Oxidative Phosphorylation in Fractionated Bacterial Systems

Participation of oxygen in the bacterial transformation of 2,4,6-trinitrotoluene

The exposure of Bacillus cereus ZS18 cell suspensions to 2,4,6-trinitrotoluene (TNT) in the absence of other oxidizable substrates increases oxygen uptake, exceeding the basal level of respiration of the bacterium 1.5- and 2-fold with 50 and 100 mg/liter of TNT, respectively. The interaction of both living and to less extent dead bacterial cells with TNT results in the accumulation of superoxide anion (O2*-) in the extracellular medium, which was revealed by the EPR spectroscopy. The accumulation of O2*- decreased by 50-70% in the presence of Cu,Zn-superoxide dismutase of animal origin. In the presence of living bacterial cells, the level of TNT decreased progressively, yielding hydroxylaminodinitrotoluenes together with O2*-. In the presence of heat-killed cells, a moderate decrease in TNT was observed, and the appearance of O2*- was not accompanied by the production of any detectable TNT metabolites. Chelating agents inhibited the transformation of TNT and decreased the formation of O2*-. The demonstrated generation of O2*- during the interaction of TNT with K4[Fe(CN)6] together with the observed effects of chelating agents suggest the participation of iron in the one-electron reduction of TNT and the functioning of an extracellular redox cycle with the involvement of molecular oxygen.

Iron in Neisseria meningitidis: minimum requirements, effects of limitation, and characteristics of uptake

A simple defined medium (neisseria defined medium) was devised that does not require iron extraction to produce iron-limited growth of Neisseria meningitidis (SDIC). Comparison of this medium to Mueller-Hinton broth and agar showed nearly identical growth rates and yields. The defined medium was used in batch cultures to determine the disappearance of iron from the medium and its uptake by cells. To avoid a number of problems inherent in batch culture, continuous culture, in which iron and dissolved oxygen were varied independently, was used. Most of the cellular iron was found to be nonheme and associated with the particulate fraction in sonically disrupted cells. Nonheme and catalase-heme iron were reduced by iron starvation far more than cytochromes b and c and N,N,N',N'-tetramethylphenylenediamine-oxidase. The respiration rate and efficiency also decreased under iron limitation, whereas generation times increased. The iron-starved meningococcus took up iron by an energy-independent system operating in the first minute after an iron pulse and a slower energy-dependent system inhibited by respiratory poisons and an uncoupler. The energy-dependent system showed saturation kinetics and was stimulated nearly fourfold by iron privation. In addition, to determine the availability to the meningococcus of the iron in selected compounds, a sensitive assay was devised in which an iron-limited continuous culture was pulsed with the iron-containing compound.

The role of iron-sulfur center 2 in electron transport and energy conservation in the NADH-ubiquinone segment of the respiratory chain in Paracoccus denitrificans

1. The electron paramagnetic resonance spectra at 15 K of reduced membrane particles of Paracoccus denitrificans exhibit resonance signals with g values, line shapes and temperature profile which are similar to the signals of the iron-sulfur centers observed in the NADH-ubiquinone segment of mitochondrial respiratory chains. These iron-sulfur centers are reducible with NADH, NADPH as well as chemically with dithionite. 2. Sulphate-limited growth of Paracoccus denitrificans results in the loss of an electron paramagnetic resonance signal (gz approximately 2.05, gy approximately gx approximately 1.92) which has properties similar to those of iron-sulfur center 2 of the NADH dehydrogenase of mitochondrial origin. The loss of this signal is accompanied by a decrease in the NADH oxidase and NADH ferricyanide oxidoreductase activities to respectively 30 and 40% of the values found for succinate-limited growth conditions. In addition respiration in membrane particles from sulphate-limited cells loses its sensitivity to rotenone. 3. Since sulphate-limited growth of Paracoccus denitrificans induces loss of site I phosphorylation [Arch. Microbiol. (1977) 112, 25-34] these observations suggest a close correlation between site I phosphorylation, rotenone-sensitivity and the presence of an electron paramagnetic resonance signal with gz approximately 2.05 and gy approximately gx approximately 1.92.

Properties of nonheme iron in a cell envelope fraction from Escherichia coli

The reaction with o-phenanthroline of nonheme iron found in cell envelope fractions from Escherichia coli has been investigated. About 20% of the total nonheme iron reacts directly with o-phenanthroline. This iron appears to be in the ferric state but is reducible by protein sulfhydryl groups in the presence of the chelating agent. A further 20% of the nonheme iron will react with o-phenanthroline only in the presence of dithionite. Succinate can replace dithionite but only produces about 35% of the reaction given by dithionite. The reduction of cytochrome b(1) of the respiratory chain by succinate shows similar behavior to the reaction of iron with o-phenanthroline in the presence of succinate. Both of these components react completely only in the presence of 2-heptyl-4-hydroxyquinoline-N-oxide. The remaining 60% of the nonheme iron of the cell envelope will not react with o-phenanthroline even in the presence of dithionite or 6 m urea. Triton X-100 with dithionite will permit a small part (10%) of this iron to react with o-phenanthroline. The iron which does not react with o-phenanthroline is not associated with succinate, reduced nicotinamide adenine dinucleotide, or d-lactate dehydrogenases.