Sulfide utilization by the photosynthetic bacterium Chlorobium phaeobacteroides

Sulfide and sulfur are used by the photosynthetic bacterium Chlorobium phaeobacteroides as electron donors. Sulfide and sulfur consumption was found to be affected by sulfide concentration in the medium. Raising the sulfide concentration from 0.28 mM to 5.05 mM caused an increase in the amount of S⁼ utilized per growth unit from 0.58 mM to 2.32 mM. This increase in sulfide utilization was not reflected in a higher photosynthetic activity. Sulfide and sulfur consumption was also influenced by light intensity, with higher light intensity sulfide consumption was increased. In Lake Kinneret, Chlorobium phaeobacteroides did not bloom in the thermocline layer until sulfide concentrations reached 0.03–0.06 mM.     

Resource recovery from low strength wastewater in a bioelectrochemical desalination process

In this research, low strength synthetic wastewaters with chemical oxygen demand less than 300 mg L^?1 were treated at different concentrations in a bioelectrochemical desalination process. A process optimization model was utilized to study the performance of the photosynthetic bioelectrochemical desalination process. The variables include substrate (chemical oxygen demand) concentration, total dissolved solids, and microalgae biomass concentration in the cathode chamber. Relationships between the chemical oxygen demand concentration, microalgae, and salt concentrations were evaluated. Power densities and potential energy benefits from microalgal biomass growth were discussed. The results from this study demonstrated the reliability and reproducibility of the photosynthetic microbial desalination process performance followed by a response surface methodology optimization. This study also confirms the suitability of bioelectrochemical desalination process for treating low substrate wastewaters such as agricultural wastewaters, anaerobic digester effluents, and septic tank effluents for net energy production and water desalination.     

Short-term spatial and temporal variation of sediment oxygen dynamics in a tropical tidal salt flat

Short-term spatial and temporal heterogeneity of oxygen dynamics and net primary production were studied in a tree day diurnal variation at a tidal tropical salt flat in the estuarine system of Sepetiba/Guaratiba coastal plain, Rio de Janeiro, Brazil. Oxygen concentrations were measured in situ with high temporal and spatial resolution oxygen microsensors. The results showed a remarkable heterogeneity of both oxygen penetration depth (from 0.18 to 0.85 cm) and net primary production (from −0.085 to 0.115 μmol O₂ cm⁻² s⁻¹) at different stations and sampling periods. Fast variations in abiotic factors like salinity and light due to the variable rainy weather were possibly the drivers of the high heterogeneity. In conclusion, short-term temporal changes could have a remarkable influence in sediment microalgae primary production. Not considering these changes can lead to wrong conclusions concerning the role and importance of sediment microalgae on tidal salt flats.     

Mathematical modeling of biological sulfide removal in a fed batch bioreactor

In this study, biological sulfide removal is investigated in a fed batch bioreactor. In this process, sulfide is converted into elemental sulfur particles as an intermediate in the oxidation of hydrogen sulfide to sulfate. The main product is sulfur at low dissolved oxygen or at high sulfide concentrations and also more sulfates are produced at high dissolved oxygen. According to the carried out reactions, a mathematical model is developed. The model parameters are estimated and the model is validated by comparing with some experimental data. The results show that, the proposed model is in a good agreement with experimental data. According to the experimental result and mathematical model, sulfate and sulfur selectivity are sensitive to the concentration of dissolved oxygen. For sulfide concentration 0.2 (mM) in the bioreactor and dissolved oxygen of 0.5 ppm, only 10% of sulfide load is converted to sulfate, while it is 60% at the same sulfide concentration and dissolved oxygen of 4.5 ppm. At high sulfide load to the bioreactor, the concentration of uneliminated sulfide increases; it leads to more sulfur particle selectivity and consequently, less sulfate selectivity.     

Short-term evaluation of the photosynthetic activity of an alkaliphilic microalgae consortium in a novel tubular closed photobioreactor

A novel lab-scale tubular closed photobioreactor was developed and used for the assessment of the photosynthetic activity of an alkaliphilic microalgae mixed consortium under non-substrate limitation (i.e., bicarbonate excess), controlled irradiance, and mixing conditions. Two prominent haloalkaliphilic strains were identified as members of the consortium: Halospirulina sp. and Picochlorum sp. The photobioreactor (vol?=?0.5 L) consists of two interconnected U-shaped borosilicate glass tubes (internal diameter 2 cm) reaching a surface/volume ratio of 200 m² m^?3. This configuration specifically addressed the issue of the homogeneous light distribution among the microalgae suspended cells cultured by using fixed equidistant cool white light LEDs nearby the surface of the glass tubes. A soft homogeneous pneumatic mixing (i.e., airlift) was implemented in the culture fostering Reynolds numbers around 3000. The photosynthetic activity of the microalgae consortium was evaluated during different short-term kinetic assays by fitting the dynamics of the dissolved oxygen concentration to an oxygenic kinetic model. The photobioreactor operated in a closed loop allowed to control the produced oxygen by the extraction of the cumulated gas in the headspace. The use of this novel photobioreactor allowed the photosynthetic activity of microalgae suspended cells to be assessed, where the dissolved oxygen concentration and irradiance were the main parameters affecting the oxygenic rates under alkaline pH.     

Long-term biological hydrogen production by agar immobilized Rhodobacter capsulatus in a sequential batch photobioreactor

In this study, agar immobilization technique was employed for biological hydrogen production using Rhodobacter capsulatus DSM 1710 (wild type) and YO3 (hup-mutant) strains in sequential batch process. Different agar and glutamate concentrations were tested with defined nutrient medium. Agar concentration 4% (w/v) and 4 mM glutamate were selected for bacterial immobilization in terms of rate and longevity of hydrogen production. Acetate concentration was increased from 40 to 60—100 and 60 mM gave best results with both bacterial strains immobilized in 4% (w/v) agar. Cell concentration was increased from 2.5 to 5 mg dcw mL⁻¹ agar and it was found that increasing cell concentration of wild-type strain caused decrease in yield and productivity while these parameters improved by increasing cell concentration of mutant strain. Also, the hydrogen production time has extended from 17 days up to 60 days according to the process conditions and parameters. Hydrogen production by immobilized photosynthetic bacteria is a convenient technology for hydrogen production as it enables to produce hydrogen with high organic acid concentrations comparing to suspended cultures. Besides, immobilization increases the stability of the system and allowed sequential batch operation for long-term application.

     

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Salt Stress Induces Increase in Starch Accumulation in Duckweed (Lemna aequinoctialis,Lemnaceae): Biochemical and Physiological Aspects

In this study, antioxidant processes were searched for in macrophyte duckweed to investigate tolerance mechanisms in this species against oxidative damage caused by salinity stress. Biochemical and histological analyses were performed on four Lemna aequinoctialis clones grown in Schenk-Hildebrandt medium, 0.5 × SH, supplemented with 1% sucrose liquid medium containing or not containing NaCl in different NaCl concentrations (0, 25 and 50 mM). For most clones, the salt stress effects caused growth inhibition and antioxidant responses at 50 mM NaCl. Also, starch and reducing sugar accumulations were increased with salt, whereas the photosynthetic pigment content was reduced in clone L. aequinoctialis 5569. The plant growth inhibition reflects the oxidative stress shown by the significant increase in malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content. In the L. aequinoctialis 5568 clone, with the highest MDA levels, no antioxidant enzymatic activity was observed. The L. aequinoctialis 5570 clone presented higher ascorbate peroxidase and catalase activities in parallel, indicating that the efficiency of the defence mechanism relies on synchrony between such enzyme activities toward successive elimination of reactive oxygen species and resulting in the assurance of some level of protection of the metabolism from oxidative damage. Considering the moderate salt stress (25 mM), the maintenance of MDA content and small growth inhibition associated with the high starch production suggested the acclimation efficiency of L. aequinoctialis 5570 and 5567 clones, indicating that they may be suitable for cultivation under moderate saline conditions, serving as biofuel feedstock. In addition, this study demonstrates great intraspecific phenotypic plasticity of duckweed, L. aequinoctialis, from closely related clones.

     

EFFECTS OF MODERATE HEAT STRESS AND DISSOLVED INORGANIC CARBON CONCENTRATION ON PHOTOSYNTHESIS AND RESPIRATION OF SYMBIODINIUM SP. (DINOPHYCEAE) IN CULTURE AND IN SYMBIOSIS1

The influence of temperature and inorganic carbon (C_i) concentration on photosynthesis was examined in whole corals and samples of cultured symbiotic dinoflagellates (Symbiodinium sp.) using combined measurements from a membrane inlet mass spectrometer and chl a fluorometer. In whole corals, O₂ production at 26°C was significantly limited at C_i concentrations below ambient seawater (～2.2 mM). Further additions of C_i up to ～10 mM caused no further stimulation of oxygenic photosynthesis. Following exposure to 30°C (2 d), net oxygen production decreased significantly in whole corals, as a result of reduced production of photosynthetically derived oxygen rather than increased host consumption. Whole corals maintained a rate of oxygen evolution around eight times lower than cultured Symbiodinium sp. at inorganic carbon concentrations <2 mM, but cultures displayed greater levels of photoinhibition following heat treatment (30°C, 2 d). Whole corals and cultured zooxanthellae differed considerably in their responses to C_i concentration and moderate heat stress, demonstrating that cultured Symbiodinium make an incongruous model for those in hospite. Reduced net oxygen evolution, in whole corals, under conditions of low C_i (<2 mM) has been interpreted in terms of possible sink limitation leading to increased nonphotochemical energy dissipation. The advantages of combined measurement of net gas exchange and fluorometry offered by this method are discussed.     

Inhibitory effect of oxygen accumulation on the growth of Spirulina platensis

Summary The growth of Spirulina platensis was studied in a light-limited culture under various dissolved oxygen (DO) concentrations. At high DO concentration, e.g. at 1.25 mM DO, the growth rate was decreased up to 36 % compared with that of 0.063 mM DO. The retarded growth rate at high DO concentrations seemed to be coupled with the degeneration of photosynthetic activity in terms of O₂ evolution. Under higher DO concentrations, superoxide dismutase and ascorbate peroxidase activities tended to increase, while the contents of photosynthetic pigment, such phycocyanin, carotenoid and chlorophyll-a decreased distinctly.     

Ralstonia eutropha as a biocatalyst for desulfurization of dibenzothiophene

The potential of Ralstonia eutropha as a biocatalyst for desulfurization of dibenzothiophene (DBT) was studied in growing and resting cell conditions. The results of both conditions showed that sulfur was removed from DBT which accompanied by the formation of 2-hydroxybiphenyl (2-HBP). In growing cell experiments, glucose was used as an energy supplying substrate in initial concentrations of 55 mM (energy-limited) and 111 mM (energy-sufficient). The growing cell behaviors were quantitatively described using the logistic equation and maintenance concept. The results indicated that 2-HBP production was higher for the energy-sufficient cultures, while the values of the specific growth rate and the maintenance coefficient for these media were lower than those of the energy-limited cultures. Additionally, the kinetic studies showed that the half-saturation constant for the energy-limited cultures was 2 times higher than the energy-sufficient ones where the inhibition constant (0.08 mM) and the maximum specific DBT desulfurization rate (0.002 mmol g_cell ⁻¹ h⁻¹) were almost constant. By defining desulfurizing capacity (D _DBT) including both the biomass concentration and time to reach a particular percentage of DBT conversion, the best condition for desulfurizing cell was determined at 23% g_cell L⁻¹ h⁻¹ which corresponded with the resting cells that were harvested at the mid-exponential growth phase.

     

Mathematical modelling and kinetic study for CD production catalysed by Toruzyme® and CGTase from Bacillus firmus strain 37

A new mathematical model was developed for the kinetics of α-, β- and γ-cyclodextrin production, expanding an existing model that only included the production of β- and γ-cyclodextrins, because a detailed kinetic modelling of the reactions involved allows the manipulation of the process yields. The kinetic behaviour of the commercial enzyme Toruzyme^® was studied with maltodextrin as substrate at different concentrations and for CGTase from Bacillus firmus strain 37 at a concentration of 100 g L⁻¹. The mathematical model showed a proper fit to the experimental data, within the 24-h period studied, confirming that the considered hypotheses represent the kinetic behaviour of the enzymes in the reaction medium. The kinetic parameters generated by the model allowed reproducing previous observed qualitative tendencies as it can be seen that changing experimental conditions in the reaction process such as enzyme and substrate concentrations results in large changes in the enzyme kinetics and using high substrate concentrations does not guarantee the highest conversion rates due to enzyme inhibition and reverse reactions. In addition, this new mathematical model complements previous qualitative observations enabling the manipulation of the direct and reverse reactions catalysed by the enzyme by adjusting the reaction conditions, to target quantitative results of increased productivity and better efficiency in the production of a desired cyclodextrin.

     

Adaptation dynamics and evolutionary rescue under sulfide selection in cyanobacteria: a comparative study between Microcystis aeruginosa and Oscillatoria sp. (cyanobacteria)

Experimental evolution studies using cyanobacteria as model organisms are scarce despite the role of cyanobacteria in the evolution of photosynthesis. Three different experimental evolution approaches have been applied to shed light on the sulfide adaptation process, which played a key role in the evolution of this group. We used a Microcystis aeruginosa sulfide‐sensitive strain, unable to grow above ~0.1 mM, and an Oscillatoria sp. strain, isolated from a sulfureous spa (~0.2 mM total sulfide). First, performing a fluctuation analysis design using the spa waters as selective agent, we proved that M. aeruginosa was able to adapt to this sulfide level by rare spontaneous mutations. Second, applying a ratchet protocol, we tested if the limit of adaptation to sulfide of the two taxa was dependent on their initial sulfide tolerance, finding that M. aeruginosa adapted to 0.4 mM sulfide, and Oscillatoria sp. to ~2 mM sulfide, twice it highest tolerance level. Third, using an evolutionary rescue approach, we observed that both speed of exposure to increasing sulfide concentrations (deterioration rate) and populations’ genetic variation determined the survival of M. aeruginosa at lethal sulfide levels, with a higher dependence on genetic diversity. In conclusion, sulfide adaptation of sensitive cyanobacterial strains is possible by rare spontaneous mutations and the adaptation limits depend on the sulfide level present in strain’s original habitat. The high genetic diversity of a sulfide‐sensitive strain, even at fast environmental deterioration rates, could increase its possibility of survival even to a severe sulfide stress.     

Changes of leaf antioxidant system, photosynthesis and ultrastructure in tea plant under the stress of fluorine

Seedlings of Camellia sinensis were grown hydroponically for 30 d in order to study the effect of fluorine (F) on growth parameters, antioxidant defence system, photosynthesis and leaf ultrastructure. Fresh and dry mass, chlorophyll (Chl) content and net photosynthetic rate (P_N) decreased with increasing F concentration. Superoxide dismutase (SOD) activity decreased significantly, catalase (CAT) and guaiacol peroxidase (GPX) activities reached maximun under 0.21 and 0.32 mM F, respectively. Proline, malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents increased significantly. These results suggested, that antioxidant defence system of leaves did not sufficiently scavenge excessive reactive oxygen species. The cell ultrastructure was not changed under 0.11–0.21 mM F, however, it was destroyed at 0.32–0.53 mM F. So tea plants tolerated F in concentration less than 0.32 mM.     

Influence of oxygen concentration on the metabolism of Penicillium chrysogenum

In large-scale bioreactors, there is often insufficient mixing and as a consequence, cells experience uneven substrate and oxygen levels that influence product formation. In this study, the influence of dissolved oxygen (DO) gradients on the primary and secondary metabolism of a high producing industrial strain of Penicillium chrysogenum was investigated. Within a wide range of DO concentrations, obtained under chemostat conditions, we observed different responses from P. chrysogenum: (i) no influence on growth or penicillin production (>0.025 mmol L⁻¹); (ii) reduced penicillin production, but no growth limitation (0.013–0.025 mmol L⁻¹); and (iii) growth and penicillin production limitations (<0.013 mmol L⁻¹). In addition, scale down experiments were performed by oscillating the DO concentration in the bioreactor. We found that during DO oscillation, the penicillin production rate decreased below the value observed when a constant DO equal to the average oscillating DO value was used. To understand and predict the influence of oxygen levels on primary metabolism and penicillin production, we developed a black box model that was linked to a detailed kinetic model of the penicillin pathway. The model simulations represented the experimental data during the step experiments; however, during the oscillation experiments the predictions deviated, indicating the involvement of the central metabolism in penicillin production.     

Fumonisin B1-Induced Oxidative Burst Perturbed Photosynthetic Activity and Affected Antioxidant Enzymatic Response in Tomato Plants in Ethylene-Dependent Manner

Fumonisin B1 (FB1) is a harmful mycotoxin produced by Fusarium species, which results in oxidative stress leading to cell death in plants. FB1 perturbs the metabolism of sphingolipids and causes growth and yield reduction. This study was conducted to assess the role of ethylene in the production and metabolism of reactive oxygen species in the leaves of wild type (WT) and ethylene receptor mutant Never ripe (Nr) tomato and to elucidate the FB1-induced phytotoxic effects on the photosynthetic activity and antioxidant mechanisms triggered by FB1 stress. FB1 exposure resulted in significant ethylene emission in a concentration-dependent manner in both genotypes. Moreover, FB1 significantly affected the photosynthetic parameters of PSII and PSI and activated photoprotective mechanisms, such as non-photochemical quenching in both genotypes, especially under 10 µM FB1 concentration. Further, the net photosynthetic rate and stomatal conductance were significantly reduced in both genotypes in a FB1 dose-dependent manner. Interestingly, lipid peroxidation and loss of cell viability were also more pronounced in WT as compared to Nr leaves indicating the role of ethylene in cell death induction in the leaves. Thus, FB1-induced oxidative stress affected the working efficiency of PSI and PSII in both tomato genotypes. However, ethylene-dependent antioxidant enzymatic defense mechanisms were activated by FB1 and showed significantly elevated levels of superoxide dismutase (18.6%), ascorbate peroxidase (129.1%), and glutathione S-transferase activities (66.62%) in Nr mutants as compared to WT tomato plants confirming the role of ethylene in the regulation of cell death and defense mechanisms under the mycotoxin exposure.

     

Influence of temperature and nitrogen concentration on photosynthesis ofDunaliella viridis Teodoresco

The photosynthetic behaviour ofDunaliella viridis has been studied under a combination of three variables: irradiance (0–900 mol m^–2 s^–1), temperature (15, 23, 31, 38, 42 °C) and nitrogen concentration (0.05, 0.5, 1.5, 5, 10 mM NO ₃ ^- ) at a salinity of 2 M NaCl.The highest rates of photosynthesis have been found at 31 °C and a nitrate concentration of 10 mM. There exists a synergistic effect between temperature and nitrogen availability on the photosynthesis ofD. viridis; under nitrogen deficiency oxygen evolution is low, even null at high temperature. The interaction between these two variables of control occurs in a multiplicative way. There is also a general increase in photosynthetic pigments following the increase in nitrogen concentration in the culture medium. The normalization of net photosynthesis data in relation to chlorophylla shows that nitrogen concentration makes an indirect control of the photosynthetic rate ofD. viridis through the variation of pigment concentration.     

A kinetic model for the deactivation of pyruvate decarboxylase (PDC) by benzaldehyde

To provide further understanding of the biotransformation of benzaldehyde to L-phenylacetyl carbinol (L-PAC), an intermediate in L-ephedrine production, a kinetic model has been developed for the deactivation of pyruvate decarboxylase (PDC) by benzaldehyde. The model confirms that deactivation is first order with respect to benzaldehyde concentration and exhibits a square root dependency on time. The model covers the range of benzaldehyde concentrations 100–300 mM, as it has been shown previously that 200 mM benzaldehyde can produce L-PAC concentrations up to 190 mM (28.6 g/L) using partially purified PDC from Candida utilis.     

Substrates’ and products’ inhibition in fructanase production by a new Kluyveromyces marxianus CF15 from Agave tequilana fructan in a batch reactor

This study focuses on fructanase production in a batch reactor by a new strain isolated from agave juice (K. marxianus var. drosophilarum) employing different Agave tequilana fructan (ATF) concentrations as substrate. The experimental data suggest that the fructanase production may be inhibited or repressed by high substrate (50 g/L) and ethanol (20.7 g/L) concentrations present in culture medium. To further analyze these phenomena an unstructured kinetic mathematical model taking into account substrate and products inhibition was proposed and fitted. The mathematical model considers six reaction kinetics and the ethanol evaporation, and predicts satisfactorily the biomass, fructan, glucose, fructose, ethanol, and fructanase behavior for different raw material initial concentrations. The proposed model is the first to satisfactorily describe the production of fructanase from branched ATF with a new strain of K. marxianus.