Influence of phosphorus concentration on the growth kinetics and stoichiometry of the microalga Scenedesmus obliquus

The growth of the freshwater microalga Scenedesmus obliquus was studied at 30°C in a mineral culture medium with phosphorus concentrations of between 0 and 372 μ . The values for the specific growth rates, between and , fitted a semistructured substrate-limitation model with μ_m1 = 0·0466 h⁻¹, μ_m2 = 0·0256 h⁻¹ and . The specific uptake rate of phosphorus reached a maximum value of q_Sm1 = 658·01 × 10⁻⁴ μmol P mg⁻¹ biomass h⁻¹.     

Production d'NH4 par la crevette Crangon crangon L. dans deux écosystémes côtiers. approche expérimentale et étude de l'influence du sédiment sur le taux d'excrétion

Estimation of the ammonia production of the shrimp C. crangon in two littoral ecosystems (oligotrophic sand and eutrophic mud) was determined in winter and summer conditions from laboratory observations in experimental microcosms. The ammonia excretion rate of C. crangon was not influenced by either the sediment type or the ammonia concentration of the overlying water; on the other hand, the mean excretion rate and the response to initial handling stress increased markedly as shrimp were deprived of soft substratum.

The daily ammonia production of C. crangon was 16 μmol NH₃ · g ⁻¹ wet wt · day ⁻¹ in winter and 40 μmol in summer. A gross production of 12 μmol NH₃ · m⁻² · day ⁻¹ and 300–700 μmol μ m⁻² · day⁻¹, respectively, could be expected in the two ecosystems studied. This would account for 5% (winter) and 2–4% (summer) of the total NH⁺₄ flux at the sediment-water interface. The contribution of the excretion of all macrofauna to the NH⁺₄ flux from the sediment is discussed.     

Growth and photosynthesis of Hydrocotyle ranunculoides L. fil. in Central Europe

Floating Pennywort (Hydrocotyle ranunculoides L. fil.) is a worldwide distributed aquatic plant. The species is native to North America and quite common also in Central and South America. In Europe, Japan and Australia it is known as an alien plant, sometimes causing serious problems for affected ecosystems and human use of water bodies. Starting from Western Europe with an eastwards directed spread, Floating Pennywort was recorded in Germany in 2004 for the first time. Since then, the species spread out and got established in western parts of Central Europe. For a definite prediction of the potential of a further spread, data about biology, in particular growth and photosynthesis are needed. Here, regeneration capacity, growth at different nutrient availabilities and photosynthesis of H. ranunculoides were investigated. In addition biomass samples were taken in the field. Results show an enormous regeneration capacity (e.g., by forming new shoots from small shoot fragments), increasing growth rates under increasing nutrient availability and a maximum increase of biomass reaching 0.132±0.008 g g⁻¹ dw d⁻¹. Dense populations of H. ranunculoides growing in ponds and oxbows were found at high nutrient content of the substrate, the biomass reaching there up to 532.4±14.2 g dw m⁻². Gas exchange analysis showed a physiological optimum of H. ranunculoides CO₂ uptake at temperatures between 25 and 35 °C and high photon flux densities (PPFD) above 800 μmol photons m⁻² s⁻¹. In comparison, native Hydrocotyle vulgaris showed an optimum of net photosynthesis at 20–30 °C and a light saturation of CO₂ gas exchange at 350 μmol photons m⁻² s⁻¹.     

Biochemical and biophysical studies on cytochrome aa3 VIII. Effect of cyanide on the catalytic activity

1. 1. Cyanide inhibits the catalytic activity of cytochrome aa₃ in both polarographic and spectrophotometric assay systems with an apparent velocity constant of 4·10³ M⁻¹·s⁻¹ and a K_i that varies from 0.1 to 1.0 μM at 22 °C, pH 7·3.

2. 2. When cyanide is added to the ascorbate-cytochrome c-cytochromeaa₃−O₂ system a biphasic reduction of cytochrome c occurs corresponding to an initial K_i of 0.8 μM and a final K_i of about 0.1 μM for the cytochrome aa₃−cyanide reaction.

3. 3. The inhibited species (a²+a₃³⁺HCN) is formed when a²⁺a₃³⁺ reacts with HCN, when a²⁺a₃²⁺HCN reacts with oxygen, or when a³⁺a₃³⁺HCN (cyano-cytochrome aa₃) is reduced. Cyanide dissociates from a²⁺a₃³⁺HCN at a rate of 2·10⁻³ s⁻¹ at 22 °C, pH 7.3.

4. 4. The results are interpreted in terms of a scheme in which one mole of cyanide binds more tightly and more rapidly to a²⁺a₃³⁺ than to a³⁺a₃³⁺.

Growth and biochemical characterization of microalgal biomass produced in bubble column and airlift photobioreactors: studies in fed-batch culture

Relatively large (0.19 m column diameter, 2 m tall, 0.06 m³ working volume) outdoor bubble column and airlift bioreactors (a split-cylinder and a draft-tube airlift device) were compared for monoseptic fed-batch culture of the microalga Phaeodactylum tricornutum. The three photobioreactors produced similar biomass versus time profiles and final biomass concentration (4 kg m⁻³). The maximum specific growth rate observed within a daily illuminated period in the exponential growth phase, had a value of 0.08 h⁻¹ on the third day of culture. Because of night-time losses of biomass, the specific growth rate averaged over the 4-days of exponential phase was 0.021 h⁻¹ for the three reactors.

The biomass in the vertical column reactors did not experience photoinhibition under conditions (photosynthetically active daily averaged irradiance value of 1150±52 μE m⁻² s⁻¹) that are known to cause photoinhibition in conventional thin-tube horizontal loop reactors. Because of good gas-liquid mass transfer, the dissolved oxygen concentration in the reactors at peak photosynthesis remained <120% of air saturation; thus, oxygen inhibition of photosynthesis and photo-oxidation of the biomass did not occur. Carbohydrate accumulation (up to 13% w/w) by the biomass was favored during light-limited linear growth. A declining light intensity caused a more than five-fold increase in cellular carotenoids but the chlorophylls increased only by about 2.5-fold during the course of the culture. In the stationary phase, up to 2% of the biomass was chlorophylls and carotenoids constituted up to 0.5% of the biomass dry weight.     

Specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana under medium duration light/dark cycles: 13–87 s

The specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana decreased under square-wave light/dark cycles of medium duration, 13–87 s, in comparison to continuous illumination. Three experiments were done in three different turbidostats at saturating and sub-saturating light intensities during the light period, 240–630 μmol m⁻² s⁻¹. Within each experiment the light intensity during the light periods of the intermittent light regimes was equal and this intensity was also applied under continuous illumination. The specific growth rate decreased proportional or more than proportional to the fraction of time the algae were exposed to light; this light fraction ranged from 0.32 to 0.88. We conclude that under these light regimes the chlorophyta C. reinhardtii and C. sorokiniana are not able to store light energy in the light period to sustain growth in the dark period at the same rate as under continuous illumination. C. reinhardtii increased its specific light absorbing surface by increasing its chloropyll-a content under light/dark cycles of 13 s duration and a light fraction of 0.67 at 240 μmol m⁻² s⁻¹; the chloropyll-a content was twice as high under intermittent illumination in comparison to continuous illumination. The combination of a higher specific light absorption together with a lower specific growth rate led to a decrease of the yield of biomass on light energy under intermittent illumination.     

Biochemical and biophysical studies on cytochrome c oxidase XIV. The reaction with cytochrome c as studied by pulse radiolysis

1. The reduction of cytochrome c oxidase by hydrated electrons was studied in the absence and presence of cytochrome c.

2. Hydrated electrons do not readily reduce the heme of cytochrome c oxidase. This observation supports our previous conclusion that heme a is not directly exposed to the solvent.

3. In a mixture of cytochrome c and cytochrome c oxidase, cytochrome c is first reduced by hydrated electrons (k = 4 · 10¹⁰ M⁻¹ · s⁻¹ at 22 °C and pH 7.2) after which it transfers electrons to cytochrome c oxidase with a rate constant of 6 · 10⁷ M⁻¹ · s⁻¹ at 22 °C and pH 7.2.

4. It was found that two equivalents of cytochrome c are oxidized initially per equivalent of heme a reduced, showing that one electron is accepted by a second electron acceptor, probably one of the copper atoms of cytochrome c oxidase.

5. After the initial reduction, redistribution of electrons takes place until an equilibrium is reached similar to that found in redox experiments of Tiesjema, R. H., Muijsers, A. O. and Van Gelder, B. F. (1973) Biochim. Biophys. Acta 305, 19–28.     

Effects of temperature, irradiance, and daylength on the marine diatom Leptocylindrus danicus Cleve. IV. Growth

Growth and dark respiration rates of the marine diatom Leptocylindrus danicus Cleve were measured in axenic batch culture under 49 combinations of temperature (5, 10, 15, 20°C), daylength(15:9, 12:12, 9:15 LD), and irradiance (at least four irradiances per daylength). Cell division rates exhibited a temperature-dependent daylength effect. Optimal temperatures occurred between 15 and 20°C. Both the initial slope () and the growth rate at light saturation (μ_max) were strongly influenced by temperature; increased five-fold and μ_max by an order of magnitude between 5 and 20°C. The compensation irradiance (I_c) was independent of temperature. μ_max was 2.7 div day⁻¹ at 20°C, 2.6 at 15°C, 1.1 at 10°C, and 0.3 at 5 °C. Cells grown under 15:9 and 12:12 LD exhibited similar growth-light curves at 20°C and at 15°C. μ_max of cells grown under 9:15 LD at these temperatures were substantially lower than μ_max under longer daylengths. Growth at 10 and 5°C was independent of daylength.

Dark respiration rates were a linear function of cell division rates at 10, 15, and 20°C, and support the concept that growth rate is dependent on dark respiration rate. These relationships were not influenced by daylength. A detectable relationship between dark respiration and growth at 5°C was not observed.

Photosynthesis and excretion showed temperature-dependent curvilinear relationships with growth rate, reflecting the lower saturation irradiance for growth compared to light saturation of photosynthesis and excretion. The relationship between Chl a-specific photosynthesis and growth was controlled by the C:Chl a ratio, which showed a positive correlation with cell division rate. At 15 and 20°C, light saturation of growth was associated with C:Chl a ratios of 40 to 60; at 5 and 10°C, cells growing at μ_max contained C:Chl a in ratios of 80 to 110.     

Morphological and physiological responses of canola (Brassica napus) siliquas and seeds to UVB and CO2 under controlled environment conditions

Combined effects of UVB radiation and CO₂ concentration on plant reproductive parts have received little attention. We studied morphological and physiological responses of siliquas and seeds of canola (Brassica napus L. cv. 46A65) to UVB and CO₂ under four controlled experimental conditions: UVB radiation (4.2 kJ m⁻² d⁻¹) with ambient level of CO₂ (370 μmol mol⁻¹) (control); UVB radiation (4.2 kJ m⁻² d⁻¹) with elevated level of CO₂ (740 μmol mol⁻¹); no UVB radiation (0 kJ m⁻² d⁻¹) with ambient level of CO₂ (370 μmol mol⁻¹); and no UVB radiation (0 kJ m⁻² d⁻¹) with elevated level of CO₂ (740 μmol mol⁻¹). UVB radiation affected the outer appearance of siliquas, such as colour, as well as their anatomical structures. At both CO₂ levels, the UVB radiation of 4.2 kJ m⁻² d⁻¹ reduced the size of seeds, which had different surface patterns than those from no UVB radiation. At both CO₂ levels, 4.2 kJ m⁻² d⁻¹ of UVB decreased net CO₂ assimilation (A_N) and water use efficiency (WUE), but had no effect on transpiration (E). Elevated CO₂ increased A_N and WUE, but decreased E, under both UVB conditions. At both CO₂ levels, the UVB radiation of 4.2 kJ m⁻² d⁻¹ decreased chlorophyll fluorescence, total chlorophyll (Chl), Chl a and Chl b, but had no effect on the ratio of Chl a/b and the concentration of UV-screening pigments. Elevated CO₂ increased total Chl and the concentration of UV-screening pigments under 4.2 kJ m⁻² d⁻¹ of UVB radiation. Neither UVB nor CO₂ affected wax content of siliqua surface. Many significant relationships were found between the above-mentioned parameters. This study revealed that UVB radiation exerts an adverse effect on canola siliquas and seeds, and some of the detrimental effects of UVB on these reproductive parts can partially be mitigated by CO₂.     

Ontogenetic photosynthetic changes, dispersal and survival of Thalassia testudinum (turtle grass) seedlings in a sub-tropical lagoon

Northward expansion of Thalassia testudinum (turtle grass) in Laguna Madre is occurring faster than can be explained by rhizome growth. We hypothesized that seedling establishment can account for the measured rates of meadow expansion and that seedling carbohydrate reserves are utilized until the plant is photosynthetically self-sufficient. To address seedling establishment, we estimated seed output, seedling dispersal and survival. Carbon dynamics were calculated from measurements of biomass allocation, non-structural carbohydrate carbon reserves and photosynthetic parameters in relation to T. testudinum seedling age. Potential seed production calculated for 1996 was consistent with field observations and was estimated at 66±14 seeds m⁻² bare area. Fruits can be positively buoyant for up to 10 days, while seeds were generally buoyant for <1 day. Water current measurements, made at about the time of seed release, indicate a positive net transport of 1.5 km d⁻¹ to the north. Seedling survival in laboratory culture after 6 months was 96% compared to 11% in the field after 1 year. The average root:rhizome+seed:leaf ratio changed from 0:11:1 for a 1 week old plant to 1:3:1 for a 15 month old plant. Seedlings used to determine whole plant photosynthesis ranged in age from about 1 week (0.25 months) to 15 months. Gross P_max increased from 80 to 220 μmol O₂ gdw sht⁻¹ h⁻¹, while whole plant respiration decreased from 170 to 60 μmol O₂ gdw sht⁻¹ h⁻¹. As the photosynthetic parameters changed, the average non-structural carbohydrate carbon (NSCC) reserves of the seeds decreased from 24 to 3.0 mg NSCC plant⁻¹. Subsequent increases in NSCC were the result of rhizome development. Daily carbon balance, assessed using H_sat periods of 8–18 h d⁻¹, predicts that T. testudinum seedlings become photosynthetically self-sufficient between 2 and 6 months. The unique characteristics of T. testudinum, including seed buoyancy, high seed production and survival rates, coupled with ontogenetic changes in carbon allocation and production imply that sexual reproduction can be important in the long distance dispersal and colonization for this species.     

Photosynthetic photon flux effects on bean response to nitrogen dioxide

Phaseolus vulgaris L. cv. Kinghorn Wax seedlings, supplied with nutrient solution containing either 0 or 5 mM nitrate as sole N source, were exposed to 0.25 μl/l NO₂ for 6 hr each day for 10 days at continuous photosynthetic photon flux (PPF) of 100, 300, 500 or 700 μmol m⁻² sec⁻¹. There was a significant interaction of PPF and nitrate. Shoot and root dry weights increased with increasing PPFs only when nitrate was supplied. The main effects of NO₂ on plant growth were significant; none of the interactions involving NO₂ were significant. Exposure to NO₂ decreased shoot and root dry weight in both the presence and absence of nutrient N and at all PPF levels. All interactions were significant for in vitro leaf nitrate reductase activity (NRA), which increased markedly at PPFs above 100 μmol m⁻² sec⁻¹ when nitrate was supplied. Treatment with NO₂ strongly inhibited enzyme activity in the presence of nitrate, particularly at the 300 μmol m⁻² sec⁻¹ PPF level. These experiments demonstrated that PPF level does not modify the effect of NO₂ on growth but does have a major effect on NRA and on NO₂ effects on NRA in the presence of nutrient nitrate.     

Diurnal light curves and landscape-scale variation in photosynthetic characteristics of Thalassia testudinum in Florida Bay

When using pulse-amplitude modulated (PAM) fluorometry to measure landscape-scale photosynthetic characteristics, diurnal variations in fluorescence during sampling may confound the assessment of the physiological condition. In this study, two photophysiological assessment techniques: Diurnal Yield and Diurnal Rapid Light Curve (RLC) were investigated in an attempt to incorporate the temporal and spatial scales of sampling into a physiological assessment of Thalassia testudinum in Florida Bay. Photosynthesis–irradiance (P–E) curves were calculated using both methods and the ability of each to predict the relationship between relative electron transport rates and irradiance was assessed. Both methods had limitations in providing consistent estimates of photosynthetic efficiency or capacity. The Diurnal Yield method produced unrealistically high predictions of photosynthetic capacity (relative electron transport rate (rETR_max), 417–1715) and saturation irradiance (I_k, 1045–4681 μmol photons m⁻² s⁻¹). In contrast, the Diurnal RLC method generally produced predictions of rETR_max (100–200) and I_k (300–500 μmol photons m⁻² s⁻¹) which were similar to average values calculated from each day's RLCs. The Diurnal RLC method was unable to predict photosynthetic efficiency () only when ambient irradiances were continuously >I_k during the sampling period. We believe that with sampling modifications in high-light or shallow environments, such as starting sampling earlier in the morning, extending sampling later in the day, or using the average from each day's RLCs, that the Diurnal RLC method can produce representative estimates of rETR_max, , and I_k, providing a method to characterize seagrass photosynthesis at the landscape-level. The Diurnal RLC method does not negate Diurnal variation but it produces a curve that incorporates the changing ambient light environment into the assessment of seagrass physiological status.     

Transpiration rates of the understory annual Impatiens capensis (Balsaminaceae) in response to the autumnal changes in canopy leaf area

Leaf transpiration rates of Impatiens capensis were measured beneath a broadleaved deciduous forest canopy over successive growing seasons using a steady-state porometer. The transpiration measurements, which continued into early autumn, provided a framework for assessing whether I. capensis exhibits stomatal opening in response to the autumnal increase in available direct-beam radiation reaching the forest floor. The deciduous canopy LAI (leaf area index) decreased from a growing season maximum of 3.94 m² m⁻², while the understory I. capensis population located along a stream channel maintained LAI values ranging from 0.58 to 1.05 m² m⁻² late into the growing season. Late morning and early afternoon leaf transpiration rates during the months of June and July averaged about 8 μg cm⁻² s⁻¹, with a mean stomatal conductance of 0.5 cm s⁻¹. In August, leaf transpiration averaged almost 12 μg cm⁻² s⁻¹, with stomatal conductance exceeding 1.5 cm s⁻¹. However, beginning in early to mid-September, before canopy leaf-fall, the persistent green leaves of I. capensis exhibited a sharp decline in transpiration, possibly a result of decreasing vapor pressure deficits or non-lethal physiological damage induced by cold stress. This physiological decline offsets any advantage that could have been gained by the increased exposure to direct-beam radiation after canopy leaf-fall in mid-October. Although green leaf area and seed-bearing capsules may persist until the first frost in October or early November, there is no evidence of stomatal opening suggestive of carbon assimilation for enhanced seed development during this early autumn period. We conclude that the persistent green leaf area of I. capensis fails to exploit the increase in available direct-beam radiation in the final stage of its life cycle.     

Actual and potential dark respiration rates and different electron transport pathways in freshwater aquatic plants

The rates of respiratory O₂ uptake have been studied in leaves, stems and whole shoots of several freshwater plants: 6 angiosperms, 2 bryophytes and one alga. For angiosperm leaves, rates varied widely with species (30–142 μmol O₂ (gDW)⁻¹ h⁻¹), were correlated with chlorophyll content and were higher than those of the stems (13–71 μmol O₂ (gDQ)⁻¹ h⁻¹). The rates for the shoots of bryophytes (53–66 μmol O₂ (gDW)⁻¹ h⁻¹) and for the alga Cladophora glomerata (L.) Kütz. (96 μmol O₂ (gDW)⁻¹ h⁻¹) were slightly higher than those of most angiosperm stems, but lower than those for most leaves.

These plants had a significant cyanide-resistant respiration, suggesting the existence of an alternative pathway to the “classic” cytochrome system. This pathway was found to be active in all the species studied, as judged by responses to a specific inhibitor, SHAM (salicylhydroxamic acid). Measurement of electron-transport system (ETS) activity showed that there is a large electron-transport capacity which is not normally used by respiration in vivo.     

The respiratory chain of Azotobacter vinelandii II. The effect of cyanide on cytochrome d

1. Cyanide causes a slow disappearance of the oxidized band (648 nm) of cytochrome d in particles of Azotobacter vinelandii and inhibits the appearance of the reduced band (631 nm). No effect of cyanide is found on the reduced band of cytochrome d.

2. The kinetics of the disappearance of the 648-nm band of cytochrome d with excess cyanide deviates from first-order kinetics at lower temperatures (22 °C) indicating that at least two conformations of the enzyme are involved. At higher temperatures (32 °C) the observed kinetics of the cyanide reaction are first order with a k_on = 0.7 M⁻¹·s⁻¹ and with an estimated k_off of approximately 5·10⁻⁵ s⁻¹.

3. The value of the k_off (7·10⁻⁴−14·10⁻⁴ s⁻¹ at 32 °C) determined from the rate of reduction of cyanocytochrome d by Na₂S₂O₄ or NADH is one order of magnitude larger than the k_off value found when the enzyme is in its oxidized state.

4. No effect of cyanide is found on the spectrum of cytochrome a₁.     

Monitoring of phosphorus bioavailability in water by an immobilized luminescent cyanobacterial reporter strain

Massive growth of cyanobacteria, known as ‘algal blooms’, has become a major concern for water monitoring. It has been observed that environmental factors like temperature, light, and certain patterns of availability of nutrients such as P, N, Fe influence cyanobacterial proliferation and toxin production. In order to monitor nutrients in aquatic ecosystems, an assay for monitoring phosphorus bioavailability to cyanobacteria was developed. The test consists of an immobilized luminescent reporter strain of Synechococcus PCC 7942, designated APL. The reporter strain harbours the gene coding the reporter protein luciferase from Vibrio harveyi under control of the inducible alkaline phosphatase promoter from Synechococcus PCC 7942, and can be induced under phosphorus limitation. The resultant CyanoSensor detects PO₄³⁻−P in a concentration range of 0.3–8 μM after a sample incubation time of 8 h under continuous illumination (50 μE m⁻² s⁻¹). The sensor also responded to a variety of organic phosphorus sources and was storable for 3 weeks at 4 °C. It could be demonstrated that the CyanoSensor for bioavailability monitoring is an improvement to conventional phosphorus detection methods.     

Rate of electron transfer between plastocyanin, cytochrome ƒ, related proteins and artificial redox reagents in solution

The rate of electron transfer between reduced cytochrome ƒ and plastocyanin (both purified from parsley) has been measured as k = 3.6 · 10⁷ M⁻¹ · s⁻¹, at 298 °K and pH 7.0, with activation parameters ΔH^‡ = 44 kJ · mole⁻¹ and ΔS^‡ = +46 J · mole⁻¹ · °K⁻¹. Replacement of cytochrome ƒ with red algal cytochrome c-553, Pseudomonas cytochrome c-551 and mammalian cytochrome c gave rates at least 30 times slower: k = 5 · 10⁵, 7.5 · 10⁵ and 1.0 · 10⁶ M⁻¹ · s⁻¹, respectively.

Similar measurements made with azurin instead of plastocyanin gave k = 6 · 10⁶ and approx. 2 · 10⁷ M⁻¹ · s⁻¹ for reaction of reduced azurin with cytochrome ƒ and algal cytochrome respectively.

Rate constants of 115 and 80 M⁻¹ · s⁻¹ were found for reduction of plastocyanin by ascorbate and hydroquinone at 298 °K and pH 7.0. The rate constants for the oxidation of plastocyanin, cytochrome ƒ, Pseudomonas cytochrome c-551 and red algal cytochrome c-553 by ferricyanide were found to be between 3 · 10⁴ and 8 · 10⁴ M⁻¹ · s⁻¹.

The results are discussed in relation to photosynthetic electron transport.     

Nutrient removal by thermophilic Fischerella (Mastigocladus laminosus) in a simulated algaculture process

A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l⁻¹ daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec⁻¹ m⁻²) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO₃⁻ + NO₂⁻−N, 71% of NH₃-N, 82% of PO₄³⁻ −P, and 70% of total P from effluent water samples containing approximately 400 μg l⁻¹ combined N and 60 μg l⁻¹ P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO₃⁻ + NO₂⁻ removal, 38–45% P removal and no net NH₃ removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling.     

The nitrilases of Rhodococcus rhodochrous NCIMB 11216

Rhodococcus rhodochrous NCIMB 11216 grows on propionitrile or benzonitrile as the sole source of carbon and nitrogen. The possibility that different nitrile-hydrolyzing enzymes were produced under these two growth conditions was investigated. Nitrilase activity in whole cell suspensions from either bacteria grown on propionitrile or benzonitrile were capable of biotransforming a wide range of nitriles. The propionitrile-induced nitrile degrading activity hydrolyzed 3-cyanobenzoate and both the nitrile groups in 1,3-dicyanobenzoate. In contrast, the benzonitrile-induced activity hydrolyzed only one of the nitrile groups in 1,3-dicyanobenzoate, but did not affect 3-cyanobenzoate. Both nitrilases biotransformed -cyano-o-tolunitrile to produce 2-cyanophenylacetic acid. The nitrilases were purified by fast protein liquid chromatography and the -terminus of each enzyme sequenced. SDS-PAGE analysis identified a subunit molecular weight of 45.8 kDa for each nitrilase. The -terminal sequences showed significant similarity with other sequenced nitrilases and with the exception of a single amino acid were identical with each other. Both nitrilases had temperature and pH optima of 30°C and 8.0, respectively. The propionitrile-induced nitrilase had a K_m for benzonitrile of 20.7 m and a V_max of 12.4 μmol min⁻¹ mg⁻¹ protein whereas the benzonitrile-induced nitrilase had a K_m for benzonitrile of 8.83 m and a V_max of 0.57 μmol min⁻¹ mg⁻¹ protein.     

Trapping, loss and annihilation of excitations in a photosynthetic system: II. Experiments with the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas capsulata

In this paper a number of experiments with the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas capsulata is described in which the total fluorescence yield and/or the total fraction of reaction centers closed after a picosecond laser pulse were measured as a function of the pulse intensity. The conditions were such that the reaction centers were either all in the open or all in the closed state before the pulse arrived. These experiments are analysed using the theoretical formalism discussed in the preceding paper (Den Hollander, W.T.F., Bakker J.G.C., and Van Grondelle, R., Biochim. Biophys. Acta 725, 492–507). From the experimental results the number of connected photosynthetic units, λ, the rate of energy transfer between neighboring antenna molecules, k_h, and the rate of trapping by an open reaction center, k^o_t, can be estimated. For R. rubrum it is found that λ = 14−17, k_h = (1−2)·10¹² s⁻¹ and k^o_t = (4−6)·10¹¹ s⁻¹, for Rps. capsulata λ ≈ 30, k_h ≈ 4·10¹¹ s⁻¹ and k^o_t ≈ 3·10¹¹ s⁻¹. The findings are discussed in terms of current models for the structure of the antenna and the kinetic properties of the decay processes occurring in these purple bacteria.