1.The relationship between respiratory chain composition and the efficiency of respiration-linked proton translocation was studied in nine bacterial species of widely differing taxonomic and ecological status.2. All the bacteria investigated contained respiratory chain dehydrogenases, ubiquinone and/or menaquinone, cytochrome b and cytochrome oxidase aa3 and/or 0. In addition, some of these organisms also contained pyridine nucleotide transhydrogenase and/or cytochrome c.3. + H+/O ratios of whole cell suspensions oxidising endogenous substrates were in the approximate range 4-8 .mol H+ translocated per g-atom oxygen consumed. It was concluded from the observed --f H+/O ratios of cells loaded with specific substrates that proton-translocating loops 1 and 2 were present in all of the organisms investigated, but that loops 0 and 3 were dependent upon the presence of pyridine nucleotide transhydrogenase and cytochrome c respectively.4. The wide range in energy conservation efficiency which was observed in these organisms is discussed in relation to their respiratory chain composition and natural habitat.Bacterial respiratory systems are very similar in many respects to those present in the mitochondria of higher organisms. Both are membrane-bound, can contain similar types of respiratory carriers and are capable of conserving energy in a form which subsequently can be used either for ATP synthesis or for driving a variety of energy-requiring processes There is some preliminary evidence which suggests that this efficiency may vary between different organisms and within the same organism during growth under different conditions [4,5,14,15]. Obviously, such variations might reflect the diversity of respiratory carrier composition (and hence molecular organisation) which exists in bacterial systems. In order to test this hypothesis we have investigated the respiratory systems of nine species of bacteria which were selected to cover a wide range of natural habitats and to represent a wide spectrum of respiratory chain composition. The results of these investigations confirm that the efficiency of oxidative phosphorylation varies between these different organisms and is related to differences in their respiratory chain composition. MATERIALS AND METHODS OrganismsThe following organisms were used during this study: Acinetobacter lwoffi 4B, Bacillus megaterium D440, Bacillus subtilis D473, Klebsiella pneumoniae NCTC 5055 (all of which were the gift of the Medical Research Council Microbial Systematics Unit, University of Leicester) ; Escherichia coli W and Pseudomonas ovalis Chester (which were kindly donated by Professor H. L. Kornberg, F.R.S.); Hydrogenomonas eutropha H16 (= Alcaligenes eutrophus H16; ATCC

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1. The respiratory chain energy conservation systems of Bacillus megaterium strains D440 and M have been investigated following growth in batch and continuous culture. Respiratory membranes from these strains contained cytochromes b, aa3, o and b, c, a, o, respecitvely; both readily oxidised NADH but neither showed any pyridine nucleotide transhydrogenase activity. 2. Whole cells of both strains exhibited endogenous leads to H+/O ratios of approximately 4; when loaded with specific substrates the resultant leads to H+/O ratios indicated that proton translocating loops 1 and 2 were present in strain D440 and that loops 2 and 3 were present in strain M. 3. In situ respiratory activities were measured as a function of dilution rate during growth in continuous culture. True molar growth yields with respect to oxygen (Y02) of approximately 50 g cells-mole oxygen-1 were obtained for most of the nutrient limitations employed. Average values for YATP of 12.7 and 10.8 g cells-mole ATP equivalent-1 were subsequently calculated for strains D440 and M respectively. 4. Energy requirements for maintenance purposes were low in energy-limited cultures but were substantially increased when growth was limited by nitrogen source (NH+/4). Under the latter conditions there is probably a partial uncoupling of energy-conserving and energy-utilising processes leading to energy wastage.

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