Effect of temperature and irradiance on the uptake of ammonium and nitrate by <Emphasis Type="Italic">Laurencia brongniartii</Emphasis> (Rhodophyta,Ceramiales)

The effects of temperature (20, 24 and 28 °C) and irradiance (15 and 40 μmol photon m⁻² s⁻¹) on the nitrate and ammonium uptake rates of the subtropical red alga, Laurencia brongniartii, were investigated to prepare for tank cultivation. Nitrate uptake followed saturation kinetics and was faster at higher irradiances and temperatures. In contrast, ammonium uptake was linear over the experimental range and was not affected by an increase in temperature. A parameter, β, was calculated to compare substrate uptake rates of nitrate along the linear portion of the uptake curve with that of ammonium. For nitrate, β was lower at low irradiance and higher at high irradiance (β = 0.007 ± 0.003 and 0.030 ± 0.002 [μmol N L⁻¹ (μmol N g_ww⁻¹ d⁻)⁻¹], respectively). However, β was 0.023 ± 0.002 and 0.034 ± 0.002 [μmol N L⁻¹ (μmol N g_ww⁻¹ d⁻¹)⁻¹] for ammonium, suggesting a preference for ammonium over nitrate.     

Quasi steady state growth of <Emphasis Type="Italic">Lactococcus lactis</Emphasis> in glucose-limited acceleration stat (A-stat) cultures

Quasi steady state growth of Lactococcus lactis IL 1403 was studied in glucose-limited A-stat cultivation experiments with acceleration rates (a) from 0.003 to 0.06 h⁻² after initial stabilization of the cultures in chemostat at D = 0.2–0.3 h⁻¹. It was shown that the high limit of quasi steady state growth rate depended on the acceleration rate used—at an acceleration rate 0.003 h⁻² the quasi steady state growth was observed until μ _crit = 0.59 h⁻¹, which is also the μ _max value for the culture. Lower values of μ _crit were observed at higher acceleration rates. The steady state growth of bacteria stabilized at dilution rate 0.2 h⁻¹ was immediately disrupted after initiating acceleration at the highest acceleration rate studied—0.06 h⁻². Observation was made that differences [Δ(μ − D)] of the specific growth rates from pre-programmed dilution rates were the lowest using an acceleration rate of 0.003 h⁻² (< 4% of preset changing growth rate). The adaptability of cells to follow preprogrammed growth rate was found to decrease with increasing dilution rate—it was shown that lower acceleration rates should be applied at higher growth rates to maintain the culture in the quasi steady state. The critical specific growth rate and the biomass yields based on glucose consumption were higher if the medium contained S ₀ = 5 g L⁻¹ glucose instead of S ₀ = 10 g L⁻¹. It was assumed that this was due to the inhibitory effect of lactate accumulating at higher concentrations in the latter cultures. Parallel A-stat experiments at the same acceleration and dilution rates showed good reproducibility—Δ(μ − D) was less than 5%, standard deviations of biomass yields per ATP produced (Y _ATP), and biomass yields per glucose consumed (Y _XS) were less than 15%.     

Growth kinetics and Pho84 phosphate transporter activity of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> under phosphate-limited conditions

The effect of phosphate (P _i ) concentration on the growth behavior of Saccharomyces cerevisiae strain CEN.PK113-5D in phosphate-limited batch and chemostat cultures was studied. The range of dilution rates used in the present study was 0.08–0.45 h⁻¹. The batch growth of yeast cells followed Monod relationship, but growth of the cells in phosphate-limited chemostat showed change in growth kinetics with increasing dilution rates. The difference in growth kinetics of the yeast cells in phosphate-limited chemostat for dilution rates below and above approximately 0.2 h⁻¹ has been discussed in terms of the batch growth kinetic data and the change in the metabolic activity of the yeast cells. Immunological detection of a C-terminally myc epitope-tagged Pho84 fusion protein indicated derepressive expression of the Pho84 high-affinity P _i transporter in the entire range of dilution rates employed in this study. Phosphate transport activity mediated by Pho84 transporter was highest at very low dilution rates, i.e. 0.08–0.1 h⁻¹, corresponding to conditions in which the amount of synthesized Pho84 was at its maximum.     

Optimization of dilution rate for the production of value added product and simultaneous reduction of organic load from pineapple cannery waste

Candida utiilis NRRL Y-900 was grown on pineapple cannery waste as the sole carbon and energy source in a chemostat at dilution rates ranging between 0.05 and 0.65 h⁻¹ to determine the growth kinetics. The cell yield coefficient varied with dilution rate and a maximum value of 0.662 ± 0.002 g_x/g_carb was obtained at a dilution rate of 0.4 h⁻¹. At steady state, the concentrations of carbohydrate, reducing sugar, and chemical oxygen demand (COD) appeared to follow Monod kinetics. At maximum specific growth rate (μ_max) 0.65 h⁻¹, the saturation constants for carbohydrate, reducing sugar and COD were 0.51 ± 0.02 g_carb/1, 0.046 ± 0.003 g_rs/1, and 1.036 ± 0.001 g_COD/1, respectively. Maximum biomass productivity (Q _{x max}) 2.8 ± 0.03 g_x/1 h was obtained at a dilution rate of 0.5 h⁻¹. At this dilution rate, only 71.0 ± 0.41% COD was removed whereas at a dilution rate of 0.1 h⁻¹, 98.2 ± 0.35% reduction in COD was achieved. At a dilution rate of 0.4 h⁻¹, the optimal yeast productivity and reduction in COD were 2.7 ± 0.13 g_p/1 h, and 84.2 ± 0.42%, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of growth, oxygen uptake, and substrate utilization of wild type and genetically engineeredBurkholderia sp

The gene (vgb) encoding the hemoglobin (VHb) ofVitreoscilla sp. was cloned intoBurkholderia sp. and the effect of VHb on the growth characteristics of genetically engineeredBurkholderia (YV1) were compared with wild typeBurkholderia (R34) using continuous flow reactors (chemostat) at various dilution rates under aerobic conditions. Batch oxygen uptake rate showed that YV1 has much higher oxygen uptake rate than R34 (i.e. 0.63 mg O₂/g biomass/min vs. 1.43 mg O₂/g biomass/min for R34 and YV1 respectively at a dilution rate of 1.2 day⁻¹). Monod parameters, maximum growth rate (μ_max) and half saturation coefficient (K_s) were found to be 7.03 day⁻¹ and 691 mg/L for R34 respectively, compared to 5.49 day⁻¹ and 404 mg/L for YV1 respectively. At low dilution rates (<2.5 day⁻¹), when the substrate is present in low concentrations, the growth yield was much higher in YV1 (0.52) than in R34 (0.37). Although substrate utilization rates were similar between R34 and YV1, the latter showed much higher oxygen uptake rate than did R34 at all dilution rates. When the stability of VHb was tested on agar plates containing 40 μg/L of kanamycin and 100 μg/L of ampicillin,vgb gene containing VHb plasmid in YV1 was stable over 82 days. When survivability under oxygen limited conditions was tested, R34 survived only for 11 days whereas YV1 survived over 25 days in liquid media; in agar plate experiments, R34 did not survive more than 40 days whereas more than 75% of YV1 survived over 110 days.     

Simultaneous utilization of pyridine and fructose by Rhodococcus opacus UFZ B 408 without an external nitrogen source

 A bacterium classified as Rhodococcus opacus, which is able to use pyridine (a potentially growth-inhibiting substrate) as its sole source of carbon, energy and nitrogen, was isolated. In a carbon-limited chemostat culture, the kinetics was determined for growth on both pyridine and a mixture of pyridine and fructose (9 mM/22.15 mM). With growth on pyridine, stable steady states were achieved up to dilution rates of about 0.1 h^-1. A further increase in the dilution rate resulted in the progressive accumulation of pyridine in the culture liquid and the cells were washed out. The maximum specific growth rate (μ_max = 0.23 h^-1) and the K _S value (0.22 mM) for growth on pyridine were determined from the residual pyridine concentrations measured within the range of stable steady states. With growth on the substrate mixture, the specific pyridine consumption rates and the residual pyridine concentrations were lower at similar dilution rates than with growth on pyridine alone, and stable steady states were established at dilution rates of up to 0.13 h^-1. The maximum pyridine degradation rate was enhanced to 270 mg pyridine l^-1 h^-1 compared to 210 mg pyridine l^-1 h^-1with growth on pyridine as a single substrate. An external nitrogen source did not need to be added in the case of growth on the substrate mixture. Fructose was assimilated by means of ammonium released from pyridine. Analysis of the nitrogen balance furnished proof that pyridine is an energy-deficient substrate; pyridine was assimilated and dissimilated at a ratio of 1 mol/0.67 mol respectively. The resulting yield coefficient was about 0.55 g dry weight/g pyridine. Moreover, it was demonstrated that, in regard to the biologically usable energy, 1 mol pyridine corresponds to 0.43 mol fructose. Received: 3 July 1995/Received revision: 19 October 1995/Accepted: 24 October 1995     

Glycolytic pathway and hydrogen yield studies of the extreme thermophile <Emphasis Type="Italic">Caldicellulosiruptor saccharolyticus</Emphasis>

NMR analysis of ¹³C-labelling patterns showed that the Embden–Meyerhof (EM) pathway is the main route for glycolysis in the extreme thermophile Caldicellulosiruptor saccharolyticus. Glucose fermentation via the EM pathway to acetate results in a theoretical yield of 4 mol of hydrogen and 2 mol of acetate per mole of glucose. Previously, approximately 70% of the theoretical maximum hydrogen yield has been reached in batch fermentations. In this study, hydrogen and acetate yields have been determined at different dilution rates during continuous cultivation. The yields were dependent on the growth rate. The highest hydrogen yields of 82 to 90% of theoretical maximum (3.3 to 3.6 mol H₂ per mol glucose) were obtained at low growth rates when a relatively larger part of the consumed glucose is used for maintenance. The hydrogen productivity showed the opposite effect. Both the specific and the volumetric hydrogen production rates were highest at the higher growth rates, reaching values of respectively 30 mmol g⁻¹ h⁻¹ and 20 mmol l⁻¹ h⁻¹. An industrial process for biohydrogen production will require a bioreactor design, which enables an optimal mix of high productivity and high yield.     

Simultaneous utilization of glucose and D-xylose by Candida shehatae in a chemostat

The kinetics of biomass formation, D-xylose utilization, and mixed substrate utilization were determined in a chemostat using the yeast Candida shehatae. The maximum growth rate of C. shehatae grown aerobically on D-xylose was 0.42 h⁻¹ and the Monod constant, K _s, was 0.06 g L⁻¹. The biomass yield, Y _{X/S}, ranged from 0.40 to 0.50 g g⁻¹ over a dilution rate range of 0.2–0.3 h⁻¹, when C. shehatae was grown on pure D-xylose. Mixtures of D-xylose and glucose (∼1 : 1) were simultaneously utilized over a dilution rate from 0.15 to 0.35 h⁻¹ at pH 3.5 and 4.5, but pH 3.5 reduced μ_max and reduced the dilution rate range over which D-xylose was utilized in the presence of glucose. At pH 4.5, μ_max was not reduced with the mixed sugar feed and the overall or lumped K _s value was not significantly increased (0.058 g L⁻¹ vs 0.06 g L⁻¹), when compared to a pure D-xylose feed. Kinetic data indicate that C. shehatae is an excellent candidate for chemostat production of value added products from renewable carbon sources, since simultaneous mixed substrate utilization was observed over a wide range of growth rates on a 1 : 1 mixture of glucose and D-xylose. Received 21 August 1997/ Accepted in revised form 28 May 1998     

Enhanced iturin A production by <Emphasis Type="Italic">Bacillus subtilis</Emphasis> and its effect on suppression of the plant pathogen <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

The behavior of Streptomyces peucetius var. caesius N47 was studied in a glucose limited chemostat with a complex cultivation medium. The steady-state study yielded the characteristic constants μ _max over 0.10 h⁻¹, Y _XS 0.536 g g⁻¹, and m_S 0.54 mg g⁻¹ h⁻¹. The product of secondary metabolism, ɛ-rhodomycinone, was produced with characteristics Y _PX 12.99 mg g⁻¹ and m _P 1.20 mg g⁻¹ h⁻¹. Significant correlations were found for phosphate and glucose consumption with biomass and ɛ-rhodomycinone production. Metabolic flux analysis was conducted to estimate intracellular fluxes at different dilution rates. TCA, PPP, and shikimate pathway fluxes exhibited bigger values with production than with growth. Environmental perturbation experiments with temperature, airflow, and pH changes on a steady-state chemostat implied that an elevation of pH could be the most effective way to shift the cells from growing to producing, as the pH change induced the biggest transient increase to the calculated ɛ-rhodomycinone flux.     

Growth and net photosynthetic rates of <Emphasis Type="Italic">Hosta</Emphasis> ‘blue vision’ during acclimatization in bright,natural light with CO<Subscript>2</Subscript> enrichment

Summary Hosta ‘Blue Vision’, a shade-adapted perennial, was successfully acclimatized in high, natural light conditions in the research Acclimatron^TM at Clemson University, Clemson, SC during the summer of 2000. The supplemental CO₂ levels achieved during acclimatization were 710±113, 2396±121, and 5641±119 μmol mol⁻¹, approximately 2×, 6×, and 15× ambient CO₂. Plants were maintained in H₂O-saturated atmospheres and protected from temperature increases associated with high light intensity. In the 5 wk following ex vitro transfer, plantlet roots grew at the 2× CO₂ level, but shoot biomass was unaffected. Results for the 6× and 15× CO₂ levels were comparable and provided the best plantlet growth. The “doubling time’ that is characteristic of exponential growth was 10.8 and 9.8 d for root and shoot dry weights, respectively. There was no indication of light saturation of net photosynthetic rate (NPR) over the photosynthetic photon flux density (PPFD) range of 100–1200 μmolm⁻²s⁻¹ experienced during this study. An interaction between CO₂ and light intensity levels was detected for NPR of Hosta ‘Blue Vision’ with CO₂ saturation occurring at approximately 2800 μmol mol⁻¹. regardless of light level. Furthermore, at the optimal CO₂ level, NPR increased quadratically as light intensity increased, and NPR was greatest at the maximum light intensity (PPFD: 1200 μmol m⁻²s⁻¹).     

Physiological differences in the growth of <Emphasis Type="Italic">Sargassum horneri</Emphasis> between the germling and adult stages

The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance (10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m⁻²s⁻¹) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m⁻²s⁻¹), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day⁻¹ (25°C, 20 μmol photons m⁻²s⁻¹) and 13% day⁻¹ (8 h daylength). In contrast, the RGRs of the blade weights were 4% day⁻¹ (15°C, 20 μmol photons m⁻²s⁻¹) and 5% day⁻¹ (12 h daylength). Negative growth rates were found at 20 μmol photons m⁻²s⁻¹ of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m⁻²s⁻¹, and 8 h daylength for construction of Sargassum beds and restoration of barren areas.     

Eco-physiological responses of nitrogen-fixing cyanobacteria to light

The eco-physiological responses of three nitrogen-fixing cyanobacteria (N-fixing cyanobacteria), Aphanizomenon gracile, Anabaena minderi, and Ana. torques-reginae, to light were assessed under nutrient saturation. The N-fixing cyanobacteria were isolated into monocultures from a natural bloom in a shallow colored lake and their growth irradiance parameters and pigment composition were assessed. The different ecological traits related to light use (μ_max, α, I _k) suggest that these N-fixing cyanobacteria are well adapted to low light conditions at sufficient nutrients, yet interspecific differences were observed. Aphanizomenon gracile and Anabaena minderi had high relative growth rates at low irradiances (ca. 70% of those in high light), low half saturation constant for light-limited growth (I _k < 9.09 μmol photon m⁻² s⁻¹) and high efficiency (α < 0.11 day⁻¹ μmol photon⁻¹ m² s). Conversely, Ana. torques-reginae showed poorer light competitiveness: low relative growth rates at low irradiances (ca. 40% of those in high light), low α (0.009 day⁻¹ μmol photon⁻¹ m² s) and higher I _k (35.5 μmol photon m⁻² s⁻¹). Final densities in Aphanizomenon gracile and Anabaena minderi reached bloom densities at irradiances above 30 μmol photon m⁻² s⁻¹ with different hierarchy depending on irradiance, whereas Ana. torques-reginae never achieved bloom densities. All species had very low densities at irradiances ≤17 μmol photon m⁻² s⁻¹, thus no N-fixing blooms would be expected at these irradiances. Also, under prolonged darkness and at lowest irradiance (0 and 3 μmol photon m⁻² s⁻¹) akinetes were degraded, suggesting that in ecosystems with permanently dark sediments, the prevalence of N-fixing cyanobacteria should not be favored. All species displayed peaks of phycocyanin, but no phycoeritrin, probably due to the prevailing red light in the ecosystem from which they were isolated.     

Toxicity of dodecylpyridinium and cetylpyridinium clorides against phosphate-accumulating bacterium

The antibacterial effect of cationic surfactants against the pure culture of phosphate (P)-accumulating bacterium Acinetobacter junii was investigated. The estimated EC₅₀ values of the N-dodecylpyridinium chloride (DPC) for growth inhibition was 1.4±0.5 × 10⁻⁶ mol L⁻¹ and for the inhibition of the P-uptake rates 7.3±2.6 × 10⁻⁵ mol L⁻¹. The estimated EC₅₀ values of the N-cetylpyridinium chloride (CPC) for growth inhibition was 4.9±1.3 × 10⁻⁷ mol L⁻¹ and for the inhibition of the P-uptake rates 7.7±2.9 × 10⁻⁶ mol L⁻¹. This suggests the importance of controlling the amounts of cationic surfactants in influent of the wastewater treatment systems in order to avoid the possible failure of the biological P removal from wastewaters.     

Photosynthetic Response of Carrots to Varying Irradiances

Response to irradiance of leaf net photosynthetic rates (P _N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m⁻² s⁻¹ at 20 °C and 350 μmol (CO₂) mol⁻¹(air). The values of P _N were fitted to a rectangular hyperbolic nonlinear regression model. P _N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P _N than CC. None of the cultivars reached saturation at 1 000 μmol m⁻² s⁻¹. The predicted P _N at saturation (P _Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO₂) m⁻² s⁻¹, respectively. The compensation irradiance (I _c) occurred at 54 μmol m⁻² s⁻¹ for Cascade, 36 μmol m⁻² s⁻¹ for CC, 45 μmol m⁻² s⁻¹ for Oranza, and 25 μmol m⁻² s⁻¹ for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO₂) mol⁻¹(PAR) and did not differ. Dark respiration varied from 2.66 μmol m⁻² s⁻¹ for Cascade to 0.85 μmol m⁻² s⁻¹ for RCC. As P _N increased with PAR, intercellular CO₂ decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m⁻² s⁻¹ followed by a steep decline resulting in sharp increases in water use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chemolithoautotrophy and mixotrophy in the thiophene-2-carboxylic acid-utilizing Xanthobacter tagetidis

Xanthobacter tagetidis grew as a chemolithotrophic autotroph on thiosulfate and other inorganic sulfur compounds, as a heterotroph on thiophene-2-carboxylic acid, acetic acid and α-ketoglutaric acid, and as a mixotroph on thiosulfate in combination with thiophene-2-carboxylic acid and/or acetic acid. Autotrophic growth on one-carbon organosulfur compounds, and intermediates in their oxidation are also reported. Thiosulfate enhanced the growth yields in mixotrophic cultures, presumably by acting as a supplementary energy source, since ribulose bisphosphate carboxylase was only active in thiosulfate-grown cells and was not detected in mixotrophic cultures using thiosulfate with thiophene-2-carboxylic acid. Bacteria grown on thiophene-2-carboxylic acid also oxidized sulfide, thiosulfate and tetrathionate, indicating these as possible sulfur intermediates in thiophene-2-carboxylic acid degradation. Thiosulfate and tetrathionate were oxidized completely to sulfate and, consequently, did not accumulate as products of thiophene-2-carboxylic acid oxidation in growing cultures. K _m and V _max values for the oxidation of thiosulfate, tetrathionate or sulfide were 13 μM and 83 nmol O₂ min^–1 (mg dry wt.)^–1, respectively; thiosulfate and tetrathionate became autoinhibitory at concentrations above 100 μM. The true growth yield (Y_max) on thiophene-2-carboxylic acid was estimated from chemostat cultures (at dilution rates of 0.034–0.094 h^–1) to be 112.2 g mol^–1, with a maintenance coefficient (m) of 0.3 mmol thiophene-2-carboxylic acid (g dry wt.)^–1 h^–1, and the maximum specific growth rate (μ_max) was 0.116 h^–1. Growth in chemostat culture at a dilution rate of 0.041 h^–1 indicated growth yields [g dry wt. (mol substrate)^–1] of 8.1 g (mol thiosulfate)^–1, 60.9 g (mol thiophene-2-carboxylic acid)^–1, and 17.5 g (mol acetic acid)^–1, with additive yields for growth on mixtures of these substrates. At a dilution rate of 0.034 h^–1, yields of 57.8 g (mol α-ketoglutaric acid)^–1 and 60.7 g (mol thiophene-2-carboxylic acid)^–1 indicated some additional energy conservation from oxidation of the thiophene-sulfur. SDS-PAGE of cell-free preparations indicated a polypeptide (M _r, 21.0 kDa) specific to growth on thiophene-2-carboxylic acid for which no function can yet be ascribed: no metabolism of thiophene-2-carboxylic acid by cell-free extracts was detected. It was shown that X. tagetidis exhibits a remarkable degree of metabolic versatility and is representative of facultatively methylotrophic and chemolithotrophic autotrophs that contribute significantly to the turnover of simple inorganic and organic sulfur compounds (including substituted thiophenes) in the natural environment. Received: 1 July 1997 / Accepted: 3 November 1997     

Characterization of acclimation of Hordeum vulgare to high irradiation based on different responses of photosynthetic activity and pigment composition

The ability of spring barley (Hordeum vulgare cv. Akcent) to adjust the composition and function of the photosynthetic apparatus to growth irradiances of 25–1200 μmol m⁻² s⁻¹ was studied by gas exchange and chlorophyll a fluorescence measurements and high-performance liquid chromatography. The increased growth irradiance stimulated light- and CO₂-saturated rates of CO₂ assimilation expressed on a leaf area basis up to 730 μmol m⁻² s⁻¹ (HL730), whereas at an irradiance of 1200 μmol m⁻² s⁻¹ (EHL1200) both rates decreased significantly. Further, the acclimation to EHL1200 was associated with an extremely high chlorophyll a/b ratio (3.97), a more than doubled xanthophyll cycle pool (VAZ) and a six-fold higher de-epoxidation state of the xanthophyll cycle pigments as compared to barley grown under 25 μmol m⁻² s⁻¹ (LL25). EHL1200 plants also exhibited a long-term inhibition of Photosystem II (PS II) photochemical efficiency (F _v/F _m). Photosynthetic capacity, chlorophyll a/b and VAZ revealed a linear trend of dependence on PS II excitation pressure in a certain range of growth irradiances (100–730 μmol m⁻² s⁻¹). The deviation from linearity of these relationships for EHL1200 barley is discussed. In addition, the role of increased VAZ and/or accumulation of zeaxanthin and antheraxanthin in acclimation of barley to high irradiance is studied with respect to regulation of non-radiative dissipation and/or photochemical efficiency within PS II. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cell growth and nutritive value of the tropical benthic diatom, <Emphasis Type="Italic">Amphora</Emphasis> sp., at varying levels of nutrients and light intensity,and different culture locations

Two series of experiments were conducted to determine suitable growth factors for the mass propagation of the local algal isolate Amphora sp. A higher growth rate of 0.2 doubling (μ) day⁻¹ was attained at a lower photosynthetic photon flux density (PPFD; 11.4 μmol photon m⁻²s⁻¹) compared to cultures exposed to higher levels of PPFD (16.1 μmol photon m⁻²s⁻¹, −0.1 μ day ⁻¹; 31.3 μmol photon m⁻²s⁻¹, 0.0 μ day⁻¹). Cultures located inside the laboratory had a significantly higher cell density (133 × 10⁴ cells cm⁻²) and growth rate (0.3 μ day⁻¹) compared to those located outdoors (100 × 10⁴ cells cm⁻², 0.2 μ day⁻¹). A comparison of nutrient medium across two locations showed that lipid content was significantly higher in cultures enriched with F/2MTM (macronutrients + trace metals) and F/2MV (macronutrients + vitamins). Saturated fatty acids were also present in high concentrations in cultures enriched with F/2M (macronutrients only). Significantly higher amounts of saturated fatty acids were observed in cultures located outdoors (33.1%) compared to those located indoors (26.6%). The protein, carbohydrates and n-6 fatty acid content of Amphora sp. were influenced by the location and enrichment of the cultures. This study has identified growth conditions for mass culture of Amphora sp. and determined biochemical composition under those culture conditions. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Microgravity effects on thylakoid,single leaf,and whole canopy photosynthesis of dwarf wheat

The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21–24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 μmol m⁻² s⁻¹) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 μmol m⁻² s⁻¹) and CO₂ (4000 μmol mol⁻¹) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at ∼280 μmol m⁻² s⁻¹ were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO₂ compensation (121 vs. 118 μmol mol⁻¹) and PPF compensation (85 vs. 81 μmol m⁻² s⁻¹) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity.     

Microbial sensor system which usesMethylomonas sp. for the determination of methane

Summary Pseudomonas putida (ATCC 111 72) was studied in a continuous culture at various dilution rates with asparagine as the sole carbon source and limiting factor. Under the experimental conditions applied, a considerable number of the cells became attached to the fermentor walls and equipment. The viable count of the attached cells was of the same magnitude as those in suspension. The following steady-state characteristics were obtained: The cell-mass (OD₆₂₀ and dry weight) versus dilution rate (D) had maxima at 0.63 and 1.1 h⁻¹. The corresponding plot of viable count had a minimum at 0.94 h⁻¹ whereafter it reached a maximum at 1.3 h⁻¹. Largest yield coefficient obtained was 0.44 g dry weight/g asparagine (D=1.1 h⁻¹). The productivity of the culture increased with D up to 1.1 h⁻¹, which is far above the D corresponding to the maximum specific growth rate (^μmax) of a batch culture (0.59 h⁻¹). The cell mass was not completly washed-out of the fermentor even at a D of 2.2 h⁻¹. The influence of attached growth for the steady-state characteristics, and the significance of the results in relation to chemostate as an instrument for testing environmental factors, are discussed. It is suggested that the attached cells had a significantly higher (^μmax) value than the suspended ones.     

Physiological characterization and cultivation strategies of the pentachlorophenol-degrading bacteria Sphingomonas chlorophenolica RA2 and Mycobacterium chlorophenolicum PCP-1

The physiological characteristics of growth and pentachlorophenol degradation of the bacteria Sphingomonas chlorophenolica RA2 and Mycobacterium chlorophenolicum PCP-1 were studied quantitatively in liquid culture under various conditions of pH, temperature, pO₂, pCO₂ and PCP concentration. Concerning their metabolic properties, RA2 and PCP-1 can be regarded as r-strategist and K-strategist, respectively. RA2 showed a higher activity concerning growth and PCP degradation than PCP-1 under optimum conditions. However, PCP-1 performed better under extreme conditions. Maximum growth rates or RA2 and PCP-1 on glucose were 0.21 h⁻¹ and 0.024 h⁻¹ and maximum PCP degradation rates 315 and 40 μmol (g of dry cells)⁻¹ h⁻¹, respectively. Optimized cultivation for RA2 on a technical scale led to the production of 40 g L⁻¹ of cell dry mass within 55 h. The cultivation strategy including pH-controlled ammonium feeding can be used to effectively produce sufficient biomass of both strains for both research and application as inoculants in soil clean-up. Received 28 July 1998/ Accepted in revised form 30 November 1998