Interactions between organic and inorganic carbon sources during mixotrophic cultivation of Synechococcus sp.

Glucose at 3 g l(-1) markedly accelerated growth of Synechococcus sp. PCC 7002. The net photosynthesis rate was 263 micromol O2 (mg Chl a h)(-1) for mixotrophic culture and 146 micromol O2 (mg Chl a h)(-1) for photoautotrophic culture. Additing 1 g NaHCO3 l(-1) to the glucose-supplemented culture enhanced the photosynthetic rate by 18%, and the total carbon consumption rate was raised to 2.5 mg l(-1) (mg chl a h)(-1) from a previously negative value. An interaction between organic and inorganic carbon metabolism was established.     

Monoseptic cultivation of phototrophic microorganisms--development and scale-up of a photobioreactor system with thermal sterilization

The use of phototrophic microorganisms as sources of biological active substances in photoautotrophic and mixotrophic cultivation modes requires an adequate cultivation system with thermal sterilization. A corresponding photobioreactor system in the 10, 25 and 100 l scales was developed. This "Medusa"-photobioreactor system represents a concept based on the air-lift loop principle, whose working volume is irradiated by external light sources. The incident irradiation can be varied by a light control system. An effective CO(2)/O(2) gas exchange is enabled due to the efficient supply with process gas by several gas supply nozzles within the system and a large degassing surface. Using a model to describe the growth characteristics of the organisms, the volumetric irradiation coefficient I(DX) was defined as scale-up parameter. On this basis the scale-up from 1 l bubble columns to the 10 and 100 l scales was realized. The scale-up was performed successfully with Chlorella salina as model organism. A maximum biomass concentration of 7.89 g (dry weight) l(-1) at a maximum specific growth rate of 0.058 h(-1) and a yield of 35 mg l(-1) h(-1) was obtained in a batch cultivation in the 100 l scale under photoautotrophic conditions with an initial biomass concentration of approx. 0.03 g l(-1).     

Growth and fatty acid composition of Nannochloropsis sp. grown mixotrophically in fed-batch culture

The cell growth and eicosapentaenoic acid (EPA) yields of Nannochloropsis sp. were enhanced in the fed-batch cultures. With feeding glucose solution, the biomass reached 1.1 g dry wt l(-1) after 10 days' culture, which was 40% higher than that obtained in the batch culture (0.8 g dry wt l(-1)). With supplement of nitrate solution, the biomass reached 1 g dry wt l(-1), and reached the stationary phase 2 days earlier than the others. The maximum of biomass (1.2 g dry wt l(-1)) was obtained with the supplement of the mixture of glucose and nitrate solution. The EPA yields of Nannochloropsis sp. after 10 days' growth in the fed-batch cultures were 52 mg l(-1), 43 mg l(-1) and 56 mg l(-1) with, respectively, addition of nitrate, glucose and both together. In batch culture only 35 mg EPA l(-1) was obtained.     

Growth characteristics of the cyanobacterium Nostoc flagelliforme in photoautotrophic, mixotrophic and heterotrophic cultivation

Nostoc flagelliforme is a terrestrial cyanobacterium with high economic value. Dissociated cells separated from a natural colony of N. flagelliforme were cultivated for 7 days under either phototrophic, mixotrophic or heterotrophic culture conditions. The highest biomass, 1.67 g L⁻¹ cell concentration, was obtained under mixotrophic culture, representing 4.98 and 2.28 times the biomass obtained in phototrophic and heterotrophic cultures, respectively. The biomass in mixotrophic culture was not the sum as that in photoautotrophic and heterotrophic cultures. During the first 4 days of culture, the cell concentration in mixotrophic culture was lower than the sum of those in photoautotrophic and heterotrophic cultures. However, from the 5th day, the cell concentration in mixotrophic culture surpassed the sum of those obtained from the other two trophic modes. Although the inhibitor of photosynthetic electron transport DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] efficiently inhibited autotrophic growth of N. flagelliforme cells, under mixotrophic culture they could grow by using glucose. The addition of glucose changed the response of N.flagelliforme cells to light. The maximal photosynthetic rate, dark respiration rate and light compensation point in mixotrophic culture were higher than those in photoautotrophic cultures. These results suggest that photoautotrophic (photosynthesis) and heterotrophic (oxidative metabolism of glucose) growth interact in mixotrophic growth of N. flagelliforme cells.     

Characteristics of mixotrophic growth of Synechocystis sp. in an enclosed photobioreactor

Synechocystis sp. PCC 6803 was grown in a 2.5 l enclosed photobioreactor on medium with or without glucose. The incident light intensities ranged from 1.5 klux to 7 klux. The highest average specific growth rates of mixotrophic culture and photoautotrophic culture were, respectively, 1.3 h^–1 at a light intensity of 7 klux on 3.2 g l^–1 glucose and 0.3 h^–1 at both light intensities of 5 klux and 7 klux. The highest cell density 2.5 g l ^–1 was obtained at both of light intensities 5 klux and 7 klux on 3.2 g glucose l^–1. Glucose consumption decreased with decreasing light intensity. The energy yields of mixotrophic cultures were 4 to 6 times higher than that of photoautotrophic cultures. Light favored mixotrophic growth of Synechocystis sp. PCC 6803, especially at higher light intensities (5–7 klux).     

葡萄糖对小球藻(Chloralla sp. HN08)光合作用和生长的影响

【目的】探讨葡萄糖作为外加碳源对热带海洋小球藻(Chloralla sp.HN08)生物质生产和脂、光合色素、碳水化合物及可溶性蛋白等细胞主要成份含量的影响。【方法】分析比较小球藻HN08在光合自养和兼养(添加10 g/L葡萄糖)2种营养方式下的生长速率、细胞密度、光合放氧速率、油脂相对含量,以及可溶性总糖、淀粉和可溶性蛋白的含量。【结果】结果表明,在光照条件下葡萄糖(10 g/L)能促进小球藻(Chloralla sp.HN08)生长,提高细胞终密度,而异养条件下藻细胞逐渐衰亡。兼养条件下,细胞相对生长速率及细胞终密度分别是自养条件下的6.8倍和1.3倍。兼养藻细胞中可溶性糖、淀粉、油脂含量显著高于(P0.05)光合自养细胞,然而可溶性蛋白质和光合色素含量显著低于(P0.05)光合自养细胞。添加葡萄糖的小球藻液的光饱和点和呼吸速率均高于光自养条件下的细胞,但2种培养条件下藻液的净光合速率无显著差异(P0.05)。【结论】光照条件下,添加葡萄糖可显著提高小球藻HN08相对生长速率和细胞终密度,促进油脂与淀粉的积累。     

鱼腥藻1017株的混合营养型生长

鱼腥藻１０１７株混合营养型生长有其特点,外源葡萄糖对生长的刺激不仅在低光强（８００ｌｘ）,而且在高光强（７０００ｌｘ）也表现出来。其混合营养型生长速率在８００－７０００ｌｘ范围内随光照强度的增加而增加,在葡萄糖浓度５－２０ｍｍｏｌ／Ｌ范围内随外源葡萄糖浓度增加而增加。鱼腥藻１０１７株混合营养型生长与光能自养生长相比,生长速率明显提高,对数生长期延长,收获物浓度显著增高,生物量显著提高。     

Effects of carbon source and light intensity on the growth and total lipid production of three microalgae under different culture conditions

We attempted to enhance the growth and total lipid production of three microalgal species, Isochrysis galbana LB987, Nannochloropsis oculata CCAP849/1, and Dunaliella salina, which are capable of accumulating high content of lipid in cells. Low nitrogen concentration under photoautotrophic conditions stimulated total lipid production, but a decreasing total lipid content and an increasing biomass were observed with increasing nitrogen concentration. Among the different carbon sources tested for heterotrophic cultivation, glucose improved the growth of all three strains. The optimal glucose concentration for growth of I. galbana LB987 and N. oculata CCAP849/1 was 0.02 M, and that of D. salina was 0.05 M. Enhanced growth occurred when they were cultivated under heterotrophic or mixotrophic conditions compared with photoautotrophic conditions. Meanwhile, high total lipid accumulation in cells occurred when they were cultivated under photoautotrophic or mixotrophic conditions. During mixotrophic cultivation, biomass production was not affected significantly by light intensity; however, both chlorophyll concentration and total lipid content increased dramatically with increasing light intensity up to 150 µmol/m²/s. The amount and composition ratio of saturated and unsaturated fatty acids in cells were different from each other depending on both species and light intensity. The highest accumulation of total fatty acid (C16–C18) among the three strains was found from cells of N. oculata CCAP849/1, which indicates that this species can be used as a source for production of biodiesel.     

Optimization of growth and fatty acid composition of a unicellular marine picoplankton,Nannochloropsis sp., with enriched carbon sources

A unicellular marine picoplankton, Nannochloropsis sp., was grown under CO₂-enriched photoautotrophic or/and acetate-added mixotrophic conditions. Photoautotrophic conditions with enriched CO₂ of 2800 l CO₂ l^–1 and aeration gave the highest biomass yield (634 mg dry wt l^–1), the highest total lipid content (9% of dry wt), total fatty acids (64 mg g^–1 dry wt), polyunsaturated fatty acids (35% total fatty acids) and eicosapentaenoic acid (EPA, 20:53) (16 mg g^–1 dry wt or 25% of total fatty acids). Mixotrophic cultures gave a greater protein content but less carbohydrates. Adding sodium acetate (2 mM) decreased the amounts of the total fatty acids and EPA. Elevation of CO₂ in photoautotrophic culture thus enhances growth and raises the production of EPA in Nannochloropsis sp.     

Effects of organic carbon sources on cell growth and eicosapentaenoic acid content of <Emphasis Type="BoldItalic">Nannochloropsis</Emphasis> sp.

A strain of Nannochloropsis isolated originally from the East China Sea and obtained from Institute of Hydrobiology, Chinese Academy of Sciences was shown to utilize glucose or ethanol for mixotrophic and heterotrophic growth. The highest cell density, 550 mg L^{− 1} dry weight after culture for 8 days, was obtained during mixotrophic culture with 30 mM glucose. The organic carbon sources had no effect on the net photosynthetic rate, but enhanced the respiratory rate. The addition of an organic carbon source led to an increase in the cell lipid content and a decrease in their eicosapentaenoic acid (EPA) content. The EPA yield was 21.9 mg L^{− 1} using photoautotrophic culture, and 23.4 mg L^{− 1} and 23.0 mg L^{− 1}, respectively, in mixotrophic cultivation with glucose or ethanol as the carbon source.     

Phosphate assimilation by Chlorella and adjustment of phosphate concentration in basal medium for its cultivation

Assimilation of phosphate by Chlorella pyrenoidosa was 0.81-8.1 mg PO(4)-P/g dry weight for heterotrophic cultures and 0.81-16.1 mg/g for mixotrophic cultures. Optimal carbon:phosphorous (C/P) ratios were 206:1-2060:1 and 103:1-2060:1 for heterotrophic and mixotrophic cultivations, respectively. These requirements for phosphate for growth of C. pyrenoidosa under either heterotrophic or mixotrophic conditions are much less (6.25-62.5 or 3.12-62.5-fold at 10 g glucose/l) than its concentration in basal medium.     

Relationship Between the Growth of Synechocystis sp. PCC 6803 on Medium with Glucose and the Photosynthetic Energy Transformation

Measurements of chlorophyll fluorescence kinetics from dark-starved cells, light-grown cells and mixotrophic cells of Synechocystis sp. PCC 6803 were obtained using a pulse amplitude modulation (PAM) fluorometer. Photosystem Ⅱ photochemical efficiency Ⅱand the extent of reduction of Q－A in the three kinds of cells described above were compared. The millisecond delayed light emission (MDLE) of light-grown cells and mixotrophic cells were also detected. On the basis of the analysis of fluorescence kinetic parameters, comparison of the slow phase of MDLE and the influence of inhibitors of photosynthetic electron transport3-(3,4-dichlorophenyl)-1,1-dimethylurea(DCMU), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) on the mixotrophic growth of Synechocystis sp. PCC 6803, it was concluded that the reasons for higher growth rate under mixotrophic than that under photoautotrophic might be that glucose promoted the photoautotrophic growth of mixotrephic cells and the donation of eletrons to the plastoquinone pool from the respiratory substance and the transform of energy was promoted by photosynthetic system, which provided the energy needed by anabolism of cells caused by the glucose added to the medium.      

Production potential of eicosapentaenoic acid by the diatom Nitzschia laevis

To investigate the production potential of eicosapentaenoic acid (EPA) by the diatom Nitzschia laevis, the growth characteristics and fatty acid composition of the cells were studied under photoautotrophic, mixotrophic and heterotrophic conditions of growth. The specific growth rate and maximum biomass concentration were respectively 0.466 d^–1 and 2.27 g l^–1 for mixotrophic culture, 0.344 d^–1 and 2.04 g l^–1 for heterotrophic culture, and 0.167 d^–1 and 0.5 g l^–1 for photoautotrophic culture, respectively. As for EPA production, the yield and productivity were respectively 52.32 mg l^–1 and 10.46 mg l^–1 d for mixotrophic culture, 35.08 mg l^–1 and 6.37 mg l^–1 d for heterotrophic culture, and 6.78 mg l^–1 and 3.39 mg l^–1 d for photoautotrophic culture, respectively. Results suggest that mixotrophic culture is the most suitable growth mode for the production of EPA by the diatom Nitzschia laevis. The results are useful for the development of a cost-effective fermentation process for EPA production by Nitzschia laevis.     

聚球藻7942混养培养中碳代谢与能量利用

为了考察聚球藻7942在混养条件下的能量利用效率,分别以葡萄糖和乙酸为碳源开展了聚球藻7942的混养培养研究,并在此基础上利用代谢通量分析方法对聚球藻7942混养条件下的碳代谢和能量利用进行了探讨。结果表明:葡萄糖和乙酸均能促进藻细胞生长,且乙酸促进藻细胞生长的作用更为明显;葡萄糖利用可明显增加藻细胞糖酵解途径中碳代谢流量,而乙酸利用则导致糖酵解途径中碳代谢流量减小,两种有机碳源均增加了柠檬酸循环中碳代谢流量;有机碳源导致藻细胞光化学效率下降,而葡萄糖较之乙酸降低藻细胞光化学效率更为明显。虽然混养条件下光能的贡献率要小于光自养,但基于能量的细胞得率和能量转换率均高于光自养,光自养和以葡萄糖、乙酸为碳源的混养中基于ATP生成的能量转换效率分别为6.81%、7.43%和8.77%。     

Manipulation of nitrogen levels and mode of cultivation are viable methods to improve the lipid,fatty acids,phytochemical content,and bioactivities in Chlorella minutissima

The effect of nitrogen (N: low = 2% N or moderate = 10% N) levels and cultivation (photoautotrophic or mixotrophic) modes on the biochemicals in Chlorella minutissima was evaluated using a mass culture system. Moderate N and mixotrophic cultures had higher biomass, protein, carbohydrate content and photosynthetic pigments than the low N and photoautotrophic treatments. In contrast, lipid and fatty acid content of the low N and photoautotrophic treatments were higher than in the moderate N and mixotrophic cultures. More phytochemicals were accumulated in moderate N and mixotrophic cultures which corresponded to better antioxidant capacity in the extracts. The most potent (0.7 mg · mL^?1) acetylcholinesterase inhibitory activity was displayed by moderate N and mixotrophic treatment. Approximately 60% of the extracts exhibited a noteworthy antimicrobial activity regardless of the N levels and cultivation modes. Thus, moderate N level enhanced the phytochemicals and biological activities of C. minutissima cultured under a mixotrophic system.     

Effects of Glycerol on the Fluorescence Spectra and Chloroplast Ultrastructure of Phaeodactylum tricornutum (Bacillariophyta)

Responses of the photosynthetic activity of Phaeodactylum tricornutum (Bacillariophyta) to organic carbon glycerol were investigated. The growth rate, photosynthetic pigments, 77 K fluorescence spectra, and chloroplast ultrastructure of P. tricornutum were examined under photoautotrophic, mixotrophic, and photoheterotrophic conditions. The results showed that the specific growth rate was the fastest under mixotrophic conditions. The cell photosynthetic pigment content and values of Chl a/Chl c were reduced under mixotrophic and photoheterotrophic conditions. The value of carotenoid/Chl a was enhanced under mixotrophic conditions, but was decreased under photoheterotrophic conditions. In comparison with photoautotrophic conditions, the fluorescence emission peaks and fluorescence excitation peaks were not shifted. The relative fluorescence of photosystem (PS) Ⅰ and PS Ⅱ and the values of F6851F710 and F685/F738 were decreased. Chloroplast thylakoid pairs were less packed under mixotrophic and photoheterotrophic conditions. There was a strong correlation between degree of chloroplast thylakoid packing and the excitation energy kept in PS Ⅱ. These results suggested that the PS Ⅱ activity was reduced by glycerol under mixotrophic conditions, thereby leading to repression of the photosynthetic activity.     

MIXOTROPHIC GROWTH MODIFIES THE RESPONSE OF SPIRULINA (ARTHROSPIRA) PLATENSIS (CYANOBACTERIA) CELLS TO LIGHT

Spirulina (Arthrospira) platensis (Nordstedt) Geitler cells grown under mixotrophic conditions exhibit a modified response to light. The maximal photosynthetic rate and the light saturation value of mixotrophic cultures were higher than those of the photoautotrophic cultures. Dark respiration and light compensation point were also significantly higher in the mixotrophically grown cells. As expected, the mixotrophic cultures grew faster and achieved a higher biomass concentration than the photoautotrophic cultures. In contrast, the growth rate of the photoautotrophic cultures was more sensitive to light. The differences between the two cultures were also apparent in their responses to exposure to high photon flux density of 3000 μmol·m ^{− 2}·s ^{− 1}. The light-dependent O₂ evolution rate and the maximal efficiency of photosystem II photochemistry declined more rapidly in photoautotrophically grown than in mixotrophically grown cells as a result of exposure to high photon flux density. Although both cultures recovered from the high photon flux density stress, the mixotrophic culture recovered faster and to a higher extent. Based on the above results, growth of S. platensis with a fixed carbon source has a significant effect on photosynthetic activity.     

绿色微囊藻的混合营养生长

研究绿色微囊藻(Microcystis viridis)在混合条件下的生长特性,以及葡萄糖,光照强度和pH对绿色微囊藻生长的影响。结果表明:绿色微囊藻混合营养生长与光能自养生长相比,生长速率明显提高,对数期延长,生物量显著提高;随着初始葡萄糖浓度在0~18.0g/l范围内增加,同一光照条件下明显提高了藻细胞的生长速率,但在初始葡萄糖浓度18.0~36.0g/l范围内,同一光照条件下葡萄糖浓度的高低对藻细胞的生长速率不再有更大的影响;在光照强度24~112μE·m^-2·s^-1范围内,初始葡萄糖浓度相同条件下藻细胞的生长速率及对葡萄糖的藻体得率都随光照强度的增强而增大,但当光照强度在112~200μE·m^-2·s^-1时,绿色微囊藻的生长速率增加幅度较小,出现了光饱和现象;当pH处于8.0~10.0间,明显促进了绿色微囊藻的生长,偏离该范围越大,越抑制绿色微囊藻的生长,甚至导致死亡。     

Mixotrophic and photoautotrophic cultivation of 14 microalgae isolates from Saskatchewan, Canada: potential applications for wastewater remediation for biofuel production

Northern regions are generally viewed as unsuitable for microalgal biofuel production due to unfavorable climate and solar insolation levels. However, these conditions can potentially be mitigated by coupling microalgal cultivation to industrial processes such as wastewater treatment. In this study, we have examined the biomass and lipid productivity characteristics of 14 microalgae isolates (Chlorophyta) from the Canadian province of Saskatchewan. Under both photoautotrophic and mixotrophic cultivation, a distinct linear trend was observed between biomass and lipid productivities in the 14 SK isolates. The most productive strain under cultivation in TAP media was Scenedesmus sp.-AMDD which displayed rates of biomass and fatty acid productivities of 80 and 30.7?mg?L^?1?day^?1, respectively. The most productive strain in B3NV media was Chlamydomonas debaryana-AMLs1b which displayed rates of biomass and fatty acid productivities of 51.7 and 5.9?mg?L^?1?day^?1, respectively. In 11 of the isolates tested, secondary municipal wastewater (MCWW) supported rates of biomass productivity between 21 and 33?mg?L^?1?day^?1 with Scenedesmus sp.-AMDD being the most productive. Three strains, Chlamydomonas debaryana-AMB1, Chlorella sorokiniana-RBD8 and Micractinium sp.-RB1b, showed large increases in biomass productivity when cultivated mixotrophically in MCWW supplemented with glycerol. High relative oleic acid content was detected in 10 of the 14 isolates when grown mixotrophically in media supplemented with acetate. There was no detectable effect on the fatty acid profiles in cells cultivated mixotrophically in glycerol-supplemented MCWW. These data indicate that biomass and lipid productivities are boosted by mixotrophic cultivation. Exploiting this response in municipal wastewater is a promising strategy for the production of environmentally sustainable biofuels.     

Effects of additional Mg2+ on the growth,lipid production,and fatty acid composition of Monoraphidium sp. FXY-10 under different culture conditions

The effects of supplementing the culture medium with Mg²⁺ on the growth, lipid production, and fatty acid composition of Monoraphidium sp. FXY-10 were studied under photoautotrophic, heterotrophic, and mixotrophic conditions. Under the photoautotrophic condition, microalgae supplemented with 100 μM Mg²⁺ grew significantly better than the control group and exhibited a secondary growth state. The final cell density was 1.25-fold higher than that of the control group (2.98 g L^?1), and the peak lipid content reached 59.8 % (control group 52.3 %). Culture under the heterotrophic condition did not significantly increase the growth rate, but the experimental group (100 μM Mg²⁺ supplementation) achieved a 37.03 % lipid content compared to 28.47 % by the control group. The lipid productivity of the experimental group (100 μM Mg²⁺ supplementation) was higher, reaching 65.93 mg L^?1 day^?1 compared with 56.10 mg L^?1 day^?1 for the group without additional Mg²⁺. Under the mixotrophic condition, the experimental group achieved a final density of 3.10 g L^?1, which was higher than that of the control group (2.98 g L^?1). There was also no variation in fatty acid composition between the experimental group and the control group. Under the heterotrophic and mixotrophic conditions, the experimental group produced more than 50% saturated fatty and mono-unsaturated fatty acids, and the degree of unsaturation was <137. This result was relatively lower than that of the control.