Carbohydrate Production Research Articles

Synergy of production of value-added bioplastic, astaxanthin and phycobilin co-products and Direct Green 6 textile dye remediation in Spirulina platensis

Phyco-remediation of dyestuffs in textile wastewaters is of economic, industrial, and environmental importance. We evaluated the remediation of the textile dye, Direct Green 6 (DG6), by Spirulina platensis, and investigated the novel possibility that DG6 treatment enhances production of the biopolymer, polyhydroxybutyrate (PHB). We showed that both live and dead cells of Spirulina were capable of DG6 remediation, but live cells could be re-used with no loss of remediation efficiency. Furthermore, DG6 remediation by live cells resulted in increased algal biomass and trichome lengths, and stimulated production of valuable metabolites, including PHB, antioxidants, carbohydrates and pigments (phycobilins and astaxanthin). We determined the optimal conditions for DG6 remediation and an artificial neural network (ANN) accurately modeled the experimental data and predicted the concentration of dye as the most and algal turbidity as the least important parameters for DG6 removal efficiency. A DG6 concentration of 60 mg L−1 resulted in the highest simultaneous co-production of PHB (12.7 ± 1.7% DW) and increase of astaxanthin (194%), carotenoids (50%), phenol (51%), carbohydrates (27%) total phycobilin (43%), together with the enhancement of biomass and trichome lengths (95%). Oxidative stress indices and enzyme activities such as peroxidases and laccase (involved in dye removal/antioxidant functions) were also increased by dye dosage. On the basis of our results, we propose that S. platensis may use DG6 dye as a nitrogen/carbon source for co-accumulation of valuable bioplastic and metabolites.

Could co-substrate sodium acetate simultaneously promote Chlorella to degrade amoxicillin and produce bioresources?

Integrating microalgae culture and wastewater purification is a promising technology for sustainable bioresource production. However, the challenge is that toxins in wastewater usually limit risk elimination and cause poor bioresource production. Easy-to-biodegrade substrates could alleviate the resistant stress on a bacterial community but we know little about how they function with microalgae. In this study, we tested if Easy-to-biodegrade substrates could simultaneously promote Chlorella to degrade antibiotic amoxicillin (AMO) and produce bioresources. Sodium acetate (NaAC) was used as the representative co-substrate. The results showed NaAC could enhance AMO removal by 76%. The β-lactam structure was destroyed and detoxified to small molecules, due to the up-regulation of hydrolase, oxidoreductase, reductase, and transferase. Chlorella biomass production increased by 36%. The genes encoding the glutathione metabolism and peroxisome pathways were significantly up-regulated to alleviate the antibiotic stress, and the DNA replication pathway was activated. As a result, the production of lipid, carbohydrate, and protein was enhanced by 61%, 122%, and 34%, respectively. This study provides new insights for using microalgae to recover bioresources from toxic wastewater and reveals the critical underlying mechanisms.

Optimization of microwave-assisted carbohydrate extraction from indigenous Scenedesmus sp. grown in brewery effluent using response surface methodology

The use of wastewater as a nutrient source for microalgae cultivation is considered as a cost-effective approach for algal biomass and biofuel production. The microalgal biomass contains carbohydrates that can be processed into bioethanol through different extraction methods. The objective of this study is to optimize the microwave-assisted extraction (MAE) of carbohydrates from the indigenous Scenedesmus sp. grown on brewery effluent. Optimization of independent variables, such as acid concentration (0.1–5 N), microwave power (800–1200 W), temperature (80–180 °C) and extraction time (5–30 min) performed by response surface methodology. It was found that all independent variables had a significant and positive effect on microwave-assisted carbohydrate extraction. The quadratic model developed on the basis of carbohydrate yield had F value of 112.05 with P < 0.05, indicating that the model was significant to predict the carbohydrate yield. The model had a high value of R2 (0.9899) and adjusted R2 (0.9811), indicating that the fitted model displayed a good agreement between the predicted and actual carbohydrate yield. An optimum carbohydrate yield obtained was 260.54 mg g−1 under the optimum conditions of acid concentration (2.8 N), microwave power (1075 W), temperature (151 °C) and extraction time (22 min). The validation test showed that the model has adequately described the microwave-assisted extraction (MAE) of carbohydrates from microalgal biomass. This study demonstrated that the indigenous Scenedesmus sp. grown on brewery effluent provides a promising result in carbohydrate production for bioethanol feedstock.

Chlorella minutissima grown with xylose and arabinose in tubular photobioreactors: Evaluation of kinetics, carbohydrate production, and protein profile

Lignocellulosic waste is the most abundant global renewable biomass source and contains significant amounts of pentoses. Thus, pentoses can be considered potential carbon sources for the culture media for microalgae cultivation. The present study aimed to determine whether the addition of D-xylose and L-arabinose and lighting variations influence the carbohydrate and protein profiles of Chlorella minutissima grown in tubular photobioreactors. The highest biomass concentration of 1.55 g L−1 was attained by the control cultures exposed to a light intensity of 40.50 μmol m−2 s−1. The highest carbohydrate accumulation (66.4%) was obtained through the combined use of 40.50 μmol m−2 s−1 light intensity, 19.16 mg L−1 D-xylose, 0.89 mg L−1 L-arabinose, and 0.125 g L−1 KNO3. A reduction in luminosity and the addition of pentoses altered the protein profile of Chlorella minutissima. Thus, growth and carbohydrate production can be stimulated by pentoses and adequate luminous intensity. Therefore, Chlorella minutissima can be considered a potential source of biomass for bioethanol production.

Erratum to: The effects of phosphate on physiological responses and carbohydrate production in Ulva fasciata (Chlorophyta) from upwelling and non-upwelling site

Erratum to: The effects of phosphate on physiological responses and carbohydrate production in <i>Ulva fasciata</i> (Chlorophyta) from upwelling and non-upwelling site

Multi-Wall Carbon Nanotubes Promote the Growth of Maize (Zea mays) by Regulating Carbon and Nitrogen Metabolism in Leaves.

Previous studies have suggested that multiwalled carbon nanotubes (MWCNTs) promote plant growth; however, the mechanism is yet to be fully understood. In this study, the effects of MWCNTs (20, 100, and 500 mg/L) on the carbon (C) and nitrogen (N) metabolism in maize were studied to explore the molecular mechanism of the action of MWCNTs on plants. The results showed that 100 mg/L MWCNTs increased the shoot fresh and dry weight, root fresh weight, and seedling length while other doses showed no significant effects. Further studies showed that 100 mg/L MWCNTs increased the chlorophyll content, transpiration rate, stomatal conductance, and intercellular CO2 concentration, by 50.6%, 60.8%, 47.2%, and 32.1%, respectively. Activities of key enzymes including sucrose synthase (SS), sucrose phosphate synthase (SPS) and phosphoenolpyruvate carboxylase (PEPC) that are involved in the carbon metabolism, and nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthetase (GOGAT) that are involved in N metabolism, were all upregulated by 100 mg/L MWCNTs, which contributed to the increase of the accumulation of carbohydrates (sugar and starch), soluble protein, and N in plants. These findings suggest that MWCNTs can improve plant growth by regulating the key enzymes involved in C and N metabolism thereby enhancing the carbohydrate production and the use of N and improving plant growth. This study provides significant insights into the molecular mechanism of the positive effects of MWCNTs on plants and provide a basis for the agricultural application of MWCNTs.

Formation of Proto-Kranz in C3 Rice Induced by Spike-Stalk Injection Method.

Introduction of C4 photosynthetic traits into C3 crops is an important strategy for improving photosynthetic capacity and productivity. Here, we report the research results of a variant line of sorghum–rice (SR) plant with big panicle and high spikelet density by introducing sorghum genome DNA into rice by spike-stalk injection. The whole-genome resequencing showed that a few sorghum genes could be integrated into the rice genome. Gene expression was confirmed for two C4 photosynthetic enzymes containing pyruvate, orthophosphate dikinase and phosphoenolpyruvate carboxykinase. Exogenous sorghum DNA integration induced a series of key traits associated with the C4 pathway called “proto-Kranz” anatomy, including leaf thickness, bundle sheath number and size, and chloroplast size in bundle sheath cells. Significantly, transgenic plants exhibited enhanced photosynthetic capacity resulting from both photosynthetic CO2-concentrating effect and improved energy balance, which led to an increase in carbohydrate levels and productivity. Furthermore, such rice plant exhibited delayed leaf senescence. In summary, this study provides a proof for the feasibility of inducing the transition from C3 leaf anatomy to proto-Kranz by spike-stalk injection to achieve efficient photosynthesis and increase productivity.

Microalgae cultivation using nutrients in fish farm effluent for biodiesel production

This article contributes to research on the composition of microalgae grown in fish farm wastewater (FFW), particularly for use in biodiesel production. In this research, Tetradesmus obliquus, Heterochlorella luteoviridis, and Chlamydomonas reinhardtii, cultivated in unmodified-and modified FFW, and the standard growth media, Tris-Acetate-Phosphate (TAP), were studied. The following parameters of the algae species were investigated: specific growth rate, biomass yield, biomass productivity, lipid content and carbohydrate content. Additionally, lipids and carbohydrate productivities were calculated, and the rate of CO2 uptake was determined. This study showed that the nutrients in FFW were suitable for algae biomass cultivation for biodiesel production. Chlamydomonas reinhardtii, in unmodified FFW, had the highest lipid and carbohydrate composition of 44.08% and 35.04%, respectively, and was most suited for biodiesel production as well as nutrient removal. The modified FFW only had the extra benefit of near-complete nutrient removal, but a comparable yield and biochemical composition with samples in unmodified FFW. A similar effect of CO2 concentration was observed in both the unmodified and modified FFW.

The Lichens' Microbiota, Still a Mystery?

Lichens represent self-supporting symbioses, which occur in a wide range of terrestrial habitats and which contribute significantly to mineral cycling and energy flow at a global scale. Lichens usually grow much slower than higher plants. Nevertheless, lichens can contribute substantially to biomass production. This review focuses on the lichen symbiosis in general and especially on the model species Lobaria pulmonaria L. Hoffm., which is a large foliose lichen that occurs worldwide on tree trunks in undisturbed forests with long ecological continuity. In comparison to many other lichens, L. pulmonaria is less tolerant to desiccation and highly sensitive to air pollution. The name-giving mycobiont (belonging to the Ascomycota), provides a protective layer covering a layer of the green-algal photobiont (Dictyochloropsis reticulata) and interspersed cyanobacterial cell clusters (Nostoc spec.). Recently performed metaproteome analyses confirm the partition of functions in lichen partnerships. The ample functional diversity of the mycobiont contrasts the predominant function of the photobiont in production (and secretion) of energy-rich carbohydrates, and the cyanobiont’s contribution by nitrogen fixation. In addition, high throughput and state-of-the-art metagenomics and community fingerprinting, metatranscriptomics, and MS-based metaproteomics identify the bacterial community present on L. pulmonaria as a surprisingly abundant and structurally integrated element of the lichen symbiosis. Comparative metaproteome analyses of lichens from different sampling sites suggest the presence of a relatively stable core microbiome and a sampling site-specific portion of the microbiome. Moreover, these studies indicate how the microbiota may contribute to the symbiotic system, to improve its health, growth and fitness.

Evaluation of passiflora edulis flavicarpa and dioscorea spp. peelings as potential raw material for biorefineries

The use of agro-industrial residues in biorefinery processes has been increasing due to the negative environmental impact associated with the excessive use of fossil fuels. Several residues have been evaluated as precursors for carbohydrate production, which in turn can be converted into numerous high value-added products, such as the products of the furanic series, 5-hydroxymethylfurfural and furfural. Thus, this work aimed to determine the chemical composition of passion fruit and purple yam peels in order to analyze their potential for use as raw material for biorefineries. For the determination of sugars, the shells were submitted to acid hydrolysis according to two different methodologies: one by the National Renewable Energy Laboratory method and the other by the Dunning et al. (1949) methodology. The products obtained were analyzed by Fourier Transform Infrared Spectrophotometry and High-Performance Liquid Chromatography. The results show that passion fruit and purple yam peels presented high percentages of hemicellulose (30% and 15%, respectively) and mainly of cellulose (above 44% for both shells according to the two tested methodologies). Due to the significant amount of these polysaccharides present in the biomass, they have potential for use in biorefineries.

A strategy for lipid production in Scenedesmus sp. by multiple stresses induction

Microalgae are rich source of lipids and are one of the promising feedstocks for biofuel production, whereas enhancement of lipid, carbohydrate, and biomass production is crucial for commercialization of algal biofuels. Nutrients/salinity stresses are important to increase the synthesis of lipid. In the present study, Scenedesmus sp. is treated with a varying combination of sodium nitrate (NaNO3), dipotassium hydrogen phosphate (K2HPO4), and sodium chloride (NaCl) to improve lipid accumulation. Results indicate that the modified media comprising of NaCl (100 mM), NaNO3 (0 mM), and K2HPO4 (0.22 mM) (S100N0P0.22) accumulated higher quantities of lipid (385.4 ± 34.2 μg/mg) along with considerable biomass (537.0 ± 22.3 μg/mL), chlorophyll “a” (6.2 ± 0.08 μg/mL), and palmitic acid (32.6%). Apart from biochemical analysis, stress-induced biomarker such as hydrogen peroxide (H2O2) was observed maximum for same combination (10854 μmolH2O2/g), with low lipid peroxidation (3.2 μmol/g). Catalase (CAT) and superoxide dismutase (SOD) activity were further studied to monitor the impact of reactive oxygen species (ROS) on lipid accumulation. This study revealed a better combination in terms of lipid and biomass profile, which can further be investigated for large-scale production. Multi-stress-driven lipid production is one of the significant outputs of the current study, which can further be explored in detail. Insight such interactions may provide directions for economical production of algal biodiesel.

Comparison between the toxicity of Copper and Irgarol 1051 as two different generations of antifoulings on growth and essential metabolites of marine algae (Dunaliella salina as a case study)

The present study aims to compare the toxicity effect of Copper and Irgarol 1051 as antifouling agents on metabolites products in marine algae Dunaliella salina. Different concentrations of Cu (5, 15 & 25 mg/l) and Irgarol 1051 (0.012, 0.025 & 0.050 μg/l) were laboratories prepared and their impacts on growth, protein, and carbohydrates in Dunaliella salina were tested. Selections of these concentrations were initiated based on the response of the studied alga which had slightly or marked effects on its growth, and also to avoid the non-effective and directly lethal concentrations on the experimented alga. The obtained results showed stimulation in the growth of algae under the effect of the lowest concentration of the two tested antifoulings, however, there was a suppression of algal growth by increasing the concentration of the two antifoulings but with different degrees. There was a clear inhibition of protein and carbohydrate production by increasing the concentration of the two tested antifoulings. Also, Irgarol 1051 showed a toxic effect higher than Copper which is one of the essential micronutrients in the marine ecosystem.

Enhanced Arthrospira platensis Biomass Production Combined with Anaerobic Cattle Wastewater Bioremediation.

Microalgae biomasses offer important benefits regarding macromolecules that serve as promising raw materials for sustainable production. In the present study, the microalgae Arthrospira platensis DHR 20 was cultivated in horizontal photobioreactors (HPBR), with and without temperature control, in batch mode (6 to 7 days), with anaerobically digested cattle wastewater (ACWW) as substrate. High dry biomass concentrations were observed (6.3–7.15 g L−1). Volumetric protein, carbohydrate, and lipid productivities were 0.299, 0.135, and 0.108 g L−1 day−1, respectively. Promising lipid productivities per area were estimated between 22.257 and 39.446 L ha−1 year−1. High CO2 bio-fixation rates were recorded (875.6–1051 mg L−1 day−1), indicating the relevant potential of the studied microalgae to mitigate atmospheric pollution. Carbon concentrations in biomass ranged between 41.8 and 43.6%. ACWW bioremediation was satisfactory, with BOD5 and COD removal efficiencies of 72.2–82.6% and 63.3–73.6%. Maximum values of 100, 95.5, 92.4, 80, 98, and 94% were achieved concerning the removal of NH4+, NO3−, Pt, SO42−, Zn, and Cu, respectively. Total and thermotolerant coliform removals reached 99–99.7% and 99.7–99.9%. This microalgae-mediated process is, thus, promising for ACWW bioremediation and valuation, producing a microalgae biomass rich in macromolecules that can be used to obtain friendly bio-based products and bioenergy.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12155-021-10258-4.

Nitrogen availability affects stem development and response to differential root-zone drought stress in Catalpa bungei

A greenhouse experiment was conducted to explore how nitrogen availability affects drought responses and stem development of Catalpa bungei seedlings under partial root-zone drought. A factorial design consisting of two N rates [adequate-N (AN) and low-N (LN)] and four water treatments [well-watered (WW), horizontally partial root-zone drought (H-PRD), vertically partial root-zone drought (V-PRD) and full root-zone drought (FRD)] was used. On the whole, the effects of nitrogen applications on seedling growth, physiological parameters and gene expression of key genes may vary among different water treatments. For example, A, E, gs and CO2int were significantly increased under WW and V-PRD conditions while A and WUEi were decreased under FRD by N addition. As compared with the sharp stoma closure under FRD, stoma was moderately regulated under H-PRD and V-PRD conditions by triggering a network of signaling including phytohormones, NO and Ca2+. Despite the more sensitive drought responses under H-PRD, the intrinsic water use efficiency (WUEi) was higher under V-PRD, mainly due to the homeostasis of abscisic acid (ABA) signals. The higher WUEi and the efficient carbohydrate production contributed to the dominant xylem development under V-PRD. In contrast, the constitutive activation of ABA signaling over long-term H-PRD reduced WUEi and thus suppressed stem growth under H-PRD. The dominant WUEi under V-PRD condition contributed to the positive effect of N addition on xylem development. Moreover, N application increased IAA levels and the transcription of critical PIPs genes, which contributed to the dominant WUEi and xylem development under V-PRD conditions.

Producing Energy-Rich Microalgae Biomass for Liquid Biofuels: Influence of Strain Selection and Culture Conditions

Energy-storage metabolites such as neutral lipids and carbohydrates are valuable compounds for liquid biofuel production. The aim of this work is to elucidate the main biological responses of two algae species known for their effective energy-rich compound accumulation in nitrogen limitation and day–night cycles: Nannochloropsis gaditana, a seawater species, and Parachlorella kessleri, a freshwater species. Lipid and carbohydrate production are investigated, as well as cell resistance to mechanical disruption for energy-rich compound release. Nitrogen-depleted N. gaditana showed only a low consumption of energy-storage molecules with a non-significant preference for neutral lipids (TAG) and carbohydrates in day–night cycles. However, it did accumulate significantly fewer carbohydrates than P. kessleri. Following this, the highest levels of productivity for N. gaditana in chemostat cultures at four levels of nitrogen limitation were found to be 3.4 and 2.2 × 10−3 kg/m2·d for carbohydrates and TAG, respectively, at 56%NO3 limitation. The cell disruption rate of N. gaditana decreased along with nitrogen limitation, from 75% (at 200%NO3) to 17% (at 13%NO3). In the context of potentially recoverable energy for biofuels, P. kessleri showed good potential for biodiesel and high potential for bioethanol; by contrast, N. gaditana was found to be more efficient for biodiesel production only.

Production of β-glucan exopolysaccharide lasiodiplodan by Lasiodiplodia theobromae CCT 3966 from corn bran acid hydrolysate.

The potential utilization of corn bran acid hydrolysate (CBAH) was evaluated as an inexpensive feedstock for the production of a rich carbohydrate and protein medium for lasiodiplodan (LAS) production using the filamentous fungus Lasiodiplodia theobromae CCT 3966. Experiments were performed according to a 22 CCRD experimental design aiming to evaluate the influence of agitation speed (rpm) and temperature (°C) over the production of total cell biomass (TCB) and LAS concentration released to the medium (LAS-M), adhered to biomass (LAS-C), and total (LAS-T). Under the selected conditions (temperature of 28°C and agitation of 200 rpm), 8.73 g·L-1 of LAS-T and 4.47 g·L-1 of TCB were obtained. Recovery of LAS-C with hot water was shown as an alternative to increase the production concentration, although it might require further purification steps. CBAH potential for substitution of synthetic media was demonstrated, indicating that it is an adequate raw material containing all necessary nutrients for LAS production.Key points• Corn bran acid hydrolysate is presented as a suitable substrate for β-glucan production.• Lasiodiplodia theobromae CCT 3966 have the potential for the industrial β-glucan production.• Simple recovering of biomass-adhered lasiodiplodan by hot water extraction.

The redistribution and migration mechanism of nitrogen in the hydrothermal co‑carbonization process of sewage sludge and lignocellulosic wastes

Blending lignocellulosic wastes (such as cornstalk, CS) into sewage sludge (SS) for hydrothermal carbonization (HTC) could contribute to the importance of the hydrothermal solid product (hydrochar) as a substitute for fossil fuel. However, the interactions between SS and CS changed the fate of Nitrogen (N), affecting the clean combustion utilization of hydrochar. This study focused on the influence of SS–CS interactions on the redistribution and migration behavior of N during the co-HTC process by tuning the mass ratio of SS to CS (SS:CS), reaction temperature, and residence time. Under the hydrothermal condition of 220 °C, 2 h, and SS:CS = 1:1, the high heating value of hydrochar and the energy recovery efficiency (ERE) respectively reached 15.89 MJ/kg and 71.19%. Further raising the temperature to 250 °C, the hydrochar was enhanced in the coalification degree, whereas ERE decreased to 61.86%. Part of the amino-N in sludge organics was fractured during the co-HTC process and reacted with carbohydrate and intermediate products, such as 5-hydroxymethylfurfural, which degraded from CS, to generate heterocyclic-N compounds (including pyridine, pyrrole, and pyrazine). The remaining amino-N formed pyridine-N, pyrrole-N, and quaternary-N through various solid–solid conversions. The heterocyclic-N polymerized and formed melanoidins, which thereafter polymerized with aromatic clusters to form the N-containing polyaromatic char. Therefore, the N retention rate (NRR) was enhanced and showed a synergistic effect. NRR was increased by raising the proportion of CS or extending time, reaching 57.02% at SS:CS = 1:1 and 8 h. Conversely, rising temperatures resulted in a downward trend of NRR with a phased increase at 220 °C–250 °C.

Thermal decomposition of biomass wastes derived from palm oil production

The palm oil industry produces large amounts of biomass by-products, such as palm empty fruit bunch (EFB), mesocarp fiber (MF), and kernel shell (KS). The thermal behavior and decomposition of the oil palm biomass wastes have been studied by thermogravimetry/mass spectrometry (TG/MS) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The determination of biopolymer and inorganic composition facilitated the interpretation of the thermal decomposition results. It was established that the chemical compositions of KS and MF were similar, while EFB contained significantly higher amount of cellulose and potassium, and decomposed in a narrower temperature range. In addition to the thermogravimetric curves (TG and DTG), the product distribution of pyrolyzates also reflected the compositional differences. Py-GC/MS and TG/MS experiments showed that the increasing potassium content of the samples reduced the intensity of 4-hydroxy-5,6-dihydro-2H-pyran-2-one, which is formed via depolymerization and dehydration of xylan units. Consequently, these experiments proved that beside cellulose, the depolymerization of hemicellulose was also hindered, while the dehydration, fragmentation, and charring reactions were catalyzed by potassium. Additionally, the evolution of the characteristic cellulose and lignin products shifted to lower temperatures. The most dominant aromatic pyrolysis product was phenol from each sample, which formed to a large extent from the abundant 4-hydroxybenzoate (4Hb) lignin subunits by scission and decarboxylation. KS also produced 4-hydroxybenzoic acid in significant amounts during pyrolysis at 450 °C confirming the presence of 4Hb subunits in lignin. The evolution of phenol started at 220 °C from the 4Hb moieties, and ended at about 600 °C from the residual phenolic units, while the release of guaiacol, vinylguaiacol, and syringol occurred between 300 and 450 °C as monitored by TG/MS. Some characteristic carbohydrate products were attributed to either hemicellulose or cellulose degradation based on the evolution profiles of KS and MF with separated carbohydrate decomposition steps. The comparison of the oil palm biomass wastes showed that EFB is supposed to be treated separately from KS and MF during the utilization process due to the different thermal behavior and composition.

Single-phase and two-phase cultivations using different light regimes to improve production of valuable substances in the anoxygenic photosynthetic bacterium Rhodopseudomonas faecalis PA2

This study aimed to improve biomass, carotenoid, bacteriochlorophyll, protein, lipid, and carbohydrate contents of Rhodopseudomonas faecalis PA2 using different light regimes. Light intensity (4000, 6000, 8000, and 10,000 lx), together with photoperiod (24:0, 16:8, 12:12, and 8:16 h light/dark), was assigned as single-phase (SP) cultivation while two-phase (TP) cultivation used two light intensities (using 4000 lx as the first phase), together with the control of phase shift (3, 6, and 9 days) and photoperiod. Biomass, carotenoid, and bacteriochlorophyll contents were maximized by SP cultivation; light at 8000 lx with light-dark cycle of 24:0 was optimal for pigments synthesis. In contrast, TP was useful to enhance storage compounds; protein, lipid, and carbohydrate productivities were significantly increased by 121.69%, 101.69%, and 92.44%, respectively, in TP when compared with SP. This indicates that the novel light strategy proposed in this study was able to manipulate the production of valuable substances in this strain.

The metabolic origins of non-photorespiratory CO2 release during photosynthesis: a metabolic flux analysis.

Respiration in the light (RL) releases CO2 in photosynthesizing leaves and is a phenomenon that occurs independently from photorespiration. Since RL lowers net carbon fixation, understanding RL could help improve plant carbon-use efficiency and models of crop photosynthesis. Although RL was identified more than 75 years ago, its biochemical mechanisms remain unclear. To identify reactions contributing to RL, we mapped metabolic fluxes in photosynthesizing source leaves of the oilseed crop and model plant camelina (Camelina sativa). We performed a flux analysis using isotopic labeling patterns of central metabolites during 13CO2 labeling time course, gas exchange, and carbohydrate production rate experiments. To quantify the contributions of multiple potential CO2 sources with statistical and biological confidence, we increased the number of metabolites measured and reduced biological and technical heterogeneity by using single mature source leaves and quickly quenching metabolism by directly injecting liquid N2; we then compared the goodness-of-fit between these data and data from models with alternative metabolic network structures and constraints. Our analysis predicted that RL releases 5.2 μmol CO2 g-1 FW h-1 of CO2, which is relatively consistent with a value of 9.3 μmol CO2 g-1 FW h-1 measured by CO2 gas exchange. The results indicated that ≤10% of RL results from TCA cycle reactions, which are widely considered to dominate RL. Further analysis of the results indicated that oxidation of glucose-6-phosphate to pentose phosphate via 6-phosphogluconate (the G6P/OPP shunt) can account for >93% of CO2 released by RL.