Coenzyme Q<Subscript>10</Subscript> production by <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis> in stirred tank and in airlift bioreactor

A higher Coenzyme Q₁₀ (CoQ₁₀) concentration of 25.04 mg/l was found in airlift bioreactor than the value of 18.11 mg/l obtained in stirred tank under the aerobic-dark cultivation of Rhodobacter sphaeroides. Aeration rate didn’t show obvious impact to CoQ₁₀ production in airlift bioreactor. The fed-batch operation in airlift bioreactor could increase the biomass concentration and led to the maximum CoQ₁₀ concentration of 33.91 mg/l measured, but a lower CoQ₁₀ cell content (3.5 mg CoQ₁₀/DCW) was observed in the fed-batch operation as compared to the batch operation. To enhance the CoQ₁₀ content, an aeration-change strategy was proposed in the fed-batch operation of airlift bioreactor. This strategy led to the maximum CoQ₁₀ concentration of 45.65 mg/l, a 35% increase as compared to the simple fed-batch operation. The results of this study suggested that a fed-batch operation in airlift bioreactor accompanying aeration-change could be suitable for CoQ₁₀ production.     

Design and simulation of a fuzzy controller for fed-batch yeast fermentation

In baker's yeast fermentation, the process is non-linear and the response of the system to changes in glucose feeding has a very long delay time. Therefore, a conventional system can not give satisfactory results. In this paper, a fuzzy controller designed to control a fed-batch fermenter is presented. The fuzzy controller uses Respiratory Quotient (RQ) as a controller input and produces glucose feeding rate as control variable. The controller has been tested on a simulated fed-batch fermenter. The results show that the maximum yeast production is possible by keeping the specific growth rate (μ) and the glucose concentration (C _s) at preset values (μ _Cand C _s,c) and minimizing the ethanol production.     

Comparative evaluation of various control schemes for fed-batch fermentation

The crucial problem associated with control of fed-batch fermentation process is its time-varying characteristics. A successful controller should be able to deal with this feature in addition to the inherent nonlinear characteristics of the process. In this work, various schemes for controlling the glucose feed rate of fed-batch baker's yeast fermentation were evaluated. The controllers evaluated are fixed-gain proportional-integral (PI), scheduled-gain PI, adaptive neural network and hybrid neural network PI. The difference between the specific carbon dioxide evolution rate and oxygen uptake rate (Q_c-Q_o) was used as the controller variable. The evaluation was carried out by observing the performance of the controllers in dealing with setpoint tracking and disturbance rejection. The results confirm the unsatisfactory performance of the conventional controller where significant oscillation and offsets exist. Among the controllers considered, the hybrid neural network PI controller shows good performance.     

Thermal clamping of temperature-regulating flowers reveals the precision and limits of the biochemical regulatory mechanism

The flowers of several families of seed plants warm themselves when they bloom. In some species, thermogenesis is regulated, increasing the rate of respiration at lower ambient temperature (T _a) to maintain a somewhat stable floral temperature (T _f). The precision of this regulation is usually measured by plotting T _f over T _a. However, such measurements are influenced by environmental conditions, including wind speed, humidity, radiation, etc. This study eliminates environmental effects by experimentally ‘clamping’ T _f at constant, selected levels and then measuring stabilized respiration rate. Regulating flowers show decreasing respiration with rising T _f (Q ₁₀ < 1). Q ₁₀ therefore becomes a measure of the biochemical ‘precision’ of temperature regulation: lower Q ₁₀ values indicate greater sensitivity of respiration to T _f and a narrower range of regulated temperatures. At the lower end of the regulated range, respiration is maximal, and further decreases in floral temperature cause heat production to diminish. Below a certain tissue temperature (‘switching temperature’), heat loss always exceeds heat production, so thermoregulation becomes impossible. This study compared three species of thermoregulatory flowers with distinct values of precision and switching temperature. Precision was highest in Nelumbo nucifera (Q ₁₀ = 0.16) moderate in Symplocarpus renifolius (Q ₁₀ = 0.48) and low in Dracunculus vulgaris (Q ₁₀ = 0.74). Switching temperatures were approximately 30, 15 and 20°C, respectively. There were no relationships between precision, switching temperature or maximum respiration rate. High precision reveals a powerful inhibitory mechanism that overwhelms the tendency of temperature to increase respiration. Variability in the shape and position of the respiration–temperature curves must be accounted for in any explanation of the control of respiration in thermoregulatory flowers.     

Investigation of the potential of biocalorimetry as a process analytical technology (PAT) tool for monitoring and control of Crabtree-negative yeast cultures

Biological reaction calorimetry, also known as biocalorimetry, has led to extensive applications in monitoring and control of different bioprocesses. A simple real-time estimator for biomass and growth rate was formulated, based on in-line measured metabolic heat flow values. The performance of the estimator was tested in a unique bench-scale calorimeter (BioRC1), improved to a sensitivity range of 8 mW l^− 1 in order to facilitate the monitoring of even weakly exothermic biochemical reactions. A proportional–integral feedback control strategy based on these estimators was designed and implemented to control the growth rate of Candida utilis, Kluyveromyces marxianus and Pichia pastoris by regulating an exponential substrate feed. Maintaining a particular specific growth rate throughout a culture is essential for reproducible product quality in industrial bioprocesses and therefore a key sequence for the step from quality by analysis to quality by design. The potential of biocalorimetry as a reliable biomass monitoring tool and as a key part of a robust control strategy for aerobic fed-batch cultures of Crabtree-negative yeast cells in defined growth medium was investigated. Presenting controller errors of less than 4% in the best cases, the approach paves the way for the development of a generally applicable process analytical technology platform for monitoring and control of microbial fed-batch cultures.     

Effect of growth rate on the production of<Emphasis Type="SmallCaps">l</Emphasis>-proline in the fed-batch culture of<Emphasis Type="Italic">Corynebacterium acetoacidophilum</Emphasis>

Corynebacterium acetoacidophilum RYU3161 was cultivated in al-histidine-limited fed-batch culture. To investigate the effect of cell growth on thel-proline production, 5l fed-batch culture was performed using an exponential feeding rate to obtain the specific growth rates (μ) of 0.04, 0.06, 0.08, and 0.1 h⁻¹. The results show that the highest production ofl-proline was obtained at μ=0.04 h⁻¹. The specificl-proline production rate (Q_p) increased proportionally as a function of the specific growth rate, but decreased after it revealed the maximum value at μ=0.08 h⁻¹. Thus, the highest productivity ofl-proline was 1.66 g L⁻¹ h⁻¹ at μ=0.08 h⁻¹. The results show that the production of L-proline inC. acetoacidophilum RYU3161 has mixed growth-associated characteristics.     

Dynamic microbial response under ethanol stress to monitor <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> activity in different initial physiological states

Dynamic Saccharomyces cerevisiae responses to increasing ethanol stresses were investigated to monitor yeast viability and to optimize bioprocess performance when gradients occurred due to the specific configuration of multi-stage bioreactors with cell recycling or of large volume industrial bioreactors inducing chemical heterogeneities. Twelve fed-batch cultures were carried out with initial ethanol concentrations (P _in) ranging from 5 g l⁻¹ to 110 g l⁻¹ with three different inoculums in different physiological states in terms of viability and quantity of ethanol produced (P _o). For a given initial cell viability of 50%, the time to reach the maximum growth rate and maximum ethanol production rate was dependent on the difference P _in − P _o. Whatever the initial physiological state, when the initial ethanol concentration P _in reached 100 g l⁻¹, the yeasts died. Experimental results showed that the initial physiological state of the yeast was the major parameter to determine, the microorganisms’ capacities to adapt and resist environmental changes.     

Production of tetramethylpyrazine by batch culture of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> with optimal pH control strategy

The effects of initial culture pH ranging from 5.0 to 7.5 on biomass content, precursor 3-hydroxy-2-butanone (HB) accumulation, and 2,3,5,6-tetramethylpyrazine (TTMP) formation by Bacillus subtilis CCTCC M 208157 were investigated in shake flask fermentation. Weak acidic conditions were found to favor cell growth and precursor HB accumulation, while TTMP could be synthesized more efficiently in conditions with initial pH towards neutrality. Batch bioprocess of TTMP fermentation by Bacillus subtilis CCTCC M 208157 at various controlled pH values ranging from 5.5 to 7.0 was then examined in 7.5-l fermentor. The results suggested that optimum pH for cell growth and precursor HB accumulation was 5.5 with maximum cell growth rate (Q _x) and precursor HB accumulation rate (Q _HB) of 0.833 g l⁻¹ h⁻¹ and 1.118 g l⁻¹ h⁻¹, respectively, while optimum pH for TTMP formation was 7.0 with maximum TTMP formation rate (Q _TTMP) of 0.095 g l⁻¹ h⁻¹. A pH-shifted strategy was accordingly developed to improve TTMP production in bioreactor fermentation by shifting the culture pH from 5.5 to 7.0 after 48 h of cultivation. By applying the strategy, final TTMP concentration of 7.43 g l⁻¹ was obtained, being 22.2% greater than that of constant-pH fermentation.     

Reflex bradycardia does not influence oxygen consumption during hypoxia in the European eel (Anguilla anguilla)

Most teleost fish reduce heart rate when exposed to acute hypoxia. This hypoxic bradycardia has been characterised for many fish species, but it remains uncertain whether this reflex contributes to the maintenance of oxygen uptake in hypoxia. Here we describe the effects of inhibiting the bradycardia on oxygen consumption (MO₂), standard metabolic rate (SMR) and the critical oxygen partial pressure for regulation of SMR in hypoxia (Pcrit) in European eels Anguilla anguilla (mean ± SEM mass 528 ± 36 g; n = 14). Eels were instrumented with a Transonic flow probe around the ventral aorta to measure cardiac output (Q) and heart rate (f _H). MO₂ was then measured by intermittent closed respirometry during sequential exposure to various levels of increasing hypoxia, to determine Pcrit. Each fish was studied before and after abolition of reflex bradycardia by intraperitoneal injection of the muscarinic antagonist atropine (5 mg kg⁻¹). In the untreated eels, f _H fell from 39.0 ± 4.3 min⁻¹ in normoxia to 14.8 ± 5.2 min⁻¹ at the deepest level of hypoxia (2 kPa), and this was associated with a decline in Q, from 7.5 ± 0.8 mL min⁻¹ kg⁻¹ to 3.3 ± 0.7 mL min⁻¹ kg⁻¹ in normoxia versus deepest hypoxia, respectively. Atropine had no effect on SMR, which was 16.0 ± 1.8 μmol O₂ kg⁻¹ min⁻¹ in control versus 16.8 ± 0.8 μmol O₂ kg⁻¹ min⁻¹ following treatment with atropine. Atropine also had no significant effect on normoxic f _H or Q in the eel, but completely abolished the bradycardia and associated decline in Q during progressive hypoxia. This pharmacological inhibition of the cardiac responses to hypoxia was, however, without affect on Pcrit, which was 11.7 ± 1.3 versus 12.5 ± 1.5 kPa in control versus atropinised eels, respectively. These results indicate, therefore, that reflex bradycardia does not contribute to maintenance of MO₂ and regulation of SMR by the European eel in hypoxia.     

Ethanol production from sweet sorghum juice in batch and fed-batch fermentations by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations. The optimum initial cell and sugar concentrations in the batch fermentation were 1 × 10⁸ cells ml⁻¹ and 24 °Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y _ps) and productivity (Q _p ) were 100 g l⁻¹, 0.42 g g⁻¹ and 1.67 g l⁻¹ h⁻¹ respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar concentration of 24 °Bx was one-time substrate feeding, where P, Y _ps and Q _p were 120 g l⁻¹, 0.48 g g⁻¹ and 1.11 g l⁻¹ h⁻¹ respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of ethanol concentration and product yield.     

Oxygen evolution from single- and multiple-turnover light pulses: temporal kinetics of electron transport through PSII in sunflower leaves

Oxygen evolution per single-turnover flash (STF) or multiple-turnover pulse (MTP) was measured with a zirconium O₂ analyzer from sunflower leaves at 22°C. STF were generated by Xe arc lamp, MTP by red LED light of up to 18000 μmol quanta m⁻² s⁻¹. Ambient O₂ concentration was 10–30 ppm, STF and MTP were superimposed on far-red background light in order to oxidize plastoquinone (PQ) and randomize S-states. Electron (e⁻) flow was calculated as 4 times O₂ evolution. Q _A → Q _B electron transport was investigated firing double STF with a delay of 0 to 2 ms between the two. Total O₂ evolution per two flashes equaled to that from a single flash when the delay was zero and doubled when the delay exceeded 2 ms. This trend was fitted with two exponentials with time constants of 0.25 and 0.95 ms, equal amplitudes. Illumination with MTP of increasing length resulted in increasing O₂ evolution per pulse, which was differentiated with an aim to find the time course of O₂ evolution with sub-millisecond resolution. At the highest pulse intensity of 2.9 photons ms⁻¹ per PSII, 3 e⁻ initially accumulated inside PSII and the catalytic rate of PQ reduction was determined from the throughput rate of the fourth and fifth e⁻. A light response curve for the reduction of completely oxidized PQ was a rectangular hyperbola with the initial slope of 1.2 PSII quanta per e⁻ and V _m of 0.6 e⁻ ms⁻¹ per PSII. When PQ was gradually reduced during longer MTP, V _m decreased proportionally with the fraction of oxidized PQ. It is suggested that the linear kinetics with respect to PQ are apparent, caused by strong product inhibition due to about equal binding constants of PQ and PQH₂ to the Q _B site. The strong product inhibition is an appropriate mechanism for down-regulation of PSII electron transport in accordance with rate of PQH₂ oxidation by cytochrome b₆f.     

Reaction engineering studies for the production of 2-hydroxyisobutyric acid with recombinant Cupriavidus necator H 16

Recombinant Cupriavidus necator H 16 with a novel metabolic pathway using a cobalamin-dependent mutase was exploited to produce 2-hydroxyisobutyric acid (2-HIBA) from renewable resources through microbial fermentation. 2-HIBA production capacities of different strains of C. necator H 16 deficient in the PHB synthase gene and genetically engineered to enable the production of 2-HIBA from the intracellular PHB precursor (R)-3-hydroxybutyryl-CoA were evaluated in 48 parallel milliliter-scale stirred tank bioreactors (V = 11 mL). The effects of media composition, limitations, pH, and feed rate were studied with respect to the overall process performances of the different recombinant strains. 2-HIBA production was at a maximum at nitrogen limiting conditions and if the pH was controlled between 6.8 and 7.2 under fed-batch operating conditions (intermittent fructose addition). The final concentration of 2-HIBA was 7.4 g L⁻¹ on a milliliter scale. Best reaction conditions identified on the milliliter scale were transferred to a laboratory-scale fed-batch process in a stirred tank bioreactor (V = 2 L). Two different process modes for the production of 2-HIBA, a single-phase and a dual-phase fermentation procedure, were evaluated and compared on a liter scale. The final concentration of 2-HIBA was 6.4 g L⁻¹ on a liter scale after 2 days of cultivation.     

A process for the production of ectoine and poly(3-hydroxybutyrate) by <Emphasis Type="Italic">Halomonas boliviensis</Emphasis>

The paper reports a study involving the use of Halomonas boliviensis, a moderate halophile, for co-production of compatible solute ectoine and biopolyester poly(3-hydroxybutyrate) (PHB) in a process comprising two fed-batch cultures. Initial investigations on the growth of the organism in a medium with varying NaCl concentrations showed the highest level of intracellular accumulation of ectoine (0.74 g L⁻¹) at 10–15% (w/v) NaCl, while at 15% (w/v) NaCl, the presence of hydroxyectoine (50 mg L⁻¹) was also noted. On the other hand, the maximum cell dry weight and PHB concentration of 10 and 5.8 g L⁻¹, respectively, were obtained at 5–7.5% (w/v) NaCl. A process comprising two fed-batch cultivations was developed—the first culture aimed at obtaining high cell mass and the second for achieving high yields of ectoine and PHB. In the first fed-batch culture, H. boliviensis was grown in a medium with 4.5% (w/v) NaCl and sufficient levels of monosodium glutamate, NH₄⁺, and PO₄³⁻. In the second fed-batch culture, the NaCl concentration was increased to 7.5% (w/v) to trigger ectoine synthesis, while nitrogen and phosphorus sources were fed only during the first 3 h and then stopped to favor PHB accumulation. The process resulted in PHB yield of 68.5 wt.% of cell dry weight and volumetric productivity of about 1 g L⁻¹ h⁻¹ and ectoine concentration, content, and volumetric productivity of 4.3 g L⁻¹, 7.2 wt.%, and 2.8 g L⁻¹ day⁻¹, respectively. At salt concentration of 12.5% (w/v) during the second cultivation, the ectoine content was increased to 17 wt.% and productivity to 3.4 g L⁻¹ day⁻¹.     

Influence of feeding conditions on clavulanic acid production in fed-batch cultivation with medium containing glycerol

First, the effect of different levels of nitrogen source on clavulanic acid (CA) production was evaluated in batch cultivations utilizing complex culture medium containing glycerol and three different levels of soy protein isolate (SPI). Cellular growth, evaluated in terms of the rheological parameter K, was highest with a SPI concentration of 30 g.L⁻¹ (4.42 g.L⁻¹ N total). However, the highest production of CA (380 mg.L⁻¹) was obtained when an intermediate concentration of 20 g.L⁻¹ of SPI (2.95 g.L⁻¹ total N) was used. To address this, the influences of volumetric flow rate (F) and glycerol concentration in the complex feed medium (Cs_F) in fed-batch cultivations were investigated. The best experimental condition for CA production was F=0.01 L.h⁻¹ and Cs_F=120 g.L⁻¹, and under these conditions maximum CA production was practically twice that obtained in the batch cultivation. A single empirical equation was proposed to relate maximum CA production with F and Cs_F in fed-batch experiments.     

Efficient conversion of lactic acid to butanol with pH-stat continuous lactic acid and glucose feeding method by Clostridium saccharoperbutylacetonicum

In order to achieve high butanol production by Clostridium saccharoperbutylacetonicum N1-4, the effect of lactic acid on acetone–butanol–ethanol fermentation and several fed-batch cultures in which lactic acid is fed have been investigated. When a medium containing 20 g/l glucose was supplemented with 5 g/l of closely racemic lactic acid, both the concentration and yield of butanol increased; however, supplementation with more than 10 g/l lactic acid did not increase the butanol concentration. It was found that when fed a mixture of lactic acid and glucose, the final concentration of butanol produced by a fed-batch culture was greater than that produced by a batch culture. In addition, a pH-controlled fed-batch culture resulted in not only acceleration of lactic acid consumption but also a further increase in butanol production. Finally, we obtained 15.5 g/l butanol at a production rate of 1.76 g/l/h using a fed-batch culture with a pH-stat continuous lactic acid and glucose feeding method. To confirm whether lactic acid was converted to butanol by the N1-4 strain, we performed gas chromatography–mass spectroscopy (GC-MS) analysis of butanol produced by a batch culture during fermentation in a medium containing [1,2,3-¹³C₃] lactic acid as the initial substrate. The results of the GC-MS analysis confirmed the bioconversion of lactic acid to butanol.     

Controlling the sucrose concentration increases Coenzyme Q10 production in fed-batch culture of <Emphasis Type="Italic">Agrobacterium tumefaciens</Emphasis>

The production yield of Coenzyme Q₁₀ (CoQ₁₀) from the sucrose consumed by Agrobacterium tumefaciens KCCM 10413 decreased, and high levels of exopolysaccharide (EPS) accumulated after switching from batch culture to fed-batch culture. Therefore, we examined the effect of sucrose concentration on the fermentation profile by A. tumefaciens. In the continuous fed-batch culture with the sucrose concentration maintained constantly at 10, 20, 30, and 40 g l⁻¹, the dry cell weight (DCW), specific CoQ₁₀ content, CoQ₁₀ production, and the production yield of CoQ₁₀ from the sucrose consumed increased, whereas EPS production decreased as maintained sucrose concentration decreased. The pH-stat fed-batch culture system was adapted for CoQ₁₀ production to minimize the concentration of the carbon source and osmotic stress from sucrose. Using the pH-stat fed-batch culture system, the DCW, specific CoQ₁₀ content, CoQ₁₀ production, and the product yield of CoQ₁₀ from the sucrose consumed increased by 22.6, 13.7, 39.3, and 39.3%, respectively, whereas EPS production decreased by 30.7% compared to those of fed-batch culture in the previous report (Ha SJ, Kim SY, Seo JH, Oh DK, Lee JK, Appl Microbiol Biotechnol, 74:974–980, 2007). The pH-stat fed-batch culture system was scaled up to a pilot scale (300 l), and the CoQ₁₀ production results obtained (626.5 mg l⁻¹ of CoQ₁₀ and 9.25 mg g DCW⁻¹ of specific CoQ₁₀ content) were similar to those obtained at the laboratory scale. Thus, an efficient and highly competitive process for microbial CoQ₁₀ production is available.     

Transient changes in transpiration, and stem and soil CO2 efflux in longleaf pine (Pinus palustris Mill.) following fire-induced leaf area reduction

In 20-year-old longleaf pine, we examined short-term effects of reduced live leaf area (A _L) via canopy scorching on sap flow (Q; kg H₂O h⁻¹), transpiration per unit leaf area (E _L; mm day⁻¹), stem CO₂ efflux (R _stem; μmol m⁻² s⁻¹) and soil CO₂ efflux (R _soil; μmol m⁻² s⁻¹) over a 2-week period during early summer. R _stem and Q were measured at two positions (1.3-m or BH, and base of live crown—BLC), and R _soil was measured using 15 open-system chambers on each plot. E _L before and after treatment was estimated using Q measured at BLC with estimates of A _L before and after scorching. We expected Q to decrease in scorched trees compared with controls resulting from reduced A _L. We expected R _stem at BLC and BH and R _soil to decrease following scorching due to reduced leaf area, which would decrease carbon supply to the stem and roots. Scorching reduced A _L by 77%. Prior to scorching, Q at BH was similar between scorch and control trees. Following scorching, Q was not different between control and scorch trees; however, E _L increased immediately following scorching by 3.5-fold compared to control trees. Changes in E _L in scorched trees corresponded well with changes in VPD (D), whereas control trees appeared more decoupled over the 5-day period following treatment. By the end of the study, R _stem decreased to 15–25% in scorched trees at both stem positions compared to control trees. Last, we found that scorching resulted in a delayed and temporary increase in R _soil rather than a decrease. No change in Q and increased E _L following scorching indicates a substantial adjustment in stomatal conductance in scorched trees. Divergence in R _stem between scorch and control trees suggests a gradual decline in stem carbohydrates following scorching. The absence of a strong R _soil response is likely due to non-limiting supplies of root starch during early summer.     

Dynamic mathematical models of batch experiments and fed-batch cultures for cyclic adenosine monophosphate production by <Emphasis Type="Italic">Arthrobacter</Emphasis> A302

A glucose utilizing strain, Arthrobacter A302 was used for cyclic adenosine monophosphate (cAMP) production in batch modes. The non-structured model in a 5 l stirred tank bioreactor for understanding, controlling, and optimizing the fermentation process was proposed using the logistic equation for microbial growth, the Luedeking-Piret equation for product formation and Luedeking-Piret-like equation for substrate uptake, respectively. The production of cAMP was a mixed-growth-associated pattern. Based on model prediction, a comparison of calculated value using the parameters evaluated above with another experimental data in 30 l bioreactor was used to test the model. The results predicted from the model were in good agreement with the experimental observations in 30 l bioreactor, which demonstrated that the model might be useful for the development and optimization of production of cAMP in industrial scale. Based on estimated kinetic parameters, three different fed-batch modes, constant rate and intermittent (once and repeated), were adopted in order to obtain more cAMP accumulation. Furthermore, the final production of cAMP reached 11.24 g l⁻¹ after 72 h incubation using three stages feeding strategy. In particular, the cAMP productivity (0.156 g l⁻¹ h⁻¹) was successfully improved by 22.83, 11.43 and 9.86%, respectively, compared with the modes of the batch, constant rate fed-batch and intermittent fed-batch once.     

Toxic effects of antimony on photosystem II of <Emphasis Type="Italic">Synechocystis</Emphasis> sp. as probed by in vivo chlorophyll fluorescence

It has been demonstrated that antimony (Sb) at concentrations ranging from 1.0 to 10.0 mg L⁻¹ inhibits O₂ evolution. Deeper insight into the influence of Sb on PSII was obtained with measurements of in vivo chlorophyll fluorescence. The donor and the acceptor sides of PSII were shown to be the target of Sb. Sb treatment induces inhibition of electron transport from Q_A⁻ to Q_B/Q_B⁻ and accumulation of P₆₈₀⁺. S₂(Q_AQ_B)⁻ charge recombination and oxidation by PQ9 molecules became more important in Q_A⁻ reoxidation as the electron transfer in PSII was inhibited. Sb exposure caused a steady increase in the proportion of PSII_X and PSII_β. These changes resulted in increased fluxes of dissipated energy and decreased index of photosynthesis performance, of maximum quantum yield, and of the overall photosynthetic driving force of PSII.