Role of Reduced Exogenous Organic Compounds in the Physiology of the Blue-Green Bacteria (Algae): Photoheterotrophic Growth of a “Heterotrophic” Blue-Green Bacterium

Nostoc sp. (strain Mac) was shown to be capable of using glucose, fructose, or sucrose as a sole source of carbon and energy in the dark. In the light in the absence of exogenously supplied CO(2), this strain exhibited a more versatile metabolism. In addition to the three sugars above, glycerol and acetate served as sole sources of carbon. This photoheterotrophic growth in the absence of exogenously supplied CO(2) appears to involve O(2)-evolving photosynthesis. The action spectrum for photoheterotrophic growth on acetate closely resembles the action spectrum for photosynthesis. The physiology of photoheterotrophic growth was further investigated through determinations of stable carbon isotope ratios and measurements of gas exchanges. These investigations suggest that respired CO(2) from substrate oxidation is assimilated by the photosynthetic machinery.     

Bicarbonate Concentration by Synechocystis PCC6803 : Modulation of Protein Phosphorylation and Inorganic Carbon Transport by Glucose

The ability of the cyanobacterium Synechocystis PCC6803 to transport inorganic carbon in the form of bicarbonate rapidly decreased following a shift from bicarbonate-limited growth to either excess bicarbonate supply or to photoheterotrophic growth on glucose. Nonmetabolizable analogs of glucose did not exert this effect. The rate at which the bicarbonate uptake rate declined was too rapid to be accounted for by dilution of the activity by culture growth and suggested that posttranslational modification may be involved. Several proteins that were unphosphorylated during bicarbonate-limited growth became phosphorylated during the shifts to high CO₂ conditions and to photoheterotrophic growth. A similar alteration in the profile of phosphopolypeptides was observed following a shift into the dark. The changes in protein phosphorylation were not blocked by chloramphenicol or rifampicin.     

Regulating the ratio of photoautotrophic to heterotrophic metabolic activities in photoheterotrophic culture of Euglena gracilis and its application to α-tocopherol production

Methods of regulating the ratio of photoautotrophic to heterotrophic growth rates in photoheterotrophic culture of Euglena gracilis were investigated. In normal photoheterotrophic culture (in the presence of excess organic carbon), the cells grew mainly by organic carbon assimilation (heterotrophic metabolism). The relative contribution of photoautotrophic metabolism increased with the increase in the light supply coefficient, the increase in the CO₂ concentration in the aeration gas and the decrease in the feed rate of organic carbon source. However, limiting the organic carbon supply was the most effective method of shifting the metabolic balance to the photoautotrophic side. In the presence of excess organic carbon source, the -tocopherol contents of the cells in photoheterotrophic culture were low even when the light supply coefficient and CO₂ concentration in the aeration gas were high. By limiting the organic carbon supply to the photoheterotrophic culture, the intracellular content of -tocopherol increased to the same level as those obtained in photoautotrophic cultures.     

Effects of Gamma Stress and Carbon Dioxide on Eight Bioactive Flavonoids and Photosynthetic Efficiency in <Emphasis Type="Italic">Centella asiatica</Emphasis>

Increased atmospheric CO₂ and gamma irradiation have a significant impact on the plant photosynthetic apparatus and organic compound production. In this study, we evaluated the effect of elevated CO₂ on the photosynthetic efficiency and production of defensive secondary metabolites (flavonoids) induced by gamma irradiation as a physical elicitor in Centella asiatica. Irradiated and non-irradiated 10-week-old plants of C. asiatica were exposed to 400 and 800 μmol mol^?1 of atmospheric CO₂ in growth chambers for 2 h every day until six weeks. A CO₂-enriched atmosphere initially improved the photosynthetic efficiency and ameliorated the detrimental impact of gamma irradiation on the photosynthetic apparatus, increasing carbon allocation into the flavonoid pathway. Elevated CO₂ combined with gamma irradiation resulted in the highest concentration of flavonoids in C. asiatica tissues compared with the other treatments. There was an enhancement in rutin (2.49 fold), naringin (2.15 fold), fisetin (4.07 fold), and morin (4.62 fold) with rising CO₂ concentrations from 400 to 800 μmol mol^?1 in the irradiated plants. With increasing CO₂ concentration, the compensation point and the respiration declined, whereas the apparent quantum yield and the maximum net photosynthesis (A _max) rate increased. The efficiency of photosystem II (PSII) was improved in the irradiated plants grown under high concentrations of CO₂. The total carbohydrate concentration reached the maximum value at the highest level of CO₂, followed by gamma irradiation combined with the highest level of CO₂. Irradiated plants of C. asiatica grown under elevated CO₂ could be superior to non-irradiated plants due to increased carbon availability both for the flavonoid biosynthesis and for the photosynthetic pathway.     

Diel shifts in carboxylation pathway and metabolite dynamics in the CAM bromeliad Aechmea 'Maya' in response to elevated CO2

Background and Aims

The deployment of temporally separated carboxylation pathways for net CO₂ uptake in CAM plants provides plasticity and thus uncertainty on how species with this photosynthetic pathway will respond to life in a higher-CO₂ world. The present study examined how long-term exposure to elevated CO₂ influences the relative contributions that C₃ and C₄ carboxylation make to net carbon gain and to establish how this impacts on the availability of carbohydrates for export and growth and on water use efficiency over the day/night cycle.

Methods

Integrated measurements of leaf gas exchange and diel metabolite dynamics (e.g. malate, soluble sugars, starch) were made in leaves of the CAM bromeliad Aechmea ‘Maya’ after exposure to 700 µmol mol⁻¹ CO₂ for 5 months.

Key Results

There was a 60 % increase in 24-h carbon gain under elevated CO₂ due to a stimulation of daytime C₃ and C₄ carboxylation in phases II and IV where water use efficiency was comparable with that measured at night. The extra CO₂ taken up under elevated CO₂ was largely accumulated as hexose sugars during phase IV and net daytime export of carbohydrate was abolished. Under elevated CO₂ there was no stimulation of dark carboxylation and nocturnal export and respiration appeared to be the stronger sinks for carbohydrate.

Conclusions

Despite the increased size of the soluble sugar storage pool under elevated CO₂, there was no change in the net allocation of carbohydrates between provision of substrates for CAM and export/respiration in A. ‘Maya’. The data imply the existence of discrete pools of carbohydrate that provide substrate for CAM or sugars for export/respiration. The 2-fold increase in water-use efficiency could be a major physiological advantage to growth under elevated CO₂ in this CAM bromeliad.Key words: Aechmea ‘Maya’, carbon budgets, elevated CO₂, gas exchange, metabolite dynamics, PEPC, photosynthetic plasticity, Rubisco     

Purified crude glycerol by acid treatment allows to improve lipid productivity by Yarrowia lipolytica SKY7

In this study, crude glycerol with high potassium concentration was purified using acid treatment and used as carbon source for lipid production using Yarrowia lipolytica SKY7. The crude glycerol was purified using phosphoric acid (pH 2) followed by centrifugation. When purified glycerol was used as carbon source for fermentation, higher biomass productivity (0.54 g/L/h) and lipid productivity (0.2 g/L/h) was observed at 96 h compared to crude glycerol. Results indicated that 6.32 g/L potassium in crude glycerol medium was inhibitory for cell growth and lipid production by Y. lipolytica. Yield coefficients, productivities and specific growth rates were calculated for each glycerol medium. The process performance with purified glycerol medium was comparable to that of pure glycerol medium. A higher lipid yield was obtained in purified glycerol medium (0.21 g/g glycerol) than crude glycerol medium (0.124 g/g glycerol). During purification of crude glycerol, KH₂PO₄ was also produced as by-product. This study provides a way for valorization of crude glycerol with high potassium concentration for microbial lipid production.     

Carbon mass balance methodology to characterize the growth of pigmented marine bacteria under conditions of light cycling

A carbon mass balance methodology employing minimal measurements was applied to heterotrophic and photoheterotrophic marine bacteria grown under constant dilution and exposed to 12-h intervals of light or darkness. Carbon mass balance calculations using measurements taken every 3 h closed to within 93–103% using dissolved organic carbon, biomass carbon and CO₂ production data only, indicating that background interference from dissolved inorganic carbon variations in the amended seawater medium was not significant. Neither strain was observed to sustain a net CO₂ fixation using paramagnetic measurement of oxygen uptake rates (OUR), indicating a need for more sensitive on-line measurement techniques for OUR. Photoheterotrophic growth demonstrated lower carbon-mole biomass yields (0.41±0.026 vs. 0.64±0.013 mol mol^–1) despite higher specific glucose uptake rates (0.025 vs. 0.02 mol mol^–1 h^–1), suggesting that bioreactor-based study of marine bacteria can present growth modes that are different from those encountered in the marine environment.     

Role of Carbon Dioxide in Catabolism of Propane by “Nocardia paraffinicum” (Rhodococcus rhodochrous)

The catabolism of propane by “Nocardia paraffinicum” (Rhodococcus rhodochrous) has been shown to involve CO₂ fixation after its oxidation to propionic acid. “N. paraffinicum” failed to grow on either propane or 1-propanol in the absence of CO₂. The rate of propane utilization was directly related to the initial CO₂ concentration, and Warburg respirometry suggested that CO₂ was required for the catabolism of 1-propanol, propionaldehyde, and propionate but not for 2-propanol. These data also suggested that the predominant pathway for the utilization of propane by “N. paraffinicum” was through 1-propanol. The use of [2-¹⁴C]propane and ¹⁴CO₂ confirmed the catabolism of propane and the fixation of CO₂. Through the use of these isotopes and the pyruvate carboxylase inhibitor sodium arsenite, the labeled 2,4-dinitrophenylhydrazine derivative of pyruvate was trapped and isolated via thin-layer chromatography. The trapping of [¹⁴C]pyruvate in this manner was considered to be indicative of the presence of the methylmalonyl coenzyme A pathway for CO₂ fixation.     

Engineering a glycerol utilization pathway in Corynebacterium glutamicum for succinate production under O<Subscript>2</Subscript> deprivation

Objective

To explore the glycerol utilization pathway in Corynebacterium glutamicum for succinate production under O₂ deprivation.

Result

Overexpression of a glycerol facilitator, glycerol dehydrogenase and dihydroxyacetone kinase from Escherichia coli K-12 in C. glutamicum led to recombinant strains NC-3G diverting glycerol utilization towards succinate production under O₂ deprivation. Under these conditions, strain NC-3G efficiently consumed glycerol and produced succinate without growth. The recombinant C. glutamicum utilizing glycerol as the sole carbon source showed higher intracellular NADH/NAD⁺ ratio compare with utilizing glucose. The mass conversion of succinate increased from 0.64 to 0.95. Using an anaerobic fed-batch fermentation process, the final strain produced 38.4 g succinate/l with an average yield of 1.02 g/g.

Conclusions

The metabolically-engineered strains showed an efficient succinate production using glycerol as sole carbon source under O₂ deprivation.

     

The effect of atmospheric carbon dioxide concentrations on the performance of the mangrove Avicennia germinans over a range of salinities

By increasing water use efficiency and carbon assimilation, increasing atmospheric CO₂ concentrations could potentially improve plant productivity and growth at high salinities. To assess the effect of elevated CO₂ on the salinity response of a woody halophyte, we grew seedlings of the mangrove Avicennia germinans under a combination of five salinity treatments [from 5 to 65 parts per thousand (ppt)] and three CO₂ concentrations (280, 400 and 800 ppm). We measured survivorship, growth rate, photosynthetic gas exchange, root architecture and foliar nutrient and ion concentrations. The salinity optima for growth shifted higher with increasing concentrations of CO₂, from 0 ppt at 280 ppm to 35 ppt at 800 ppm. At optimal salinity conditions, carbon assimilation rates were significantly higher under elevated CO₂ concentrations. However, at salinities above the salinity optima, salinity had an expected negative effect on mangrove growth and carbon assimilation, which was not alleviated by elevated CO₂, despite a significant improvement in photosynthetic water use efficiency. This is likely due to non‐stomatal limitations to growth at high salinities, as indicated by our measurements of foliar ion concentrations that show a displacement of K⁺ by Na⁺ at elevated salinities that is not affected by CO₂. The observed shift in the optimal salinity for growth with increasing CO₂ concentrations changes the fundamental niche of this species and could have significant effects on future mangrove distribution patterns and interspecific interactions.     

Elevated Atmospheric CO<Subscript>2</Subscript> Increases Root Exudation of Carbon in Wetlands: Results from the First Free-Air CO<Subscript>2</Subscript> Enrichment Facility (FACE) in a Marshland

Experiments employing free-air CO₂ enrichment (FACE) facilities have indicated that elevated atmospheric carbon dioxide (eCO₂) stimulates growth in diverse terrestrial ecosystems. Studies of the effects of eCO₂ on wetland plants have indicated a similar response, but these studies were mostly performed in growth chambers. We conducted a 2-year FACE experiment [CO₂ ≈ 582 µmol mol^?1] in a marsh in Spain to test whether the common reed (Phragmites australis) responds to carbon enrichment, as previously reported in other macrophytes. More specifically, we tested the effect of eCO₂ on P. australis growth, photosynthesis, transpiration, and biomass, its effect on modifying plant and soil ratios of carbon, nitrogen, and phosphorus, and whether the strong environmental variability of this wetland modulates these responses. Our findings show that effects of eCO₂ in this wetland environment are more complex than previously believed, probably due to hydrological effects. The effects of eCO₂ on reed plants were cumulative and manifested at the end of the growing season as increased 38–44% instantaneous transpiration efficiency (ratio of net photosynthesis to transpiration), which was dependent on plant age. However, this increase did not result in a significant increase in biomass, because of excessive root exudation of carbon. These observations contrast with previous observations of wetland plants to increased atmospheric CO₂ in growth chambers and shed new light on the role of wetland plants as a carbon sink in the face of global climate change. The combined effects of water stress, eCO₂, and soil carbon processes must be considered when assessing the function of wetlands as a carbon sink under global change scenarios.     

Elevated CO2 improves root growth and cadmium accumulation in the hyperaccumulator Sedum alfredii

Aims

This study examined the effect of elevated CO₂ on plant growth, root morphology and Cd accumulation in S. alfredii, and assessed the possibility of using elevated CO₂ as fertilizer to enhance phytoremediation efficiency of Cd-contaminated soil by S. alfredii.

Methods

Both soil pot culture and hydroponic experiments were carried out to characterize plant biomass, root morphological parameters, and cadmium uptake in S. alfredii grown under ambient (350 μL L^?1) or elevated (800 μL L^?1) CO₂.

Results

Elevated CO₂ prompted the growth of S. alfredii, shoot and root biomass were increased by 24.6–36.7% and 35.0–52.1%, respectively, as compared with plants grown in ambient CO₂. After 10 days growth in medium containing 50 μM Cd under elevated CO₂, the development of lateral roots and root hairs were stimulated, additionally, root length, surface area, root volume and tip number were increased significantly, especially for the finest diameter roots. The total Cd uptake per pot was significantly greater under elevated CO₂ than under ambient CO₂. After 60 d growth, Cd phytoextraction efficiency was increased significantly in the elevated CO₂ treatment.

Conclusions

Results suggested that the use of elevated CO₂ may be a useful way to improve phytoremediation efficiency of Cd-contaminated soil by S. alfredii.     

Comparison analysis on the energy efficiencies and biomass yields in microbial CO2 fixation

CO₂ fixation by a hydrogen-oxidizing bacterium, Cupriavidus necator, was evaluated in a packed bed bioreactor under a constant flow rate of gas mixtures (H₂, O₂, CO₂). The overall energy efficiency depends on the efficiencies of CO₂ fixation into carbohydrate and the reduced carbon into biomass and bioproducts, respectively. The efficiencies varied with the limiting gas substrate. Under O₂ limitation, the efficiency (20–30%) of CO₂ fixation increased with time and was higher than the overall efficiency (12–18%). Under H₂ limitation, the efficiency of CO₂ fixation declined with time while the biomass yield was quite similar to that under O₂ limitation. A cellular metabolic model was suggested for the lithoautotrophic growth of C. necator, including CO₂ fixation into carbohydrate followed by the main metabolic pathway of reduced carbon. Under CO₂ limitation, most H₂ energy was wasted, resulting in a very low biomass yield. Under a dual limitation of O₂ and nitrogen, biosynthesis of poly(3-hydroxybutyrate) was triggered, and the energy efficiency or yield of biopolyester was lower than those of microbial cell mass. Compared with a green microalga Neochloris oleoabundans that produces lipid under nutrient limitation, C. necator exhibited a much higher (3–6 times) energy efficiency in producing biomass and bioproducts from CO₂.     

Use of sediment CO2 by submersed rooted plants

Background and Aims

Submersed plants have different strategies to overcome inorganic carbon limitation. It is generally assumed that only small rosette species (isoetids) are able to utilize the high sediment CO₂ availability. The present study examined to what extent five species of submersed freshwater plants with different morphology and growth characteristics (Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana and Hydrocotyle verticillata) are able to support photosynthesis supplied by uptake of CO₂ from the sediment.

Methods

Gross photosynthesis was measured in two-compartment split chambers with low inorganic carbon availability in leaf compartments and variable CO₂ availability (0 to >8 mmol L⁻¹) in root compartments. Photosynthetic rates based on root-supplied CO₂ were compared with maximum rates obtained at saturating leaf CO₂ availability, and ¹⁴C experiments were conducted for two species to localize bottlenecks for utilization of sediment CO₂.

Key Results

All species except Hydrocotyle were able to use sediment CO₂, however, with variable efficiency, and with the isoetid, Lobelia, as clearly the most effective and the elodeid, Ludwigia, as the least efficient. At a water column CO₂ concentration in equilibrium with air, Lobelia, Lilaeopsis and Vallisneria covered >75% of their CO₂ requirements by sediment uptake, and sediment CO₂ contributed substantially to photosynthesis at water CO₂ concentrations up to 1000 µmol L⁻¹. For all species except Ludwigia, the shoot to root ratio on an areal basis was the single factor best explaining variability in the importance of sediment CO₂. For Ludwigia, diffusion barriers limited uptake or transport from roots to stems and transport from stems to leaves.

Conclusions

Submersed plants other than isoetids can utilize sediment CO₂, and small and medium sized elodeids with high root to shoot area in particular may benefit substantially from uptake of sediment CO₂ in low alkaline lakes.Key words: Submersed rooted plants, CO₂ uptake, sediment CO₂, Lobelia dortmanna, Lilaeopsis macloviana, Ludwigia repens, Vallisneria americana, Hydrocotyle verticillata     

Preference of carbon absorption determines the competitive ability of algae along atmospheric CO2 concentration

Although many studies have focused on the effects of elevated atmospheric CO₂ on algal growth, few of them have demonstrated how CO₂ interacts with carbon absorption capacity to determine the algal competition at the population level. We conducted a pairwise competition experiment of Phormidium sp., Scenedesmus quadricauda, Chlorella vulgaris and Synedra ulna. The results showed that when the CO₂ concentration increased from 400 to 760 ppm, the competitiveness of S. quadricauda increased, the competitiveness of Phormidium sp. and C. vulgaris decreased, and the competitiveness of S. ulna was always the lowest. We constructed a model to explore whether interspecific differences in affinity and flux rate for CO₂ and HCO₃ ⁻ could explain changes in competitiveness between algae species along the gradient of atmospheric CO₂ concentration. Affinity and flux rates are the capture capacity and transport capacity of substrate respectively, and are inversely proportional to each other. The simulation results showed that, when the atmospheric CO₂ concentration was low, species with high affinity for both CO₂ and HCO₃ ⁻ (HCHH) had the highest competitiveness, followed by the species with high affinity for CO₂ and low affinity for HCO₃ ⁻ (HCLH), the species with low affinity for CO₂ and high affinity for HCO₃ ⁻ (LCHH) and the species with low affinity for both CO₂ and HCO₃ ⁻ (LCLH); when the CO₂ concentration was high, the species were ranked according to the competitive ability: LCHH > LCLH > HCHH > HCLH. Thus, low resource concentration is beneficial to the growth and reproduction of algae with high affinity. With the increase in atmospheric CO₂ concentration, the competitive advantage changed from HCHH species to LCHH species. These results indicate the important species types contributing to water bloom under the background of increasing global atmospheric CO₂, highlighting the importance of carbon absorption characteristics in understanding, predicting and regulating population dynamics and community composition of algae.     

Enhanced autotrophic growth of <Emphasis Type="Italic">Nannochloris</Emphasis> sp. with trona buffer for sustainable carbon recycle

In this study, a potential applicability of a modified Shuisheng-4 culture medium with trona buffer for CO₂(g) capture and the resultant CO₂-rich solution was investigated for the autotrophic growth of Nannochloris sp. Trona is an inexpensive naturally-occurring mineral with high solubility in water. Trona solution after absorbing CO₂(g) controlled at pH ~7 ~ 8 contains high dissolved inorganic carbon (DIC) concentration in water applicable to both open and closed systems and the pH is suitable for the growth. High DIC concentration was also found to enhance the autotrophic growth rate when the Na⁺ concentration is ~ < 0.12 M. However, the tolerance of a marine green alga, Nannochloris sp., to Na⁺ ion was found to twice as much as that of a freshwater green alga, Chlorella vulgaris. Therefore, it is anticipated that trona buffer solution has potential for better CO₂ utilization for the mutual benefit of microalgae-derived biofuels production and carbon recycle.     

Regulation of carbon metabolic fluxes in response to CO<Subscript>2</Subscript> supplementation in phototrophic <Emphasis Type="Italic">Chlorella vulgaris</Emphasis>: a cytomic and biochemical study

As one of the promising species of microalgae for biofuel production, Chlorella vulgaris CS-42 was cultivated phototrophically in two cylindrical photobioreactors with aeration of 5 % (v/v) CO₂ or air for 13 days to evaluate the effects of CO₂ supplementation on biomass, CO₂ fixation performance, and biochemical content. Significant increases of specific growth rate and total carbon content in biomass resulting in a higher CO₂ fixation rate were found with 5 % CO₂. The maximum biomass concentration, carbohydrate and fatty acid contents with 5 % CO₂ were significantly higher than those with air, while carbohydrate biosynthesis was most affected as compared to other biochemical components. Cytomic analysis revealed a rapid accumulation of neutral lipid in the late growth phase with more lipid bodies visualized by confocal laser scanning microscopy (CLSM), when nitrate consumption was accelerated with CO₂ supplementation. Gas chromatography mass spectrometry (GC-MS) analysis indicated that 5 % CO₂ favored the formation of C18:2, which led to a decrease in the degree of lipid unsaturation (DLU). These results proved that CO₂ supplementation was one of the most efficient methods to significantly prompt the growth of microalgae and increase the C/N ratio in the medium, which in turn regulated the carbon metabolic flux to enhance neutral lipid and fatty acid production in C. vulgaris.