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Patrick J McGinn, Scott P MacQuarrie, Jerome Choi, Boris Tartakovsky
In this study, production of the microalga Scenedesmus AMDD in a 300 L continuous flow photobioreactor was maximized using an online flow (dilution rate) control algorithm. To enable online control, biomass concentration was estimated in real time by measuring chlorophyll-related culture fluorescence. A simple microalgae growth model was developed and used to solve the optimization problem aimed at maximizing the photobioreactor productivity. When optimally controlled, Scenedesmus AMDD culture demonstrated an average volumetric biomass productivity of 0...
January 2017: Bioprocess and Biosystems Engineering
Hugh Douglas Goold, Stéphan Cuiné, Bertrand Légeret, Yuanxue Liang, Sabine Brugière, Pascaline Auroy, Hélène Javot, Marianne Tardif, Brian Jones, Fred Beisson, Gilles Peltier, Yonghua Li-Beisson
Enriching algal biomass in energy density is an important goal in algal biotechnology. Nitrogen (N) starvation is considered the most potent trigger of oil accumulation in microalgae and has been thoroughly investigated. However, N starvation causes the slow down and eventually the arrest of biomass growth. In this study, we show that exposing a Chlamydomonas reinhardtii culture to saturating light (SL) under a nonlimiting CO2 concentration in turbidostatic photobioreactors induces a sustained accumulation of lipid droplets (LDs) without compromising growth, which results in much higher oil productivity than N starvation...
August 2016: Plant Physiology
Zinaida Eltsova, Maxim Bolshakov, Anatoly Tsygankov
The composition of photosynthetic apparatus of Rhodobacter sphaeroides wild strain 2.4.1 and its LHII-deficient mutant DBCΩ was compared. The absence of LHII in the mutant was confirmed by comparison of chromatophores spectra and by the absence of electrophoretic band corresponding to LHII complex. Continuous turbidostat cultures of wild strain and its LHII-deficient mutant were compared in response to different light intensities. Cultures were grown using lactate, mixture of lactate and acetate or succinate as carbon source...
December 2016: Photosynthesis Research
Dominick Matteau, Vincent Baby, Stéphane Pelletier, Sébastien Rodrigue
BACKGROUND: Continuous culture devices can be used for various purposes such as establishing reproducible growth conditions or maintaining cell populations under a constant environment for long periods. However, commercially available instruments are expensive, were not designed to handle small volumes in the milliliter range, and can lack the flexibility required for the diverse experimental needs found in several laboratories. METHODOLOGY/PRINCIPAL FINDINGS: We developed a versatile continuous culture system and provide detailed instructions as well as a graphical user interface software for potential users to assemble and operate their own instrument...
2015: PloS One
Pascal van Alphen, Klaas J Hellingwerf
The cyanobacterial circadian clock has been well-studied and shown to be both robust and a dominant factor in the control of gene expression in Synechococcus elongatus PCC7942. In Synechocystis sp. PCC6803, the circadian clock is assumed to function similarly, yet appears to control transcription to a far lesser extent and its circadian rhythm was reported to not be sustained, or at least rapidly damped, under continuous illumination. One of the feedback loops that governs the clock in S. elongatus in addition to the core oscillator, i...
2015: PloS One
Victoria H Work, Matthew R Melnicki, Eric A Hill, Fiona K Davies, Leo A Kucek, Alexander S Beliaev, Matthew C Posewitz
The cyanobacterium Synechococcus sp. Pasteur culture collection 7002 was genetically engineered to synthesize biofuel-compatible medium-chain fatty acids (FAs) during photoautotrophic growth. Expression of a heterologous lauroyl-acyl carrier protein (C12:0-ACP) thioesterase with concurrent deletion of the endogenous putative acyl-ACP synthetase led to secretion of transesterifiable C12:0 FA in CO2-supplemented batch cultures. When grown at steady state over a range of light intensities in a light-emitting diode turbidostat photobioreactor, the C12-secreting mutant exhibited a modest reduction in growth rate and increased O2 evolution relative to the wild-type (WT)...
2015: Frontiers in Bioengineering and Biotechnology
Ali Mohagheghi, Jeffrey G Linger, Shihui Yang, Holly Smith, Nancy Dowe, Min Zhang, Philip T Pienkos
BACKGROUND: Complete conversion of the major sugars of biomass including both the C5 and C6 sugars is critical for biofuel production processes. Several inhibitory compounds like acetate, hydroxymethylfurfural (HMF), and furfural are produced from the biomass pretreatment process leading to 'hydrolysate toxicity,' a major problem for microorganisms to achieve complete sugar utilization. Therefore, development of more robust microorganisms to utilize the sugars released from biomass under toxic environment is critical...
2015: Biotechnology for Biofuels
Hans C Bernstein, Allan Konopka, Matthew R Melnicki, Eric A Hill, Leo A Kucek, Shuyi Zhang, Gaozhong Shen, Donald A Bryant, Alexander S Beliaev
Synechococcus sp. PCC 7002 was grown to steady state in optically thin turbidostat cultures under conditions for which light quantity and quality was systematically varied by modulating the output of narrow-band LEDs. Cells were provided photons absorbed primarily by chlorophyll (680 nm) or phycocyanin (630 nm) as the organism was subjected to four distinct mono- and dichromatic regimes. During cultivation with dichromatic light, growth rates were generally proportional to the total incident irradiance at values <275 μmol photons m(-2) · s(-1) and were not affected by the ratio of 630:680 nm wavelengths...
2014: Frontiers in Microbiology
David Gresham, Maitreya J Dunham
Studying evolution in the laboratory provides a means of understanding the processes, dynamics and outcomes of adaptive evolution in precisely controlled and readily replicated conditions. The advantages of experimental evolution are maximized when the selection is well defined, which enables linking genotype, phenotype and fitness. One means of maintaining a defined selection is continuous culturing: chemostats enable the study of adaptive evolution in constant nutrient-limited environments, whereas cells in turbidostats evolve in constant nutrient abundance...
December 2014: Genomics
Chris N Takahashi, Aaron W Miller, Felix Ekness, Maitreya J Dunham, Eric Klavins
Engineered biological circuits are often disturbed by a variety of environmental factors. In batch culture, where the majority of synthetic circuit characterization occurs, environmental conditions vary as the culture matures. Turbidostats are powerful characterization tools that provide static culture environments; however, they are often expensive, especially when purchased in custom configurations, and are difficult to design and construct in a lab. Here, we present a low cost, open source multiplexed turbidostat that can be manufactured and used with minimal experience in electrical or software engineering...
January 16, 2015: ACS Synthetic Biology
Kieu-Van Dang, Julie Plet, Dimitri Tolleter, Martina Jokel, Stéphan Cuiné, Patrick Carrier, Pascaline Auroy, Pierre Richaud, Xenie Johnson, Jean Alric, Yagut Allahverdiyeva, Gilles Peltier
During oxygenic photosynthesis, metabolic reactions of CO2 fixation require more ATP than is supplied by the linear electron flow operating from photosystem II to photosystem I (PSI). Different mechanisms, such as cyclic electron flow (CEF) around PSI, have been proposed to participate in reequilibrating the ATP/NADPH balance. To determine the contribution of CEF to microalgal biomass productivity, here, we studied photosynthesis and growth performances of a knockout Chlamydomonas reinhardtii mutant (pgrl1) deficient in PROTON GRADIENT REGULATION LIKE1 (PGRL1)-mediated CEF...
July 2014: Plant Cell
K L Larsen, R P Cox, M Miller
Green photosynthetic bacteria contain a mixture of stereoisomers and homologs of their major light harvesting pigment, bacteriochlorophyll (BChl)c. We have determined the distribution of photosynthetic pigments in the green filamentous bacteriumChloroflexus aurantiacus grown in turbidostat culture under light-limited conditions at 5 different illumination intensities. Pigments were extracted from isolated cells, analyzed by HPLC, and the homologs of BChlc identified by their mass spectra. The ratio between BChlc, BChla and carotenoid remained constant at low illumination intensities; at higher intensities BChla and carotenoid increased in parallel compared to BChlc...
July 1994: Photosynthesis Research
J Myers
This account is focused upon the early part of my career in order to illuminate the logistics and the culture of our science in the period 1936 to 1949. A roundabout path took me from a farm in Pennsylvania to a PhD under George Burr at Minnesota in 1939. In studying the photosynthetic competence of chlorophyll formed by the green alga Chlorella in darkness, I stumbled upon the phenomenon of photoinhibition. In a two-year postdoctorate at the Smithsonian Institution, I worked under E.D. McAlister. Our major accomplishment was in making simultaneous recordings of fluorescence and CO2 uptake during the induction period...
December 1996: Photosynthesis Research
Anne J Klok, Johannes A Verbaanderd, Packo P Lamers, Dirk E Martens, Arjen Rinzema, René H Wijffels
A kinetic model is presented that describes functional biomass, starch and storage lipid (TAG) synthesis in the microalga Neochloris oleoabundans as a function of nitrogen and light supply rates to a nitrogen-limited turbidostat cultivation system. The model is based on the measured electron distribution in N. oleoabundans, which showed that starch is the primary storage component, whereas TAG was only produced after an excess of electrons was generated, when growth was limited by nitrogen supply. A fixed 8...
October 2013: Bioresource Technology
Matthew R Melnicki, Grigoriy E Pinchuk, Eric A Hill, Leo A Kucek, Sergey M Stolyar, Jim K Fredrickson, Allan E Konopka, Alexander S Beliaev
A custom photobioreactor was designed to enable automatic light adjustments using computerized feedback control. The system consisted of a 7.5-L cylindrical vessel and an aluminum enclosure housing quantum sensors and light-emitting diode arrays, which provide 630 or 680 nm light to preferentially excite the major cyanobacterial pigments, phycocyanin and/or chlorophyll a, respectively. Custom-developed software rapidly measures light transmission and subsequently adjusts the irradiance to maintain a defined light profile to compensate for culture dynamics, biomass accumulation, and pigment adaptations during physiological transitions, thus ensuring appropriate illumination across batch and continuous growth modes...
April 2013: Bioresource Technology
Erdal Toprak, Adrian Veres, Sadik Yildiz, Juan M Pedraza, Remy Chait, Johan Paulsson, Roy Kishony
We present a protocol for building and operating an automated fluidic system for continuous culture that we call the 'morbidostat'. The morbidostat is used to follow the evolution of microbial drug resistance in real time. Instead of exposing bacteria to predetermined drug environments, the morbidostat constantly measures the growth rates of evolving microbial populations and dynamically adjusts drug concentrations inside culture vials in order to maintain a constant drug-induced inhibition. The growth rate measurements are done using an optical detection system that is based on measuring the intensity of back-scattered light from bacterial cells suspended in the liquid culture...
March 2013: Nature Protocols
G Ullman, M Wallden, E G Marklund, A Mahmutovic, Ivan Razinkov, J Elf
We have developed a method combining microfluidics, time-lapsed single-molecule microscopy and automated image analysis allowing for the observation of an excess of 3000 complete cell cycles of exponentially growing Escherichia coli cells per experiment. The method makes it possible to analyse the rate of gene expression at the level of single proteins over the bacterial cell cycle. We also demonstrate that it is possible to count the number of non-specifically DNA binding LacI-Venus molecules using short excitation light pulses...
February 5, 2013: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Carsten Vejrazka, Marcel Janssen, Giulia Benvenuti, Mathieu Streefland, René H Wijffels
As a result of mixing and light attenuation in a photobioreactor (PBR), microalgae experience light/dark (L/D) cycles that can enhance PBR efficiency. One parameter which characterizes L/D cycles is the duty cycle; it determines the time fraction algae spend in the light. The objective of this study was to determine the influence of different duty cycles on oxygen yield on absorbed light energy and photosynthetic oxygen evolution. Net oxygen evolution of Chlamydomonas reinhardtii was measured for four duty cycles (0...
February 2013: Applied Microbiology and Biotechnology
Bingtuan Li
A model of competition in a turbidostat between two species for an inhibitory growth-limiting nutrient is considered. It is shown that the model has rich dynamics. A coexistence equilibrium and the washout equilibrium can be asymptotically stable simultaneously so that coexistence may depend on initial conditions. Under certain conditions, periodic coexistence of the two species occurs. There is a possibility that two species coexist, whereas one species dies out in the absence of its rival.
April 2008: Journal of Biological Dynamics
Sayam Raso, Bernard van Genugten, Marian Vermuë, René H Wijffels
In large-scale microalgal production in tubular photobioreactors, the build-up of O(2) along the tubes is one of the major bottlenecks to obtain high productivities. Oxygen inhibits the growth, since it competes with carbon dioxide for the Rubisco enzyme involved in the CO(2) fixation to generate biomass. The effect of oxygen on growth of Nannochloropsis sp. was experimentally determined in a fully controlled flat-panel photobioreactor operated in turbidostat mode using an incident photon flux density of 100 μmol photons m(-2) s(-1) and with only the oxygen concentration as variable parameter...
August 2012: Journal of Applied Phycology
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