Cyclic variations of photosynthetic activity under nitrogen fixing conditions in Synchococcus RF-1

When nitrogen fixing cell cultures of Synechococcus RF-1 were subjected to an alternating lightdark regime (12 h:12 h), a cyclic decrease in the photosynthetic oxygen evolution potential was observed during the dark periods. This rhythm of net photosynthesis rate was maintained for at least two days after transition to continuous light. The decrease in net photosynthesis was accompanied by a stimulation of dark respiration. However, the magnitude of oxygen uptake was considerably smaller than the observed decrease in oxygen evolution. The photosynthetic activity of cells taken from the dark period was characterized by (i) a significantly lower quantum yield and (ii) a strong reduction in the light-saturated rate of photosynthesis. Growing the cultures on nitrate or under continuous light completely suppressed this rhythm. Protein synthesis was not necessary for the recovery of the light-saturated rate of photosynthesis during the light period. The cellular content of chlorophyll a and of phycobiliproteins did not vary between light and dark period, indicating that quantitative changes in the composition of the photosynthetic apparatus are not the basis for the observed oscillations. Regulatory modifications of the photosynthetic efficiency are proposed as an adaptation mechanism to adjust the intracellular oxygen concentration to the needs for nitrogenase activity.Abbreviation Chl chlorophyll     

Effects of salinity on photosynthetic characteristics in photomixotrophic cell-suspension cultures from Alternanthera philoxeroides

We studied the effect of NaCl salinity on the development of cellular photosynthesis using a green, photomixotrophic, cell-suspension culture of Alternanthera philoxeroides (Mart.) Griseb. For these cells, increasing the concentration of sucrose in the media produces a rapid drop in net photosynthetic rate, which recovers as sucrose is depleted from the media. This predictable recovery provides a simple system to examine cellular photosynthetic development. Cells, unadapted to high salinity, were transferred to nutrient media with 30 mM sucrose (Control) or nutrient media with 30 mM sucrose and 100 mM NaCl (Salt). A dramatic increase in the dark respiration rate of Control and Salt cells during the first 6 d of the experiment produced net oxygen consumption in the light. The high dark respiration rates during this period were accompanied by a decline in total Chl and the amounts of two photosynthetic proteins, the light harvesting Chl a/b binding protein of photosystem II (LHCP) and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco SSU). The dark respiration rate of Salt cells was greater than that of Control cells on days 4–8. After day 4, dark respiration rates decreased and net photosynthesis increased to stable values in both treatments at day 11 after media sucrose concentration reached a minimum. As dark respiration rates decreased and net photosynthetic rates increased, total Chl and the amounts of LHCP and rubisco SSU increased in both Control and Salt cells. The slower development of photosynthetic capacity in salt cells was correlated with a fresh weight that was 20% lower than that of control cells at the end of the experiment.     

Factors controlling the metabolic response to glucose in isolated rat lung cells

Glucose decreases the oxygen utilization by isolated rat lung cells. Its effect displays saturation type kinetics with a “Ki” of 2.2. mM. The similarity of this value with the reported “Km” of 2.4 mM described for glucose uptake by these cells, suggests that both processes may be intimately related and both of them are under the control of the same rate limiting step. Several arguments point to glucose transport into these cells as the most important rate limiting step for its utilization: 1) Phloridzin prevented glucose inhibition of oxygen uptake while mannoheptulose did not; 2) The activity of hexokinase which is the least active glycolytic enzyme in these cells far exceeded the observed rates of glucose utilization and a decrease of 45 per cent in its activity in starved animals did not affect the rate of glucose uptake; 3) The “Km” of hexokinase for glucose is two orders of magnitude below the observed “Km” for glucose uptake and the “Ki” for glucose inhibition of respiration.     

Light control of the respiration of exogenous glycerol in the red macroalga Grateloupia doryphora

Heterotrophic activity in macroalgae has been little studied, but the red macroalga Grateloupia doryphora is known to grow in light at a higher rate in a glycerol-containing medium than in seawater. The effects of 0·1 M exogenous glycerol in seawater (SW90-gly) on the respiration rate of G. doryphora and the role played by light were investigated. The algae pretreated for 2 h in the light and in SW90-gly evolved oxygen and fixed carbon dioxide (H¹⁴CO₃ ^?), but also evolved radioactive ¹⁴CO₂ from [¹⁴C]glycerol. The rate of oxygen evolution was lower than that of samples in seawater, due to a high respiration rate and/or a partial inhibition of photosynthesis induced by glycerol. In contrast, the rate of inorganic carbon fixation was higher in SW90-gly than in control samples in seawater, suggesting that non-photosynthetic patterns were operating. In darkness, after pretreatment in the light in SW90-gly, samples showed a high oxygen uptake rate just after the light was turned off. Twenty minutes of darkness were enough to decrease this high respiration rate to that of samples in seawater. The oxygen uptake observed in all experiments with glycerol was mitochondrial as it was inhibited by potassium cyanide and salicylhydroxamic acid (SHAM). Pretreatment of samples in the light in SW90-gly with the photosynthetic inhibitor DCMU did not inhibit ensuing dark respiration, thus providing evidence for a non-photosynthetic effect of the light. The highest dark respiration rate was observed after the samples were pretreated in monochromatic blue light in glycerol-containing media.     

Carbon-13 nuclear magnetic resonance spectroscopy of high-spin iron(III) porphyrin compounds

1. There was no apparent correlation between the rate of respiration and rate of accumulation of proline in Candida albicans cells. 2. In contrast to normal cells, the respiration in the starved cells became completely cyanide insensitive. The starvation of cells in the presence of cycloheximide prevented the cells from becoming cyanide insensitive. The addition of Fe(III), however, accelerated the process. 3. Oxidizable substrates e.g. NADH, acetate and glucose, when added to cyanide-insensitive starved cells, exhibited 40--280% stimulation in respiration rate. However, this enhancement in oxidation by various substrates was not coupled to a simultaneous increase in the proline uptake or in intracellular ATP levels. 4. There was 6-fold stimulation in proline uptake when cyanide-insensitive cells were preincubated with 50 mM glucose. The preincubation of starved cells resulted in a partial restoration of cyanide sensitivity and increased intracellular ATP levels. The preincubation of starved cells with other oxidizable substrates resulted in a partial restoration of cyanide sensitivity but had no stimulatory effect on intracellular ATP levels and proline accumulation. 5. Both the enhanced uptake and ATP levels in glucose preincubated cells were found to be completely abolished by iodoacetate. 6. It is proposed that the increased proline uptake in cells preincubated with glucose was mainly due to the production of glycolytic energy.     

HETEROTROPHIC GROWTH OF ULVA LACTUCA (CHLOROPHYCEAE)1

The effect of external glucose (51 mM) and acetate (13 mM) on growth and photosynthetic capacity of Ulva lactuca L. was tested in laboratory cultures over 41 days in the dark and in dim light (0.9 μmol photons·m^?2·s^?1) at 7–8° C. Glucose and acetate had a significant positive effect on growth rate, chlorophyll content, and quantum yield for discs grown in the dark and in dim light. The carbon gain from heterotrophic uptake was low and only allowed U. lactuca to maintain a specific uptake was low and only allowed U. lactuca to maintain a specific growth rate of 0.005 day^?1 compared to 0.06–0.1 day^?1 at higher light intensities. However, plants with added organic substrate maintained a normal chlorophyll content and were able to photosynthesize whereas control plants lost pigmentation and photosynthetic capability after 41 days in both dim light and darkness, probably because of disorganization of the photosynthetic apparatus. This suggest that the ecological significance of heterotrophic uptake is to allow U. lactuca to survive during prolonged low light conditions with an intact photosynthetic apparatus.     

Light-enhanced dark respiration in mesophyll protoplasts from leaves of pea

The respiratory oxygen uptake by mesophyll protoplasts of pea (Pisum sativum cv Arkel) was stimulated up to threefold after 15 minutes of illumination at an intensity of 1250 microeinsteins per square meter per second in the presence of 5 millimolar bicarbonate at 30°C. The extent of light-enhanced dark respiration (LEDR) increased progressively with duration of preillumination. The LEDR exhibited two phases. The initial high rate of respiration decreased in about 10 minutes to a lower steady value similar to that before illumination. The promotion of LEDR by the presence of bicarbonate and inhibition by glyceraldehyde or 3-(3,4-dichlorophenyl)-1,1-dimethylurea suggested that LEDR was dependent on products of photosynthetic carbon assimilation/electron transport. Thus, the photosynthetic products exert a markedly quick influence on dark respiration in mesophyll protoplasts.     

Investigation of the dark metabolism of acetate in photoheterotrophically grown cells ofRhodospirillum rubrum

The mechanism of the aerobic dark assimilation of acetate in the photoheterotrophically grown purple nonsulfur bacteriumRhodospirillum rubrum was studied. Both in the light and in the dark, acetate assimilation inRsp. rubrum cells, which lack the glyoxylate pathway, was accompanied by the excretion of glyoxylate into the growth medium. The assimilation of propionate was accompanied by the excretion of pyruvate. Acetate assimilation was found to be stimulated by bicarbonate, pyruvate, the C₄-dicarboxylic acids of the Krebs cycle, and glyoxylate, but not by propionate. These data implied that the citramalate (CM) cycle inRsp. rubrum cells can function as an anaplerotic pathway under aerobic dark conditions. This supposition was confirmed by respiration measurements. The respiration of cells oxidizing acetate depended on the presence of CO₂ in the medium. The fact that the intermediates of the CM cycle (citramalate and mesaconate) markedly inhibited acetate assimilation but had almost no effect on cell respiration indicated that citramalate and mesaconate were intermediates of the acetate assimilation pathway. The inhibition of acetate assimilation and cell respiration by itaconate was due to its inhibitory effect on propionyl-CoA carboxylase, an enzyme of the CM cycle. The addition of 5 mM itaconate to extracts ofRsp. rubrum cells inhibited the activity of this enzyme by 85%. The data obtained suggest that the CM cycle continues to function inRsp. rubrum cells that have been grown anaerobically in the light and then transferred to the dark and incubated aerobically.     

Polarographische Messung der Nitritreduktion von Chlorella im monochromatischen Licht

Summary In green plant cells nitrite is reduced by two systems, one dependent on photosynthesis and the other upon respiration. Using a polarographic method for continuous measurement of nitrite uptake, the relationship between light driven and respiration linked nitrite reduction of Chlorella cells was studied.Photosynthetic nitrite reduction is characterized by a pronounced increase in the velocity of nitrite uptake upon illumination. After the light is turned off the velocity immediately returns to the preillumination value. Photosynthetic nitrite reduction of Chlorella is separated from respiration linked nitrite reduction by illumination with red light under anaerobic conditions; it is stimulated by CO₂ and is inhibited by DCMU, findings which confirm earlier observations.In white light a special blue light stimulation of nitrite uptake is overlapped by photosynthetic nitrite reduction. In contrast to photosynthetic nitrite reduction this type of light stimulation is characterized by a lag period of about I min from the onset of illumination; it continues about 10 min when the light is turned off. It is separated from photosynthetic nitrite reduction by irradiation of the algae with low intensities of short wavelength light (<500 nm). Blue light stimulation of nitrite uptake of Chlorella is strongly dependent on the developmental stage of the cells. It is observed with young cells (autospores) of synchronized algae only.There is no evidence for any connection between blue light stimulation of nitrite uptake and photosynthesis. From the sensitivity of this process towards anaerobic conditions and antimycin A it is concluded to be a stimulation of respiration linked nitrite reduction.Under conditions of low exogenous nitrite concentration a temporary inhibition of steady state dark nitrite reduction appears immediately after the light is turned off. From several observations it is concluded that the inhibition already exists during the preceding illumination and decreases the rate of total nitrite uptake in the light. This process is suppressed by inhibition of respiration as well as by the inhibitor of photosynthesis, DCMU.If nitrate is the source of nitrogen an excretion of nitrite is found following illumination. The kinetics of this process agree with those observed for the light induced inhibition of steady state dark nitrite reduction immediately after illumination.     

Inhibition of Cyanide-Insensitive Respiration in <Emphasis Type="Italic">Klebsiella oxytoca</Emphasis> SYSU-011 by 8-Hydroxyquinolone

The inhibition of the cyanide (KCN)-insensitive respiration of Klebsiella oxytoca SYSU-011 by 8-hydroxyquinoline (8-HQ) was determined. Results showed that the profile of the rate of oxygen uptake of normal-grown and 8-HQ–grown K. oxytoca SYSU-011 was biphasic and similar, suggesting that 8-HQ did not inhibit the respiration of normal-grown K. oxytoca SYSU-011. A different biphasic KCN inhibition profile of respiration was observed for KCN-grown cells treated with and without 8-HQ. No decrease in respiration rate of KCN-grown cells and a 40% decrease in respiration rate of KCN-grown cells treated with 8-HQ were observed when KCN concentration was 10^–1 mM. Comparing differences of the profiles of oxygen uptake in KCN-grown cells with and without 8-HQ addition indicated that 8-HQ inhibited expression of the KCN-insensitive pathway carried out by nonheme oxidase. Greater inhibition of NADH oxidase activity by 2-n-heptyl-4-hydroxyquinoline-N-oxide from the cell membrane of the KCN-grown cells treated with 8-HQ, and more H₂O₂ production from these cells with than without 8-HQ, suggest that the function of the cyanide-insensitive pathway can stabilize the respiration of the cyanide-grown cells to prevent the production of H₂O₂.     

STUDIES ON PHOTOSYNTHESIS : SOME EFFECTS OF LIGHT OF HIGH INTENSITY ON CHLORELLA

1. The effect on oxygen evolution of Chlorella vulgaris produced by light intensities up to about 40,000 f.-c. has been studied by the use of the Warburg technique. 2. Above a certain critical intensity, which is determined by the previous history of the cells, the rate of oxygen evolution decreases from the maximum to another constant rate. This depression is at first a completely reversible effect. 3. With a sufficiently high intensity this constant rate represents an oxygen uptake greater than the rate of dark respiration. During such a constant rate of oxygen uptake a progressive injury to the photosynthetic mechanism takes place. After a given oxygen consumption the rate falls off, approaching zero, and the cells are irreversibly injured. 4. The constant rate of oxygen evolution (2 and 3) decreases in a continuous manner with increasing light intensities, approaching a value which is approximately constant for all lots of cells regardless of previous history. 5. Two alternative hypotheses have been presented to explain the observed phenomena. The more acceptable of these proposes quick inactivation of the photosynthetic mechanism, the extent of inhibition depending on the light intensity. 6. In Chlorella vulgaris solarization is influenced by the previous history of the cells.     

Salt relations of Dunaliella. Transitional changes in glycerol content and oxygen exchange reactions on water stress

Changes in glycerol content are reported for Dunaliella tertiolecta over an 8 h period after a salt stress or dilution stress. Under the experimental conditions, the new glycerol level was reached in about 30 min in light or dark but there was evidence of oscillations after that, particularly on dilution stress. Glycerol disappearance on dilution stress is caused predominantly by dissimilation. A salt stress immediately inhibited photosynthetic oxygen evolution and caused net oxygen uptake for a period of about 36 h after the stress. Oxygen evolution was reestablished after that and the process of recovery to the point of resumption of net evolution was not affected by conditions designed to inhibit protein synthesis. Dilution stress of comparable magnitude diminished but did not eliminate photosynthetic oxygen evolution and recovery to a pre-stress level took about 18 h. Effects of HCO ₃ ^- concentration suggested that photorespiration was not the sole determinant of oxygen uptake induced by salt stress but it was not possible to apportion with confidence the contribution of mitochondrial and other types of respiration. There was no evidence that modification by stress of energy-induced proton fluxes across the plasma membrane constituted an osmoregulatory signal in either species.     

A re-examination of the problem of photochemical nitrogen reduction by blue-green algae

Summary Although it was possible in the light in the absence of carbon dioxide to obtain a ratio of nitrogen fixed to oxygen evolved in nitrogen-starved cells of A. cylindrica near to 1:1.5, that quoted by other workers, ratios varying between 1:0.9 and 1:3.0 were also obtained. The amount of oxygen evolved under the same conditions by normal cells in the presence of pyruvate was increased considerably. Since the addition of pyruvate also resulted in increased carbon dioxide output in the dark with the same algal material, oxygen output in the light was attributed to the production of factors necessary for carbon assimilation.Addition of pyruvate to nitrogen-starved and normal cells in the light resulted in similar rates of oxygen evolution after an initially higher rate in the starved cells. The ratio of overall nitrogen fixed to oxygen evolved, was 1:6.6 for the starved cells and 1:6.4 for the normal cells, showing that the presence of an added substrate increased oxygen output relative to nitrogen uptake. ¹⁴CO₂ was recovered from sodium pyruvate-1-¹⁴C in flasks incubated in the dark, showing that, at least in the dark, pyruvate was decarboxylated.The interpretation of these results is that endogenous and exogenous substrates available to cells of A. cylindrica become decarboxylated and that, in the light, carbon dioxide produced may be assimilated photochemically with accompanying oxygen evolution. This interpretation has been discussed in relation to reports of photochemical nitrogen reduction in blue-green algae.     

Influence of sodium ion on heavy metal-induced inhibition of light-regulatd proton efflux and active carbon uptake in the cyanobacterium Anabaena flos-aquae

The light-induced proton efflux and active carbon uptake are inhibited by mercury and cadmium ions in Anabaena flos-aquae. The inhibitory effects of these heavy metal ions are reversed by 40 mM concentration of sodium. Here we report that light-induced proton efflux is sodium-dependent which leads to a characteristic enhancement in the rate of photosynthetic oxygen generation and carbon fixation. A low concentration (10 M) of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) significantly inhibited the rate of oxygen generation while 10 M carbonyl cyanide-m-chlorophenylhydrazone (CCCP) completely blocked the oxygen generation activity in the organism. The chlorophyll-a fluorescence yield indicates that little fluorescence quenching occurred in the absence of sodium ion. Increasing the extracellular sodium ion accelerated both the initial rate and the extent of fluorescence quenching. These results support the assumption that metal-induced inhibition of the photosynthetic machinery may be mediated by the movement of protons.     

Effects of respiratory activity on starvation survival of marine vibrios

The marine bacterium Vibrio fluvialis NCTC11328 responded to nutrient depletion by a reduction in cell volume, and this was prevented by conditions that eliminated respiration as a source of energy. Addition of the protonophore, CCCP, removal of oxygen and introduction of mutations leading to defects of the respiratory chain prevented size reduction during periods of nutrient limitation. Further, survival of the wild-type strain during starvation was reduced under anaerobic conditions and survival of respiratory mutants under aerobic conditions was reduced compared with that of the parent strain. Removal by mutation of the respiratory Na⁺ pump from Vibrio alginolyticus did not inhibit size reduction or lead to reduced viability in starved cultures.Abbreviations ANa medium A containing 0.4 M sodium chloride - ANaS ANa containing 50 mM sodium succinate - CCCP carbonyl cyanide-m-chlorophenylhydrazone - CFU colony forming units - FMNH flavine mononucleotide - MMS modified Morita's salts solution - MMSGC MMS containing 20 mM glucose and 0.1% (w/v) casamino acids - MMST MMS buffered to pH 8.5 with 50 mM tricine - NM nutrient Morita's broth - Ox oxidase - DH dehydrogenase - NTG N-methyl-N'-nitro-N-nitrosoguanidine     

Branched respiratory chain in aerobically grown Staphylococcus aureus —oxidation of ethanol by cells and protoplasts

Addition of ethanol and some other primary alcohols, except methanol, to cells and protoplasts (but not membrane particles) considerably stimulated the rate of oxygen consumption. This additional respiration was strongly inhibited by 0.1 mM KCN. The cyanide inhibition curve of endogenous substrate oxidation was slightly biphasic while in the presence of ethanol it became clearly biphasic having K _i values of approx. 0.1 and 0.5 mM. Based on the steady-state cytochrome spectra in the presence of 0.1 mM KCN, we attributed the lower K _i to cytochrome a ₆₀₂. Proteolysis of protoplasts external membrane proteins did not change the rate of endogeneous substrate oxidation but prevented the inhibition of this respiration by low concentrations of KCN and stimulation of oxygen consumption by ethanol. The activity of NAD⁺-dependent ethanol dehydrogenase in the cytoplasm was found to be 520 nmol NADH-x min^–1 x mg^–1 protein. Proteolysis of external membrane proteins apparently inhibits the operation of the cytochrome a ₆₀₂-containing electron transport branch inducing the suppression of electron flow from NADH to oxygen.     

Respiratory inhibition by copper in Tetrahymena pyriformis GL

An excess of copper incorporated into Tetrahymena cells was mainly distributed in mitochondria, and inhibited oxygen uptake of Tetrahymena cells. The inhibition of oxygen uptake was clearly to copper uptake in mitochondria. Succinate was most favorable as a substrate stimulating oxygen uptake in mitochondria, and oxygen uptake was most strongly inhibited by copper (0.1 mM) in the presence of succinate among various substrates. The copper incorporated into mitochondria was in the fraction with the inner membranes. Succinate dehydrogenase (SDH) was inhibited at the lowest copper concentration (0.1 mM) among respiratory related enzymes. The redox potential of respiratory components was raised by copper. These results suggest that respiratory inhibition of Tetrahymena cells by copper may be mainly cause by inhibition of SDH as a FAD-protein and oxidation of electron carriers. At higher copper concentrations, MDH, cytochrome c reductase, and ATP synthesis were also inhibited. Growth inhibition may be due to these effects of copper in mitochondria. Mercury affected both oxygen uptake and SDH more strongly than copper. Zinc (0.1 mM) also affected oxygen uptake in mitochondria and a little in whole cells, however, it did not inhibit SDH. Cobalt, manganese, and nickel affected both oxygen uptake and SDH only a little at the same concentration (0.1 mM) as copper.     

On the nature of the light-induced component of dark respiration of plants

The data on the isotope composition of carbon of CO₂ of the light-induced dark respiration component have been analyzed using the oscillation model of photosynthesis. It was concluded that this component originates during the transformation of sucrose accumulated by the plant in the oxygenase phase of photosynthetic oscillations in the light period into organic acids. The transformation occurs in the dark period. It this process, C-3 and C-4 atoms, which determine the “heavy“ isotope composition of carbon of CO₂ of the light-induced dark respiration component, are split off from the hexose link of sucrose.     

The relationship between energy-dependent phagocytosis and the rate of oxygen consumption in Tetrahymena.

The induction of high rates of food vacuole formation in Tetrahymena pyriformis increased the rate of respiration in exponentially growing cells by 17% and in starving cells by 47.5%. The increased rate of oxygen uptake was caused by phagocytosis itself, as shown by comparing the rates of respiration of a Tetrahymena mutant exposed to particles at the permissive or restrictive temperatures for food vacuole formation. During cell division, heat-synchronized cells in rich, particle-supplemented medium showed a significant decrease in the rate of respiration. Furthermore, dimethyl sulphoxide, in concentrations sufficient to block food vacuole formation, suppressed the rate of respiration to a level similar to that of starved cells. Cytochalasin B, fowever, did not reduce the rate of oxygen uptake despite the inability of the cells to complete the formation of food vacuoles during treatment; a possible explanation for this finding is discussed. There was a strong correlation between formation of food vacuoles and a high metabolic rate in Tetrahymena.     

On the significance of electron transport systems for growth of Rhodospirillum rubrum

The inhibitory effects of 2-hydroxybiphenyl on various electron transport reactions of isolated membranes and growth in the presence of malate of either phototrophic or chemotrophic cells of Rhodospirillum rubrum were studied. 50% inhibition of both oxygen uptake of whole cells and growth under chemotrophic conditions (i.e. aerobiosis in the dark) was achieved in the presence of 0.09 mM 2-hydroxybiphenyl. With isolated membranes the same effect on NADH oxidase was obtained with 0.08 mM of inhibitor. Succinate dependent respiratory reactions were inhibited by 50% at a concentration of 0.36 mM. Growth under phototrophic conditions (i.e. anaerobiosis in the light) was inhibited by 50% in the presence of 0.17 mM (wild type strain) or 0.21 mM (blue-green mutant, strain VI) of 2-hydroxybiphenyl. Photophosphorylation and light dependent NAD⁺ reduction by succinate were inhibited by 50% at concentrations of 0.21 mM and 0.03 mM of inhibitor, respectively. After phototrophic growth of the organisms for about five doublings of cell mass in the presence of 0.18 mM of 2-hydroxybiphenyl coloured carotenoids could no longer be detected. Membrane fractions of such cultures exhibited normal activities of succinate cytochrome c reductase but activities of NADH cytochrome c reductase were decreased by 80%. In comparison with a blue green mutant, strain VI, of R. rubrum light induced absorbance changes at 865 nm as well as activities of photophosphorylation were unaffected. However, no activity of light dependent NAD⁺ reduction with succinate could be detected. The data indicate that cellular respiration as well as chemotrophic growth depend largely on NADH dependent respiration. Phototrophic growth, on the other hand, is limited by photophosphorylation while energy dependent reversed electron flow to NAD⁺, if at all, is of rathe minor importance.Abbreviation BChl bacteriochlorophyll