxalate obtained with the two methods indicated that the Abbreviations. PMS = phenazinemethosnlphate; DCPIP = 2,6dichlorophenolindophenol; TMPD = N,N,N' ,N' te t ramethylt,4-phenylene-diamine dihydrochloride; SD = standard deviation; PEP = Phosphoenol-pyruvate energy requirement for active transport of oxalate has a major effect on the energy budget of the cell; about 50 ~o of the potentially available energy in oxalate is required for its active transport across the cell membrane. Translocation of formate requires approximately 25 % of the energy potentially available in the substrate. These results offer an explanation for the fact that molar growth yields of Pseudomonas oxalaticus on oxalate and formate are not very different.