Factors Affecting the Affinity for Oxygen of Cytochrome Oxidases in Hemophilus parainfluenzae

Cold stress induces switchover of respiratory pathway to lactate glycolysis in psychrotrophic Rhizobium strains

Two psychrotrophic strains of Rhizobium, DDSS69, a non-cold acclimated strain, and ATR1, a cold acclimated strain, were subjected to cold stress. A 4-fold increase in the specific activity of lactate dehydrogenase (LDH) was characteristic for cold stressed cells of DDSS69, whereas ATR1 showed a higher LDH activity in general, which increased 1.5-fold under cold stress. Cold sensitive mutants of DDSS69 which could not grow below 15 degrees C, in contrast to the wild type which could grow at 5 degrees C, were isolated using Tn5-tagged mutagenesis. These mutants showed a 40% lower LDH activity than the wild type grown at 5 degrees C that was comparable to the wild type grown at 15 degrees C. High specific activity of succinic dehydrogenase (SDH) at 28 degrees C in both strains and mutants indicated that aerobic respiration via the citrate cycle is the normal mode of saccharide utilization. Shifts to lower temperatures decreased the specific activity of SDH. However, alcohol dehydrogenase (ADH) activity remained very low in both the strains and the mutants at low temperatures indicating that a shift from aerobic saccharide metabolism to anaerobic one under cold stress involves lactate glycolysis rather than alcohol fermentation. There was an increase in membrane-bound ATPase activity under cold stress which is correlated to higher LDH activity. These data show that, in psychrotrophic Rhizobium strains, cold stress induces a switchover of respiratory metabolism from aerobic to anaerobic pathway, especially lactate glycolysis.

SYNTHESIS OF 2-DEMETHYL VITAMIN K2 AND THE CYTOCHROME SYSTEM IN HAEMOPHILUS

White, David C. (University of Kentucky College of Medicine, Lexington). Synthesis of 2-demethyl vitamin K(2) and the cytochrome system in Haemophilus. J. Bacteriol. 89:299-305. 1965.-The synthesis of the respiratory quinone, 2-demethyl vitamin K(2), is stimulated in Haemophilus parainfluenzae under conditions which provoke the synthesis of the cytochrome system. However, the various components of the electron-transport system can be formed in different proportions. The primary flavoprotein dehydrogenases are readily dissociated from the membrane without affecting the content of membrane-bound quinone, cytochrome b(1), or the cytochrome oxidases. These dehydrogenases must be membrane-bound to function, and each can be formed at a different rate. Molar ratios of various constituents of the electron-transport chain were calculated by use of reasonable extinction coefficients for the cytochromes. The molar ratio of quinone to cytochrome c(1) goes from 40 to 3 as the quinone content increases eightfold during the growth cycle. Similarly, the molar ratio of quinone to cytochrome oxidase a(2) varies from 27 to 17, and then increases to 31 as cytochrome oxidase a(1) assumes the oxidase function. The molar ratio of quinone to cytochrome b(1) remains 14 to 1 over a sixfold increase in both components measured in a mutant where cytochrome c(1) does not obscure cytochrome b(1). A similar consistency was noted between the quinone and cytochrome b(1) formation in the hemin-requiring H. influenzae.

Augmented rates of respiration and efficient nitrogen fixation at nanomolar concentrations of dissolved O2 in hyperinduced Azoarcus sp. strain BH72

Azoarcus sp. strain BH72 is an aerobic diazotrophic bacterium that was originally found as an endophyte in Kallar grass. Anticipating that these bacteria are exposed to dissolved O2 concentrations (DOCs) in the nanomolar range during their life cycle, we studied the impact of increasing O2 deprivation on N2 fixation and respiration. Bacteria were grown in batch cultures, where they shifted into conditions of low pO2 upon depletion of O2 by respiration. During incubation, specific rates of respiration (qO2) and efficiencies of carbon source utilization for N2 reduction increased greatly, while the growth rate did not change significantly, a phenomenon that we called "hyperinduction." To evaluate this transition from high- to low-cost N2 fixation in terms of respiratory kinetics and nitrogenase activities at nanomolar DOC, bacteria which had shifted to different gas-phase pO2s in batch cultures were subjected to assays using leghemoglobin as the O2 carrier. As O2 deprivation in batch cultures proceeded, respiratory Km (O2) decreased and Vmax increased. Nitrogenase activity at nanomolar DOC increased to a specific rate of 180 nmol of C2H4 min-1 mg of protein-1 at 32 nM O2. Nitrogenase activity was proportional to respiration but not to DOC in the range of 12 to 86 nM O2. Respiration supported N2 fixation more efficiently at high than at low respiratory rates, the respiratory efficiency increasing from 0.14 to 0.47 mol of C2H4 mol of O2 consumed-1. We conclude that (i) during hyperinduction, strain BH72 used an increasing amount of energy generated by respiration for N2 fixation, and (ii) these bacteria have a high respiratory capacity, enabling them to develop ecological niches at very low pO2, in which they may respire actively and fix nitrogen efficiently at comparatively high rates.

Aspects of helminth metabolism

‘Each organism must be examined as a biochemical entity before any reasonable understanding of helminth metabolism can be attained’ (Saz, 1969).

[Cytochrome pattern of methylotropic acetic acid bacterium MB 58 as dependent on growth conditions]

In contrast to methylotrophic bacteria investigated up to now the facultative methylotrophic Bacterium MB 58 (Acetobactersp. MB 58) does not possess a cytochrome aa3-complex, but we could find out cytochrome, cytochrome cco, cytochrome a1, and moreover cytochrome d in dependence on the growth conditions. Cytochrome d was found only in stationary phase of heterotrophic growth. Under methylotrophic growth conditions cytochrome d could be demonstrated only by lowering of the aeration rate during the fermentation, by variation the pH-value of the growth medium from 4.0 to 6.5 and with low growth rates (low dilution rates) during continuous fermentation. The addition of cyanide to the oxidized suspension of bacteria during the registration of the cytochrome-redox-difference spectrum allowed the selective representation of cytochrome d under all conditions even if no identification was possible in the spectrum normally. The oxidation of cytochrome d of Acetobacter sp. MB 58 in the presence of cyanide is an indication of its cyanide insensitivity. The low level of b-type cytochromes could be represented by a special technique for registration of spectra. In this connection a unknown absorption peak at 570 nm was registered. The cyanide insensitivity of cytochrome d from Acetobacter sp. MB 58 and the occurrence of several terminal oxidases is appreciated as a hint for a branched respiratory chain.

Effects of growth substrate and respiratory chain composition on bioenergetics in Acinetobacter sp. strain HO1-N

The relationship between respiratory chain composition and efficiency of coupling phosphorylation to electron transport was examined in Acinetobacter sp. strain HO1-N. Cells containing only cytochrome o as a terminal oxidase displayed the same stoichiometries of adenosine 5'-triphosphate synthesis and proton extrusion as cells which contained both cytochromes o and d as terminal oxidases. In addition, CO inhibition and photo-relief of cytochromes o or d did not alter the efficiency of energy coupling. These findings indicate that adenosine 5'-triphosphate synthesis is coupled to electron transport through both cytochromes o and d in Acinetobacter.

Influences of growth substrates and oxygen on the electron transport system in Acinetobacter sp. HO1-N

The electron transport system of Acinetobacter sp. HO1-N was studied to determine the specific cytochromes and to measure changes in the composition of the respiratory system due to growth in various concentrations of oxygen or types of growth substrates. Spectrophotometric analysis revealed that the quantity and types of cytochromes changed in response to growth under various concentrations of oxygen. Growth on alkane and nonalkane substrates resulted in only minor differences in cytochrome composition or oxidase activities. Membranes prepared from cells grown under oxygen-limiting conditions contained at least one b-type cytochrome, cytochrome o, cytochrome d, and slight traces of cytochrome a1, whereas membranes prepared from cells grown in the presence of high oxygen concentrations contained only low levels of cytochromes b and o. Polarographic measurements, electron transport inhibitor studies, and photoaction spectrum analyses indicated that cytochromes o, a1, and d were potentially capable of functioning as terminal oxidases in this organism. These experiments also revealed that all three cytochromes may be involved in the oxidation of reduced nicotinamide adenine dinucleotide, succinate, or N,N,N',N'-tetramethyl-p-phenylenediamine.

Inhibition of vitamin K2 and carotenoid synthesis in Staphylococcus aureus by diphenylamine

Diphenylamine at concentrations which did not effect the growth rate inhibited the synthesis of vitamin K(2) in both anaerobic and aerobic cultures by about 50%. At this concentration, diphenylamine inhibited the synthesis of the cyclic carotenoids delta-carotene and the rubixanthins 25 to 35% anaerobically and 60 to 90% aerobically. The inhibition of synthesis of cyclic carotenoids and vitamin K(2) by diphenylamine had no detectable effect on the formation of the membrane-bound electron transport system.

Effect of nitrate, fumarate, and oxygen on the formation of the membrane-bound electron transport system of Haemophilus parainfluenzae

The composition of the membrane-bound electron transport system of Haemophilus parainfluenzae underwent modification in response to the terminal electron acceptor in the growth medium. H. parainfluenzae was able to grow with O(2), nitrate, fumarate, pyruvate, and substrate amounts of nicotinamide adenine dinucleotide (NAD) as electron acceptors. When O(2) served as the electron acceptor and its concentration was lowered below 20 mum, the bacteria formed more cytochromes b, c, a(1), a(2), and o than were present in the cells grown at 150 to 200 mum O(2). Nitrate and nitrite reductase activities also appeared during growth at the low O(2) concentrations in the absence of added nitrate. Cytochrome levels in cells grown anaerobically with fumarate, pyruvate, or NAD as terminal acceptors were similar to those formed in cells grown at low O(2) concentrations. Cells grown with nitrate had higher levels of cytochromes c, b, and o, and of nitrate and nitrite reductases, than did cells grown with the other acceptors. The formation of cytochrome oxidase a(2) was repressed by the presence of nitrate in the growth medium. The critical O(2) concentration (the O(2) concentration at which the rate of O(2) uptake becomes demonstrably dependent on the O(2) concentration) was about 100 mum in cells grown with nitrate and about 15 mum in cells grown with the other acceptors. A mutant of H. parainfluenzae was found to make about 10% as much cytochrome c as the wild type, and its formation of cytochrome a(2) was not repressed by nitrate. The critical O(2) concentration of the mutant was high when it was grown with nitrate, suggesting that the high levels of cytochrome c and the absence of cytochrome a(2) from the wild type are not responsible for the high critical O(2) concentration. The modifications of the respiratory system induced by changing the terminal electron acceptor were inhibited by the presence of chloramphenicol, which suggests that protein synthesis is involved.

Phospholipid metabolism during changes in the proportions of membrane-bound respiratory pigments in Haemophilus parainfluenzae

After a transition from high to low oxygen tension, there was a twofold to 50-fold increase in the content of membrane-bound respiratory pigments of Haemophilus parainfluenzae, and there were concurrent changes in the metabolism of the membrane phospholipids: (i) a twofold decrease in the rate of turnover of the phosphate in all the phospholipids; (ii) a shift from simple one-phase, linear incorporation of phosphate into phospholipids to a complex biphasic incorporation of phosphate into phospholipids; and (iii) an increase in the total phospholipids with a slight increase in the proportion of phosphatidylglycerol (PG) and a slight decrease in the proportion of phosphatidylethanolamine (PE). Changes in the rates of incorporation of phosphate into the phospholipids occurred without a change in the rate of bacterial growth. When the compensatory adjustment of the proportions of the respiratory pigments reached a steady state, the total phospholipid, the rate of incorporation of phosphate into phospholipids, and the proportion of PG fell. At steady-state proportions of cytochromes, the proportion of PE and the rate of turnover of the phosphate in the phospholipids increased. All through an incorporation experiment of 1.5 divisions, the specific activity of the phosphate of PG was twice that of phosphatidic acid (PA). The phosphate of PG turned over 1.2 to 1.5 times more rapidly than the phosphate of PA in cells with high and low cytochrome levels. If the PA was an accurate measure of the precursor for the cytidine-5'-diphosphate-diglyceride, which in turn was the precursor of all the lipids, then the results of these experiments suggested that exchange reactions, in addition to synthesis from PA, were involved in phospholipid metabolism. These reactions were more sensitive to changes in oxygen concentration than was the growth rate.

Cytochrome synthesis and its regulation in Spirillum itersonii

Spirillum itersonii contains b- and c-type cytochromes as well as a carbon monoxide-binding pigment of the cytochrome o type. Synthesis of cytochromes b and c is increased by about two- and fourfold, respectively, when cells are transferred from high to low aeration. The increased concentration of cytochrome is not accompanied by an increase in the respiration rate of the cells. Both cytochrome b and cytochrome c are located in the particulate fraction of cells grown under high or low aeration, and both pigments are fully reducible by succinate. No evidence was found for the accumulation of the protein component of either cytochrome when synthesis of the prosthetic group was limited by iron deficiency, nor did heme or precursors accumulate when protein synthesis was prevented. It was therefore concluded that the formation of the heme prosthetic group is closely integrated with the synthesis of the protein moiety. delta-Aminolevulinate synthase was detected in extracts of the organism. Its activity was correlated with cytochrome synthesis; it was reduced by high aeration and increased under low aeration. The synthase was inhibited by hemin at concentrations of 10 mum or higher. The observations are consistent with a central role for the heme prosthetic group in the regulation of cytochrome synthesis.

Effect of glucose on the formation of the membrane-bound electron transport system in Haemophilus parainfluenzae

The catabolism of glucose by Haemophilus parainfluenzae affected the formation of the primary dehydrogenases of the membrane-bound electron transport system. The formation of other components of the respiratory system, 2-demethyl vitamin K(2), cytochrome b(1), cytochrome c(1), and the cytochrome oxidases a(1), a(2), and o, is not affected by the catabolism of glucose. The formation of all components of the electron transport system is controlled by the identity and concentration of the terminal electron acceptors present in the growth medium.

Formation of a functional electron transport system during growth of penicillin-induced spheroplasts of Haemophilus parainfluenzae

Wright, Elizabeth A. (University of Kentucky College of Medicine, Lexington), and David C. White. Formation of a functional electron transport system during growth of penicillin-induced spheroplasts of Haemophilus parainfluenzae. J. Bacteriol. 91:1356-1362. 1966.-Penicillin in a lactose medium can be used to cause the formation of spheroplasts in Haemophilus parainfluenzae. The resulting spheroplasts grew under conditions which produced rapid formation of the electron transport system in the normal bacteria. The following elements that are incorporated into a functionally active electron transport system were formed in spheroplasts: formate and l-lactate dehydrogenases, 2-demethyl vitamin K(2), cytochromes b(1) and c(1), and the cytochrome oxidases. The catabolic enzymes aldolase, glyceraldehyde-3-phosphate dehydrogenase, and malic dehydrogenase showed slight increases in activity. These experiments indicated that spheroplasts can form a fully functional electron transport system essentially similar to that formed during normal growth. The various components of the electron transport system were formed at different rates in the growing spheroplasts.