Growth model for raceway pond cultivation of Desmodesmus sp. MCC34 isolated from a local water body

Biofuel production by microalgae has the advantage of higher biomass productivity over land crops. The selection of potential microalgae depends on the growth in outdoor mass cultivation during different seasons, which can be predicted by a mathematical model. Here, freshwater green algae were isolated from a local water body in Pilani, Rajasthan, India (geographical coordinates: 28°22′N 75°36′E) and characterized by microscopy and ribosomal RNA analysis. The strain was submitted to the Indian Agricultural Research Institute's microbial culture collection (IARI, India) and identified as Desmodesmus sp. MCC34. This strain, along with a fresh water green algae (Chlorella minutissima), two marine green algae species (Dunaliella salina and Dunaliella tertiolecta) and two nitrogen fixing cyanobacteria (Nostoc muscorum and Anabaena doliolum), were screened for lipid productivity and growth kinetics under culture room and raceway pond conditions. Desmodesmus sp. MCC34 showed the highest specific growth rate (0.26 day^?1), biomass production (1.9 g L^?1) and lipid productivity (103 mg L^?1 day^?1). The optimal temperature and saturating light intensity for maximal growth of Desmodesmus sp. MCC34 were 35 °C and 75 μmol m^?2 s^?1 with molar extinction coefficient of 0.22 m² g^?1, respectively. Desmodesmus sp. MCC34 was then subjected to outdoor cultivation in a 20‐m long raceway pond for 18 days during March and November 2013. The areal biomass productivity and volumetric biomass productivity were 13946.23 kg ha^?1 year^?1 and 56.94 mg L^? 1day^?1 during the month of March, decreasing to 6262.28 kg ha^?1 year^?1 and 25.57 mg L^? 1day^?1 during the month of November. A mathematical model was constructed to explain the relationship between biomass production and growth parameters such as temperature, light intensity and nutrient concentration. The productivity values predicted with the proposed model correspond well with the experimental data, suggesting the validity of the model.     

Biomass and lipid enhancement in Ankistrodesmus sp. cultured with reused and minimal nutrients media

Microalgae are a promising feedstock for biofuel production. Lipid content in microalgae could be enhanced under nutrient depletion. This work investigated the effect of the nutrient on lipid accumulation in Ankistrodesmus sp. culture. Batch cultures were carried out using fresh BG11 medium, and after the harvest, the medium was reused for the next culture; this method was repeated two times. The maximum lipid productivity of 29.75 mg L^?1 day^?1 was obtained from the culture with the second reuse medium. In continuous cultures, Ankistrodesmus sp. was cultured in both fresh and modified BG11 mediums. The modified BG11 medium was adjusted to resemble the content of the first reuse medium. As a comparison between batch and continuous cultures, it was proven that the productivity in the continuous culture was better than in the batch, where the achievable maximum biomass and lipid were 188.30 and 38.32 mg L^?1 day^?1. The maximum lipid content of 34.22% was obtained from the continuous culture at a dilution rate of 0.08 day^?1, whereas the maximum saturated and unsaturated fatty acid productivities of 79.96 and 104.54 mg L^?1 day^?1 were obtained at a dilution rate of 0.16 day^?1.     

Biomass production and fatty acid accumulation in Chlorella sp. (strain DEC1B) isolated from a petrol refinery in Huelva (Spain)

A microalgal strain was established from Cepsa's refinery wastewater treatment plant in Huelva (southwest of Spain). Genetic analysis of the chloroplastic rbcL gene encoding for the large subunit of the ribulose bisphosphate carboxylase enzyme (Rubisco) showed the strain had high homology with other known rbcL sequences of the genus Chlorella. The strain grows well autotrophically in minimum mineral medium, with a growth rate of 0.28 ± 0.012 day^?1 and a biomass productivity of 138.9 ± 6.7 mg L^?1 day^?1. N‐starvation and/or over illumination with 650 µmol photons m^?2 s^?1 of PAR light on the cultures induced a significant increase in the intracellular content of lipids in this microalga. Total lipids were extracted from the strain biomass with 2:1 chloroform‐methanol, and they accounted for approximately 50% of the dry biomass. Polyunsaturated fatty acids (PUFAs) represented 60.4% of the total fatty acids found in the strain, thus making this biomass attractive as a high added‐value product source. The strain was able to grow efficiently in the refinery treated wastewater from which it was isolated, providing an attractive advantage for further development of more sustainable algal biomass production processes at reduced costs close to a petrol refinery area.     

Carbon dioxide utilisation of Dunaliella tertiolecta for carbon bio-mitigation in a semicontinuous photobioreactor

Bio-fixation of carbon dioxide (CO₂) by microalgae has been recognised as an attractive approach to offset anthropogenic emissions. Biological carbon mitigation is the process whereby autotrophic organisms, such as microalgae, convert CO₂ into organic carbon and O₂ through photosynthesis; this process through respiration produces biomass. In this study Dunaliella tertiolecta was cultivated in a semicontinuous culture to investigate the carbon mitigation rate of the system. The algae were produced in 1.2-L Roux bottles with a working volume of 1 L while semicontinuous production commenced on day 4 of cultivation when the carbon mitigation rate was found to be at a maximum for D. tertiolecta. The reduction in CO₂ between input and output gases was monitored to predict carbon fixation rates while biomass production and microalgal carbon content are used to calculate the actual carbon mitigation potential of D. tertiolecta. A renewal rate of 45 % of flask volume was utilised to maintain the culture in exponential growth with an average daily productivity of 0.07 g L^?1 day^?1. The results showed that 0.74 g L^?1 of biomass could be achieved after 7 days of semicontinuous production while a total carbon mitigation of 0.37 g L^?1 was achieved. This represented an increase of 0.18 g L^?1 in carbon mitigation rate compared to batch production of D. tertiolecta over the same cultivation period.     

Outdoor pilot-scale production of Botryococcus braunii in panel reactors

In this paper, the outdoor production of Botryococcus braunii in pilot-scale panel reactors (0.4?m³) is studied under uncontrolled conditions at a location close to the Atacama Desert (Chile). Discontinuous experiments were performed on different dates to determine the feasibility of the culture and the influence of environmental conditions on the system yield. Data showed that solar radiation is a major parameter in determining system yield, the average irradiance inside the culture determining both the growth rate and biomass productivity. A maximum specific growth rate of 0.09?day^?1 and biomass productivity of 0.02?g?L^?1?day^?1 (dry weight) were measured in discontinuous mode, at an average irradiance of 60?μE?m^?2?s^?1. With respect to lipids, a productivity of 2.5?mg?L^?1?day^?1 was obtained under favourable growth conditions; no accumulation of lipids at the stationary phase was observed. To confirm this behaviour, a semicontinuous culture was performed at 0.04?day^?1 in a larger reactor (1?m³). In this experiment, the biomass concentration and productivity was 0.3?g?L^?1 and 0.015?g?L^?1?day^?1, respectively. The lipid content and productivity was 15.6% and 2.4?mg?L^?1?day^?1, respectively, the mean average irradiance inside the reactor being 60?μmol photons?m^?2?s^?1. The light path of the reactor determines the light availability, thus determining also the biomass concentration and productivity of the reactor once the dilution rate is fixed. Experimentally, biomass productivity of 0.015?g?L^?1?day^?1 was determined for a light path of 0.15?m, but this can be increased by more than three times for a light path of 0.1?m. These data confirm that this alga can be produced outdoors in a secure form, the culture yield improving when optimal conditions are applied, the data reported here establishing the starting point for the development of the process.     

Arthrospira platensis biomass with high protein content cultivated in continuous process using urea as nitrogen source

Aims: Arthrospira platensis has been studied for single‐cell protein production because of its biomass composition and its ability of growing in alternative media. This work evaluated the effects of different dilution rates (D) and urea concentrations (N₀) on A. platensis continuous culture, in terms of growth, kinetic parameters, biomass composition and nitrogen removal. Methods and results: Arthrospira platensis was continuously cultivated in a glass‐made vertical column photobioreactor agitated with Rushton turbines. There were used different dilution rates (0·04–0·44 day^?1) and urea concentrations (0·5 and 5 mmol l^?1). With N₀ = 5 mmol l^?1, the maximum steady‐state biomass concentration was1415 mg l^?1, achieved with D = 0·04 day^?1, but the highest protein content (71·9%) was obtained by applying D = 0·12 day^?1, attaining a protein productivity of 106·41 mg l^?1 day^?1. Nitrogen removal reached 99% on steady‐state conditions. Conclusions: The best results were achieved by applying N₀ = 5 mmol l^?1; however, urea led to inhibitory conditions at D ≥ 0·16 day^?1, inducing the system wash‐out. The agitation afforded satisfactory mixture and did not harm the trichomes structure. Significance and Impact of the Study: These results can enhance the basis for the continuous removal of nitrogenous wastewater pollutants using cyanobacteria, with an easily assembled photobioreactor.     

Heterotrophic production of Chlorella sp. TISTR 8990—biomass growth and composition under various production conditions

The green microalga Chlorella sp. TISTR 8990 was grown heterotrophically in the dark using various concentrations of a basal glucose medium with a carbon‐to‐nitrogen mass ratio of 29:1. The final biomass concentration and the rate of growth were highest in the fivefold concentrated basal glucose medium (25 g L^?1 glucose, 2.5 g L^?1 KNO₃) in batch operations. Improving oxygen transfer in the culture by increasing the agitation rate and decreasing the culture volume in 500‐mL shake flasks improved growth and glucose utilization. A maximum biomass concentration of nearly 12 g L^?1 was obtained within 4 days at 300 rpm, 30°C, with a glucose utilization of nearly 76% in batch culture. The total fatty acid (TFA) content of the biomass and the TFA productivity were 102 mg g^?1 and 305 mg L^?1 day^?1, respectively. A repeated fed‐batch culture with four cycles of feeding with the fivefold concentrated medium in a 3‐L bioreactor was evaluated for biomass production. The total culture period was 11 days. A maximum biomass concentration of nearly 26 g L^?1 was obtained with a TFA productivity of 223 mg L^?1 day^?1. The final biomass contained (w/w) 13.5% lipids, 20.8% protein and 17.2% starch. Of the fatty acids produced, 52% (w/w) were saturated, 41% were monounsaturated and 7% were polyunsaturated (PUFA). A low content of PUFA in TFA feedstock is required for producing high quality biodiesel. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1589–1600, 2017     

Productivity of Chlorella sorokiniana in a short light‐path (SLP) panel photobioreactor under high irradiance

Maximal productivity of a 14 mm light‐path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2,100 µmol photons m^?2 s^?1 with red light emitting diodes (LEDs) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37°. Chlorella sorokiniana, a fast‐growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 to 0.26 h^?1. The maximal productivity was reached at a dilution rate of 0.24 h^?1, with a value of 7.7 g dw m^?2 h^?1 (m² of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g dw L^?1 h^?1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L^?1 and the photosynthetic efficiency was 1.0 g dw mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons^?1 which must be related to photosaturation and thermal dissipation of absorbed light energy. Biotechnol. Bioeng. 2009; 104: 352–359 © 2009 Wiley Periodicals, Inc.     

Growth,lipid content,productivity, and fatty acid composition of tropical microalgae for scale‐up production

Biomass and lipid productivity, lipid content, and quantitative and qualitative lipid composition are critical parameters in selecting microalgal species for commercial scale‐up production. This study compares lipid content and composition, and lipid and biomass productivity during logarithmic, late logarithmic, and stationary phase of Nannochloropsis sp., Isochrysis sp., Tetraselmis sp., and Rhodomonas sp. grown in L1‐, f/2‐, and K‐medium. Of the tested species, Tetraselmis sp. exhibited a lipid productivity of 3.9–4.8 g m^?2 day^?1 in any media type, with comparable lipid productivity by Nannochloropsis sp. and Isochrysis sp. when grown in L1‐medium. The dry biomass productivity of Tetraselmis sp. (33.1–45.0 g m^?2 day^?1) exceeded that of the other species by a factor 2–10. Of the organisms studied, Tetraselmis sp. had the best dry biomass and/or lipid production profile in large‐scale cultures. The present study provides a practical benchmark, which allows comparison of microalgal production systems with different footprints, as well as terrestrial systems. Biotechnol. Bioeng. 2010;107: 245–257. © 2010 Wiley Periodicals, Inc.     

Effect of nitrate on lipid production by T. suecica, M. contortum, and C. minutissima

Microalgae are an alternative and sustainable source of lipids that can be used as a feedstock for biodiesel production. Nitrate is a good nitrogen source for many microalgae and affects biomass and lipid yields of microalgae. In this study, the effect of nitrate on cell growth and lipid production and composition in Monoraphidium contortum, Tetraselmis suecica, and Chlorella minutissima was investigated. Nitrate affected the production of biomass and the production and composition of lipids of the three microalgae tested. Increasing the nitrate concentration in the culture medium resulted in increased biomass production and higher biomass productivity. Furthermore, increasing the nitrate concentration resulted in a reduction in lipid content and productivity in M. contortum; however, the opposite effect was observed in T. suecica and C. minutissima cultures. C. minutissima and M. contortum lipids contain high levels of oleic acid, with values ranging from 26 to 45.7% and 36.4 to 40.1%, respectively. The data suggest that because of its high lipid productivity (13.79 mg L^?1 d^?1) and high oleic acid productivity (3.78 mg L^?1 d^?1), Chlorella minutissima is a potential candidate for the production of high quality biodiesel.     

High‐yield secretion of recombinant proteins expressed in tobacco cell culture with a designer glycopeptide tag: Process development

Low‐yield protein production remains the most significant economic hurdle with plant cell culture technology. Fusions of recombinant proteins with hydroxyproline‐O‐glycosylated designer glycopeptide tags have consistently boosted secreted protein yields. This prompted us to study the process development of this technology aiming to achieve productivity levels necessary for commercial viability. We used a tobacco BY‐2 cell culture expressing EGFP as fusion with a glycopeptide tag comprised of 32 repeat of ”Ser‐Pro“ dipeptide, or (SP)₃₂, to study cell growth and protein secretion, culture scale‐up, and establishment of perfusion cultures for continuous production. The BY‐2 cells accumulated low levels of cell biomass (～7.5 g DW/L) in Schenk & Hildebrandt medium, but secreted high yields of (SP)₃₂‐tagged EGFP (125 mg/L). Protein productivity of the cell culture has been stable for 6.0 years. The BY‐2 cells cultured in a 5‐L bioreactor similarly produced high secreted protein yield at 131 mg/L. Successful operation of a cell perfusion culture for 30 days was achieved under the perfusion rate of 0.25 and 0.5 day^?1, generating a protein volumetric productivity of 17.6 and 28.9 mg/day/L, respectively. This research demonstrates the great potential of the designer glycopeptide technology for use in commercial production of valuable proteins with plant cell cultures.     

Production of juvenile salmonids in small Norwegian streams is affected by agricultural land use

1. We estimated the biomass and production of juvenile anadromous brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) (parr) in 12 streams in the Skagerrak area of Norway to identify controlling environmental factors, such as land‐use and water chemistry. 2. Production estimates correlated positively with fish density in early summer, but not with the size of the catchment. The summer biomass of age‐0 brown trout and Atlantic salmon was smaller than that of age‐1 and constituted 27.4 and 25.7%, respectively, of the total biomass of the two groups. 3. Mean production of brown trout from July to September varied between streams, but in most cases it was below 2 g 100 m^?2 day^?1. Yearly cohort production from age‐0 in July to age‐1 in July was 10 g m^?2 or less, with mean annual production of 1.32 g 100 m^?2 day^?1, equivalent to 4.8 g m^?2 year^?1. The corresponding annual cohort production of Atlantic salmon was 0.38 g 100 m^?2 day^?1 or 1.4 g m^?2 year^?1. Annual production to biomass ratio (P/B) for brown trout of the same cohort in the various streams was between 1.47 and 4.37; the overall mean (±SD) for all streams was 2.25 ± 0.94. Mean turnover rate of Atlantic salmon was 2.73 ± 0.24. 4. Production of 0+ brown trout during the summer correlated significantly with the percentage of agricultural land and forest/bogs in the catchment, with maxima at 20 and 75%, respectively. Age‐0 brown trout production also correlated with concentration of nitrogen and calcium in the water, with maxima at 2.4 and 14 mg L^?1, respectively. 5. The results support the hypothesis that brown trout parr production reflects the quality of their habitat, as indicated by the dome‐shaped relationship between percentage of agricultural land and the concentration of nitrogen and calcium in the water.     

Culture of microalgae Chlorella minutissima for biodiesel feedstock production

Microalgae are among the most promising of non‐food based biomass fuel feedstock alternatives. Algal biofuels production is challenged by limited oil content, growth rate, and economical cultivation. To develop the optimum cultivation conditions for increasing biofuels feedstock production, the effect of light source, light intensity, photoperiod, and nitrogen starvation on the growth rate, cell density, and lipid content of Chlorella minutissima were studied. The fatty acid content and composition of Chlorella minutissima were also investigated under the above conditions. Fluorescent lights were more effective than red or white light‐emitting diodes for algal growth. Increasing light intensity resulted in more rapid algal growth, while increasing the period of light also significantly increased biomass productivity. Our results showed that the lipid and triacylglycerol content were increased under N starvation conditions. Thus, a two‐phase strategy with an initial nutrient‐sufficient reactor followed by a nutrient deprivation strategy could likely balance the desire for rapid and high biomass generation (124 mg/L) with a high oil content (50%) of Chlorella minutissima to maximize the total amount of oil produced for biodiesel production. Moreover, methyl palmitate (C16:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl linolenate (C18:3) are the major components of Chlorella minutissima derived FAME, and choice of light source, intensity, and N starvation impacted the FAME composition of Chlorella minutissima. The optimized cultivation conditions resulted in higher growth rate, cell density, and oil content, making Chlorella minutissima a potentially suitable organism for biodiesel feedstock production. Biotechnol. Bioeng. 2011;108: 2280–2287. © 2011 Wiley Periodicals, Inc.     

Effect of light emitting diodes on the cultivation of Spirulina platensis using NPK‐10:26:26 complex fertilizer

NPK‐10:26:26 complex fertilizer based culture medium was studied for the mass production of Spirulina platensis using different light emitting diodes (LEDs). First, cultivation was carried out under white LED to formulate the optimum fertilizer loading for which Spirulina growth was maximized. Optimum composition for newly formulated fertilizer medium was NPK fertilizer ?0.76 g L^?1 and sodium bicarbonate ?10.0 g L^?1 and corresponding biomass productivity was found to be 76.67 mg L^?1 day^?1. The effect of different LEDs (for example, blue, white, red, green and yellow) on Spirulina growth kinetics and the accumulation of chlorophyll, protein and lipid content was determined using the optimum NPK fertilizer medium. Kinetic parameters (i.e., biomass productivity, maximum specific growth rate, maximum biomass concentration, nitrogen‐to‐biomass conversion factor and phosphorus‐to‐biomass conversion factor) and chlorophyll accumulation were affected by the use of different LEDs and follow the following trend: blue > white > red > green > yellow, whereas protein and lipid accumulation was almost independent of LEDs used. Elemental C, N, P and K concentrations were measured to find the effects of nutrients for the growth of Spirulina platensis. Physicochemical parameters (pH and conductivity) were also monitored during biomass growth under different LEDs. Finally, biomass growth using NPK‐10:26:26 fertilizer under different LEDs was compared with standard Zarrouk medium and better growth results were obtained using optimally formulated NPK‐10:26:26 fertilizer medium.     

Biomass production of hairy roots of Artemisia annua and Arachis hypogaea in a scaled‐up mist bioreactor

Hairy roots have the potential to produce a variety of valuable small and large molecules. The mist reactor is a gas phase bioreactor that has shown promise for low‐cost culture of hairy roots. Using a newer, disposable culture bag, mist reactor performance was studied with two species, Artemisia annua L. and Arachis hypogaea (peanut), at scales from 1 to 20 L. Both species of hairy roots when grown at 1 L in the mist reactor showed growth rates that surpassed that in shake flasks. From the information gleaned at 1 L, Arachis was scaled further to 4 and then 20 L. Misting duty cycle, culture medium flow rate, and timing of when flow rate was increased were varied. In a mist reactor increasing the misting cycle or increasing the medium flow rate are the two alternatives for increased delivery of liquid nutrients to the root bed. Longer misting cycles beyond 2–3 min were generally deemed detrimental to growth. On the other hand, increasing the medium flow rate to the sonic nozzle especially during the exponential phase of root growth (weeks 2–3) was the most important factor for increasing growth rates and biomass yields in the 20 L reactors. A. hypogaea growth in 1 L reactors was µ = 0.173 day^?1 with biomass yield of 12.75 g DW L^?1. This exceeded that in shake flasks at µ = 0.166 day^?1 and 11.10 g DW L^?1. Best growth rate and biomass yield at 20 L was µ = 0.147 and 7.77 g DW L^?1, which was mainly achieved when medium flow rate delivery was increased. The mist deposition model was further evaluated using this newer reactor design and when the apparent thickness of roots (+hairs) was taken into account, the empirical data correlated with model predictions. Together these results establish the most important conditions to explore for future optimization of the mist bioreactor for culture of hairy roots. Biotechnol. Bioeng. 2010;107: 802–813. © 2010 Wiley Periodicals, Inc.     

Impact of light quality on a native Louisiana Chlorella vulgaris/Leptolyngbya sp. co‐culture

Light effect on cultures of microalgae has been studied mainly on single species cultures. Cyanobacteria have photosynthetic pigments that can capture photons of wavelengths not available to chlorophylls. A native Louisiana microalgae (Chlorella vulgaris ) and cyanobacteria (Leptolyngbya sp.) co‐culture was used to study the effects of light quality (blue–467 nm, green–522 nm, red–640 nm and white–narrow peak at 450 nm and a broad range with a peak at 550 nm) at two irradiance levels (80 and 400 μmol m^?2 s^?1) on the growth, species composition, biomass productivity, lipid content and chlorophyll‐a production. The co‐culture shifted from a microalgae dominant culture to a cyanobacteria culture at 80 μmol m^?2 s^?1. The highest growth for the cyanobacteria was observed at 80 μmol μmol m^?2 s^?1 and for the microalgae at 400 μmol m^?2 s^?1. Red light at 400 μmol m^?2 s^?1 had the highest growth rate (0.41 d^?1), biomass (913 mg L^?1) and biomass productivity (95 mg L^?1 d^?1). Lipid content was similar between all light colors. Green light had the highest chlorophyll‐a content (1649 μg/L). These results can be used to control the species composition of mixed cultures while maintaining their productivity.     

Improvement of both lipid and biomass productivities of Qatar Chlorocystis isolate for biodiesel production and food security

Microalgae are considered a very promising alternative for biofuel production. Several strategies were developed to modulate and improve algae metabolites production to meet the requirements for biodiesel production. Most previous research evidenced that the increase of the lipid content is accompanied by a decrease of the biomass production, which increases the cost of the downstream processing. Hence, the challenge is to find special culture conditions that increase the lipid and the biomass productivities simultaneously. In the present work, we developed a strategy for the improvement of biomass and lipid productivities in a novel local microalga isolate, Chlorocystis sp. QUCCCM14, which was not previously known as a promising strain. Indeed, culturing QUCCCM14 using f/2 medium with 10× NaH₂PO₄ (0.15 g L^?1 NaNO₃ and 5.6 mg L^?1 NaH₂PO₄) resulted in an improvement of 3.178 folds the lipid productivity reaching 56.121 mg L^?1 day^?1 and enhanced the biomass productivity reaching 141.363 mg L^?1 day^?1, simultaneously. Comparative analyses of the FAME profiles demonstrated that fed‐batch culture with phosphate or nitrate separately leads to a high production of the omega 3 fatty acids (Linolenic acid), whereas fed‐batch culture with phosphate and nitrate simultaneously increased the production of fatty acids suitable for biodiesel production.     

Investigation of biomass concentration,lipid production,and cellulose content in Chlorella vulgaris cultures using response surface methodology

The microalgae Chlorella vulgaris produce lipids that after extraction from cells can be converted into biodiesel. However, these lipids cannot be efficiently extracted from cells due to the presence of the microalgae cell wall, which acts as a barrier for lipid removal when traditional extraction methods are employed. Therefore, a microalgae system with high lipid productivity and thinner cell walls could be more suitable for lipid production from microalgae. This study addresses the effect of culture conditions, specifically carbon dioxide and sodium nitrate concentrations, on biomass concentration and the ratio of lipid productivity/cellulose content. Optimization of culture conditions was done by response surface methodology. The empirical model for biomass concentration (R² = 96.0%) led to a predicted maximum of 1123.2 mg dw L^?1 when carbon dioxide and sodium nitrate concentrations were 2.33% (v/v) and 5.77 mM, respectively. For lipid productivity/cellulose content ratio (R² = 95.2%) the maximum predicted value was 0.46 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 when carbon dioxide concentration was 4.02% (v/v) and sodium nitrate concentration was 3.21 mM. A common optimum point for both variables (biomass concentration and lipid productivity/cellulose content ratio) was also found, predicting a biomass concentration of 1119.7 mg dw L^?1 and lipid productivity/cellulose content ratio of 0.44 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 for culture conditions of 3.77% (v/v) carbon dioxide and 4.01 mM sodium nitrate. The models were experimentally validated and results supported their accuracy. This study shows that it is possible to improve lipid productivity/cellulose content by manipulation of culture conditions, which may be applicable to any scale of bioreactors. Biotechnol. Bioeng. 2013; 110: 2114–2122. © 2013 Wiley Periodicals, Inc.     

Increases in benthic community production and metabolism in response to marine‐derived nutrients from spawning Atlantic salmon (Salmo salar)

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Kinetics of growth, oxygen uptake, and substrate utilization of wild type and genetically engineeredBurkholderia sp

The gene (vgb) encoding the hemoglobin (VHb) ofVitreoscilla sp. was cloned intoBurkholderia sp. and the effect of VHb on the growth characteristics of genetically engineeredBurkholderia (YV1) were compared with wild typeBurkholderia (R34) using continuous flow reactors (chemostat) at various dilution rates under aerobic conditions. Batch oxygen uptake rate showed that YV1 has much higher oxygen uptake rate than R34 (i.e. 0.63 mg O₂/g biomass/min vs. 1.43 mg O₂/g biomass/min for R34 and YV1 respectively at a dilution rate of 1.2 day⁻¹). Monod parameters, maximum growth rate (μ_max) and half saturation coefficient (K_s) were found to be 7.03 day⁻¹ and 691 mg/L for R34 respectively, compared to 5.49 day⁻¹ and 404 mg/L for YV1 respectively. At low dilution rates (<2.5 day⁻¹), when the substrate is present in low concentrations, the growth yield was much higher in YV1 (0.52) than in R34 (0.37). Although substrate utilization rates were similar between R34 and YV1, the latter showed much higher oxygen uptake rate than did R34 at all dilution rates. When the stability of VHb was tested on agar plates containing 40 μg/L of kanamycin and 100 μg/L of ampicillin,vgb gene containing VHb plasmid in YV1 was stable over 82 days. When survivability under oxygen limited conditions was tested, R34 survived only for 11 days whereas YV1 survived over 25 days in liquid media; in agar plate experiments, R34 did not survive more than 40 days whereas more than 75% of YV1 survived over 110 days.