Cellular Chlorophyll Content Research Articles

Evaluation of the Effect of Growth Factors on Chlorophylls a and b Production from Microalgae.

Microalgae contain two main groups of pigments: chlorophylls and carotenoids. Chlorophyll is a green pigment that absorbs light energy and transforms it into chemical energy to facilitate the synthesis of organic compounds. This pigment serves as a valuable primary source for biotechnological input products in the food, pharmaceutical, and cosmetic industries due to its high antioxidant properties and coloring capabilities. The objective of this research was to evaluate the effect of growth factors (CO2 concentration, light color, and light intensity) through a Taguchi L4 experimental design on cell growth and the cellular content of chlorophyll a and b in Chlorella sorokiniana, followed by validation of the method using Haematococcus pluvialis microalgae as an additional study model. Cell growth was quantified using the optical density spectrophotometric technique at a wavelength of 550 nm. For the quantification of chlorophylls, a cell extract was obtained using a 90% pure acetone solution, and subsequently, the concentrations of chlorophylls a and b were quantified using spectrophotometric techniques at wavelengths of 647 nm and 664 nm, according to the method described by Jeffrey and Humphrey. The experimental results indicated that controlling conditions of low CO2 addition, purple light, and low light intensity increases both cell growth and the concentration of chlorophylls a and b within the cells. The implementation of this chlorophyll quantification method allows for quick, simple, and precise determination of chlorophyll content, as the wavelengths used are at the absorbance peaks of both types of chlorophylls, making this technique easily reproducible for any microalgae under study.

Promoting effects of aluminum addition on chlorophyll biosynthesis and growth of two cultured iron‐limited marine diatoms

AbstractAluminum (Al) may play a role in the ocean's capacity for absorbing atmospheric CO2 via influencing carbon fixation, export, and sequestration. Aluminum fertilization, especially in iron (Fe)‐limited high‐nutrient, low‐chlorophyll ocean regions, has been proposed as a potential CO2 removal strategy to mitigate global warming. However, how Al addition would influence the solubility and bioavailability of Fe as well as the physiology of Fe‐limited phytoplankton has not yet been examined. Here, we show that Al addition (20 and 100 nM) had little influence on the Fe solubility in surface seawater and decreased the Fe bio‐uptake by 11–22% in Fe‐limited diatom Thalassiosira weissflogii in Fe‐buffered media. On the other hand, the Al addition significantly increased the rate of chlorophyll biosynthesis by 45–60% for Fe‐limited T. weissflogii and 81–102% for Fe‐limited Thalassiosira pseudonana, as well as their cell size, cellular chlorophyll content, photosynthetic quantum efficiency (Fv/Fm) and growth rate. Under Fe‐sufficient conditions, the Al addition still led to an increased growth rate, though the beneficial effects of Al addition on chlorophyll biosynthesis were no longer apparent. These results suggest that Al may facilitate chlorophyll biosynthesis and benefit the photosynthetic efficiency and growth of Fe‐limited diatoms. We speculate that Al addition may enhance intracellular Fe use efficiency for chlorophyll biosynthesis by facilitating the superoxide‐mediated intracellular reduction of Fe(III) to Fe(II). Our study provides new evidence and support for the iron–aluminum hypothesis.

Symbiont genus determines the trophic strategy of corals: Implications for intraspecific competition for energy sources in coral reefs

Coral reefs are typically found in nutrient-limited waters, which may restrict the growth and expansion of corals. Nevertheless, corals are mixotrophs that may adjust to the variation in the availability of energy sources by switching their major nutritional mode between autotrophy (i.e., synthesizing their own food by symbionts) and heterotrophy (i.e., consuming external food sources). Such trophic plasticity may, however, be subject to symbiont genus and environmental conditions. Using a widespread coral species (Pocillopora damicornis), we examine how symbiont genus (Cladocopium vs. Durusdinium) affects the physiological traits (biomass, symbiont density, C:N ratio and chlorophyll content) of corals and their trophic strategy across seasons (summer and winter) based on stable isotope markers (δ13C and δ15N). We found that corals dominated by Cladocopium (PdC) had a lower symbiont density, but higher autotrophic capacity (higher cellular chlorophyll content and higher δ13C) than those by Durusdinium (PdD). Across seasons, the trophic strategy of PdC was flexible that the autotrophic capacity was reduced by 37.1 % from summer to winter, whereas the trophic strategy of PdD remained relatively unchanged. PdC had a greater heterotrophic capacity in winter, while PdD in summer. Our findings suggest that symbiont genus can determine the trophic flexibility of corals and drive trophic niche differentiation between conspecific corals. By adaptively changing trophic strategy, intraspecific competition of corals for energy sources can be reduced, possibly allowing them to persist in oligotrophic waters and adapt to the future oceanic climate.

A paler shade of green: engineering cellular chlorophyll content to enhance photosynthesis in crowded environments.

In natural ecosystems, plants compete for space, nutrients and light. The optically dense canopies limit the penetration of photosynthetically active radiation and light often becomes a growth-limiting factor for the understory. The reduced availability of photons in the lower leaf layers is also a major constraint for yield potential in canopies of crop monocultures. Traditionally, crop breeding has selected traits related to plant architecture and nutrient assimilation rather than light use efficiency. Leaf optical density is primarily determined by tissue morphology and by the foliar concentration of photosynthetic pigments (chlorophylls and carotenoids). Most pigment molecules are bound to light-harvesting antenna proteins in the chloroplast thylakoid membranes, where they serve photon capture and excitation energy transfer toward reaction centers of photosystems. Engineering the abundance and composition of antenna proteins has been suggested as a strategy to improve light distribution within canopies and reduce the gap between theoretical and field productivity. Since the assembly of the photosynthetic antennas relies on several coordinated biological processes, many genetic targets are available for modulating cellular chlorophyll levels. In this review, we outline the rationale behind the advantages of developing pale green phenotypes and describe possible approaches toward engineering light-harvesting systems.

Overexpression of GhABF3 increases cotton(Gossypium hirsutum L.) tolerance to salt and drought

BackgroundPlants suffer from various abiotic stresses during their lifetime, of which drought and salt stresses are two main factors limiting crop yield and quality. Previous studies have shown that abscisic acid (ABA) responsive element binding protein (AREB)/ ABRE binding factors (ABFs) in bZIP transcription factors are involved in plant stress response in an ABA-dependent manner. However, little is known about the properties and functions of AREB/ABFs, especially ABF3, in cotton.ResultsHere, we reported the cloning and characterization of GhABF3. Expression of GhABF3 was induced by drought,salt and ABA treatments. Silencing of GhABF3 sensitized cotton to drought and salt stress, which was manifested in decreased cellular antioxidant capacity and chlorophyll content. Overexpression of GhABF3 significantly improved the drought and salinity tolerance of Arabidopsis and cotton. Exogenous expression of GhABF3 resulted in longer root length and less leaf wilting under stress conditions in Arabidopsis thaliana. Overexpressing GhABF3 significantly improved salt tolerance of upland cotton by reducing the degree of cellular oxidation, and enhanced drought tolerance by decreasing leaf water loss rate. The increased expression of GhABF3 up-regulated the transcriptional abundance of downstream ABA-inducible genes under salt stress in Arabidopsis.ConclusionIn conclusion, our results demonstrated that GhABF3 plays an important role in plant drought and salt tolerance. Manipulation of GhABF3 by biotechnology might be an important strategy to alter the stress resistance of cotton.

Light-harvesting complex gene regulation by a MYB-family transcription factor in the marine diatom, Phaeodactylum tricornutum.

Unicellular photoautotrophs adapt to variations in light intensity by changing the abundance of light harvest pigment-protein complexes (LHCs) on time scales ofhours to days. This process requires a feedback signal between the plastid (where light intensity is sensed) to the nucleus (where the genes for LHCs are encoded). The signals must include heretofore unidentified transcription factors that modify the expression level of the LHCs. Analysis of the nuclear genome of the model diatom Phaeodactylum tricornutum revealed that all the lhc genes have potential binding sites for transcription factors belonging to the MYB-family proteins. Functional studies involving antisense RNA interference of a hypothetical protein with a MYB DNA-binding domain were performed. The resultant strains with altered photosynthetic and physiological characteristics lost their ability to acclimate to changes in irradiance; i.e., cellular chlorophyll content became independent of growth irradiance. Our results strongly suggest that the inter-organellar signaling cascade was disrupted, and the cell could no longer communicate the environmental signal from the plastid to the nucleus. Here, we identify, for the first time, an LHC Regulating Myb (LRM) transcription factor, which we propose is involved in lhc gene regulation and photoacclimation mechanisms in response to changes in light intensity.

Photosynthesis, competition, and wastewater treatment characteristics of the microalga Monoraphidium sp. Dek19 at cool temperatures

Monoraphidium sp. Dek19 (M. Dek19) is a versatile cold-adapted microalga suitable for treatment of municipal wastewater and production of biofuels from cellular lipids. This study investigated the growth and photosynthetic properties of M. Dek19 which allow it to phycoremediate effluent under cool conditions. Autotrophic cultures grown in tertiary effluent reached greater cell densities at 10 °C than at 22 °C. At both temperatures, this alga could completely deplete polluting PO43− and NO32− ions during growth to stationary phase. M. Dek19 also grew prolifically in primary effluent from an earlier water treatment stage. NH4+ was removed as an alternate N-source, and algal photosynthesis had potential for energy-saving oxygenation of downstream aerobic treatments, including the activated sludge step. In mixed algal culture at a cool temperature (10 °C), M. Dek19 outcompeted Chlorella sp. However, at 22 °C this advantage was diminished, and the population of M. Dek19 cells declined. Photosynthetic O2 evolution by log-phase M. Dek 19 cells at 22 °C showed light saturation at 100 μmol photons m−2 s−1. At 10 °C, photosynthetic rates were 50% lower, light saturation decreased to 60 μmol photons m−2 s−1, yet the cells grew to higher cell densities under cooler conditions. At stationary phase, maximal photosynthesis declined by 50%, indicating self-shading effects. Concurrently, cellular Chlorophyll (Chl) content increased 2-fold, and Chl a/b ratios increased from 1.7 to 3.72. This indicated an acclimation to lower light penetration as the culture matured. The potential for biofuel production was evident from the elevated neutral lipid content of M. Dek19 as nutrients were depleted from the wastewater. We conclude that M. Dek19 is well-adapted to low temperatures and light levels found in winter at many water treatment facilities in colder climates. Thus, M. Dek19 offers a means to phycoremediate municipal wastewater in geographical areas where outdoor growth of algae has previously been discounted as impractical.

Photoacclimation by phytoplankton determines the distribution of global subsurface chlorophyll maxima in the ocean

Subsurface chlorophyll maxima are widely observed in the ocean, and they often occur at greater depths than maximum phytoplankton biomass. However, a consistent mechanistic explanation for their distribution in the global ocean remains lacking. One possible mechanism is photoacclimation, whereby phytoplankton adjust their cellular chlorophyll content in response to environmental conditions. Here, we incorporate optimality-based photoacclimation theory based on resource allocation trade-off between nutrient uptake and light harvesting capacity into a 3D biogeochemical ocean circulation model to determine the influence of resource allocation strategy on phytoplankton chlorophyll to carbon ratio distributions. We find that photoacclimation is a common driving mechanism that consistently explains observed global scale patterns in the depth and intensity of subsurface chlorophyll maxima across ocean regions. This mechanistic link between cellular-scale physiological responses and the global scale chlorophyll distribution can inform interpretation of ocean observations and projections of phytoplankton responses to climate change.

Effects of shading on photosynthetic characteristics and yield at different growth stages of potato.

We examined the effects of shading photosynthetic characteristics, yield, and tolerance to low light in two potato varieties (Jizhangshu 12 and Jizhangshu 8) at four growth stages (seedling, seedling/budding, budding/early flowering and flowering/harvest). There were three shading treatments (0(CK), 20% and 50%). The results showed that at both 20% and 50% shading rates, the SPAD value (a measure of leaf cellular chlorophyll content) of the two varieties decreased significantly at the seedling stage compared with CK treatment. No significant change in the SPAD value occurred at the seedling/budding stage or the budding/early-flowering stage. However, the SPAD value increased marginally after shading at the initial flowering stage. Under the 50% shading regime, the SPAD values of both varieties followed the same trend as the 20% regime. The range of changes at different growth stages remained similar. The only exception was that shading at the beginning of flowering increased SPAD value. Shading had little effect on leaf stomatal conductance (gs) at each developmental stage. There was no significant difference between all treatments and the control, except that the gsvalue of Jizhangshu 8 decreased significantly (43.9%) compared with the control under 50% shading at the beginning of flowering. After the shading treatment, the intercellular CO2 concentration (Ci) of leaves showed an upward trend. 50% shading at the seedling and seedling/budding stages could significantly increase Ci, but not at other stages. The net photosynthetic rate (Pn) of the four periods were all decreased after 15 d of shading. The Pn reduction of the two varieties, 50% shading, was greater than 20% shading. The decline range of Pn of Jizhangshu 12 was less than that of Jizhangshu 8 at all stages, except for that at the seedling stage. The yield of shading treatments decreased in all four stages, with the decrease rate of 50% shading treatment being greater than that of the 20% shading treatment. 'Jizhangshu 12'was not tolerant to low light at the seedling stage but performed better than 'Jizhangshu 8' at other stages. The comprehensive analysis of two test varieties implied that varieties with strong tolerance to low light experienced a smaller boost in intercellular CO2 concentration and a smaller drop in net photosynthetic rate, stomatal conductance, and yield post-shading.

Complete Replacement of the Galactolipid Biosynthesis Pathway with a Plant-Type Pathway in the Cyanobacterium Synechococcus elongatus PCC 7942.

Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the major components of thylakoid membranes and well-conserved from cyanobacteria to chloroplasts. However, cyanobacteria and chloroplasts synthesize these galactolipids using different pathways and enzymes, but they are believed to share a common ancestor. This fact implies that there was a replacement of the cyanobacterial galactolipid biosynthesis pathway during the evolution of a chloroplast. In this study, we first replaced the cyanobacterial MGDG biosynthesis pathway in a model cyanobacterium, Synechococcus elongatus PCC 7942, with the corresponding plant-type pathway. No obvious phenotype was observed under the optimum growth condition, and the content of membrane lipids was not largely altered in the transformants. We next replaced the cyanobacterial DGDG biosynthesis pathway with the corresponding plant-type pathway using the strain described above and isolated the strain harboring the replaced plant-type pathway instead of the whole galactolipid biosynthesis pathway. This transformant, SeGPT, can grow photoautotrophically, indicating that cyanobacterial galactolipid biosynthesis pathways can be functionally complemented by the corresponding plant-type pathways and that the lipid products MGDG and DGDG, and not biosynthesis pathways, are important. While SeGPT does not show strong growth retardation, the strain has low cellular chlorophyll content but it retained a similar oxygen evolution rate per chlorophyll content compared with the wild type. An increase in total membrane lipid content was observed in SeGPT, which was caused by a significant increase in DGDG content. SeGPT accumulated carotenoids from the xanthophyll groups. These results suggest that cyanobacteria have the capacity to accept other pathways to synthesize essential components of thylakoid membranes.

Rapid and Positive Effect of Bicarbonate Addition on Growth and Photosynthetic Efficiency of the Green Microalgae Chlorella Sorokiniana (Chlorophyta, Trebouxiophyceae)

Bicarbonate ions are the primary source of inorganic carbon for autotrophic organisms living in aquatic environments. In the present study, we evaluated the short-term (hours) effects of sodium bicarbonate (NaHCO3) addition on the growth and photosynthetic efficiency of the green algae Chlorella sorokiniana (211/8k). Bicarbonate was added to nonaxenic cultures at concentrations of 1, 2, and 3 g L−1 leading to a significant increase in biomass especially at the highest salt concentration (3 g L−1) and also showing a bactericidal and bacteriostatic effect that helped to keep a reduced microbial load in the algal culture. Furthermore, bicarbonate stimulated the increase in cellular content of chlorophyll a, improving the photosynthetic performance of cells. Since microalgae of genus Chlorella spp. show great industrial potential for the production of biofuels, nutraceuticals, cosmetics, health, and dietary supplements and the use of bicarbonate as a source of inorganic carbon led to short-term responses in Chlorella sorokiniana, this method represents a valid alternative not only to the insufflation of carbon dioxide for the intensive cultures but also for the production of potentially bioactive compounds in a short period.

EVALUATION OF ARTHROSPIRA SP. GROWTH ABILITY ON HEAVY METAL SALTS AND THEIR EFFECT ON SOME CELLULAR COMPONENTS

rthrospira sp. is an aquatic and photosynthetic microorganism that is extensively employed as a food supplement due to its rich contents of nutrients, proteins, and carbohydrates. In this study, a local strain of cyanobacterium of the genus Arthrospira was isolated from the Iraqi soil, in the region of Mosul city, using the Chu’s Medium No. 10. The growth rate, as well as the effects on biomass and cellular component contents of proteins, carbohydrates, and chlorophyll of this strain, were evaluated on the molasses medium alone or supplemented with iron, copper, nickel, cadmium and cobalt salts after fifteen days of incubation. The results showed that the best growth rate (1.09 OD), the highest value of biomass (120.0 mg/l), proteins content (297.2 mg/l), chlorophyll content (14.9 mg/l) and carbohydrates content (400.0 mg/l) of Arthrospira sp. was achieved after fifteen days of incubation. Generally, it was observed that adding iron, copper, nickel, cadmium, and cobalt salts into the molasses medium increased the contents of biomass, proteins, and carbohydrates of Arthrospira sp.. It was noticed that the highest biomass concentration (1960 mg/l) was obtained when Arthrospira sp. grown on molasses medium supplemented with nickel. Also, none of the metal salts added to the molasses medium increased the protein content of Arthrospira sp.. Conversely, adding copper, nickel, and cobalt to the medium showed an adverse effect on the protein content. It was shown that adding iron metal salts into the molasses medium increased the carbohydrates and the chlorophyll contents of Arthrospira sp.. These results suggest that Arthrospira sp. can be utilized for the bioremediation of heavy metals pollution in the environment and industrial sites.

Algal photophysiology drives darkening and melt of the Greenland Ice Sheet

Blooms of Zygnematophycean "glacier algae" lower the bare ice albedo of the Greenland Ice Sheet (GrIS), amplifying summer energy absorption at the ice surface and enhancing meltwater runoff from the largest cryospheric contributor to contemporary sea-level rise. Here, we provide a step change in current understanding of algal-driven ice sheet darkening through quantification of the photophysiological mechanisms that allow glacier algae to thrive on and darken the bare ice surface. Significant secondary phenolic pigmentation (11 times the cellular content of chlorophyll a) enables glacier algae to tolerate extreme irradiance (up to ∼4,000 µmol photons⋅m-2⋅s-1) while simultaneously repurposing captured ultraviolet and short-wave radiation for melt generation. Total cellular energy absorption is increased 50-fold by phenolic pigmentation, while glacier algal chloroplasts positioned beneath shading pigments remain low-light-adapted (Ek ∼46 µmol photons⋅m-2⋅s-1) and dependent upon typical nonphotochemical quenching mechanisms for photoregulation. On the GrIS, glacier algae direct only ∼1 to 2.4% of incident energy to photochemistry versus 48 to 65% to ice surface melting, contributing an additional ∼1.86 cm water equivalent surface melt per day in patches of high algal abundance (∼104 cells⋅mL-1). At the regional scale, surface darkening is driven by the direct and indirect impacts of glacier algae on ice albedo, with a significant negative relationship between broadband albedo (Moderate Resolution Imaging Spectroradiometer [MODIS]) and glacier algal biomass (R2 = 0.75, n = 149), indicating that up to 75% of the variability in albedo across the southwestern GrIS may be attributable to the presence of glacier algae.

Enhancement of lipid production and energy recovery from the green microalga Chlorella vulgaris by inoculum pretreatment with low-dose cold atmospheric pressure plasma (CAPP)

In the present study, a high-throughput procedure was employed to enhance biodiesel recovery from the green microalga Chlorella vulgaris through pretreatment of inoculum with low doses of cold atmospheric-pressure plasma (CAPP). Pretreatment for 30 s resulted in significant increase in the colony-forming unit (CFU) by 26.6% over the control, and recorded the highest biomass productivity of 0.193 g L−1 d−1. In addition, the average cellular chlorophyll content was 18.7% and 23.3% higher than the control and 60 s, respectively. Moreover, short exposure times (30 and 60 s) significantly increased lipid content by 7.5% and 6.9%, respectively, over the control. Because 30 s pretreatment enhanced both growth and lipid content, the volumetric lipid productivity (40.7 mg L−1 d−1) increased by 16.6% and 17.6% over the control and 60 s, respectively. Interestingly, pretreatment for 60 s showed the maximum fatty acid methyl esters (FAMEs) recovery of 478.7 mg g−1 dw, which confirms lipid accumulation in the form of glycerides due to plasma stress. Therefore, the maximum volumetric FAMEs production (998.1 mg L−1) was recorded in the culture inoculated with 60 s-exposed cells, which was 43.5% and 15.7% higher than that of the control and 30 s, respectively. Overall, pretreatment for 60 s resulted in the maximum gross energy output (GEOAdd) of 10.70 kJ L−1, which was 79.5% higher than that of 30 s. In conclusion, the current study represents a novel approach for sustainable production of biodiesel from microalgae through inoculum exposure to a low-dose of CAPP.

Function of the IsiA pigment-protein complex in vivo.

The acclimation of cyanobacterial photosynthetic apparatus to iron deficiency is crucial for their performance under limiting conditions. In many cyanobacterial species, one of the major responses to iron deficiency is the induction of isiA. The function of the IsiA pigment-protein complex has been the subject of intensive research. In this study of the model Synechocystis sp. PCC 6803 strain, we probe the accumulation of the pigment-protein complex and its effects on in vivo photosynthetic performance. We provide evidence that in this organism the dominant factor controlling IsiA accumulation is the intracellular iron concentration and not photo-oxidative stress or redox poise. These findings support the use of IsiA as a tool for assessing iron bioavailability in environmental studies. We also present evidence demonstrating that the IsiA pigment-protein complex exerts only small effects on the performance of the reaction centers. We propose that its major function is as a storage depot able to hold up to 50% of the cellular chlorophyll content during transition into iron limitation. During recovery from iron limitation, chlorophyll is released from the complex and used for the reconstruction of photosystems. Therefore, the IsiA pigment-protein complex can play a critical role not only when cells transition into iron limitation, but also in supporting efficient recovery of the photosynthetic apparatus in the transition back out of the iron-limited state.

A Toolkit for the Characterization of the Photoprotective Capacity of Green Algae.

While light is a crucial energy source in photosynthetic organisms, if its intensity exceeds their photosynthetic capacity it may cause light-induced damage. A dominant photoprotective mechanism in plants and algae is the qE (quenching of energy), the major component of nonphotochemical quenching (NPQ). qE is a process that dissipates absorbed excitation energy as heat, ensuring cell survival even under adverse conditions. The present protocol gathers together a set of experimental approaches (in vivo chlorophyll fluorescence, western blotting, growth and cellular chlorophyll content at very strong light) that collectively allow for the characterization of the qE capacity of the model green algae Chlamydomonas reinhardtii.

Effect of Salinity on the Growth Parameters of Halotolerant Microalgae, <i>Dunaliella spp.</i>

: Dunaliella strains (T35, T36 and T37) were isolated from saline river of Namibia. The effects of salinity stress on their growth and pigment content was investigated. The specific growth rate (µ) of Dunaliella was established in a controlled environment. NaCl concentration has a strong effect on the growth rate and generation time of these halotolerant microalgae. Dunaliella strains were shown to withstand large variations of salinity of the growth medium, 0.5 - 4.0 M NaCl. The optimum conditions for their growth were 1.0 M NaCl at 30 oC, pH 7.5 to 9.0 and 45 µmol m-2 s-1. Increasing salinity from 1.0 to 4.0 M NaCl decreased cell density by 40 %. Increased cellular chlorophyll content was observed form 2 to 14 days of inoculation for all the three strains investigated. However, after day 10 of inoculation there was no significant difference in the pigment content per cell in all strains (p ≤ 0.05). This study shows that there is a good relationship between growth rate and efficient photosynthetic apparatus during the cultivation.

Differences in the photoacclimation and photoprotection exhibited by two species of the ciguatera causing dinoflagellate genus, Gambierdiscus

In culture, Gambierdiscus spp. have been shown to prefer irradiances that are relatively low (≤250μmol photonsm−2s−1) versus those to which they are frequently exposed to in their natural environment (>500μmol photonsm−2s−1). Although several behavioral strategies for coping with such irradiances have been suggested, it is unclear as to how these dinoflagellates do so on a physiological level. More specifically, how do long term exposures (30days) affect cell size and cellular chlorophyll content, and what is the photosynthetic response to short term, high irradiance exposures (up to 1464μmol photonsm−2s−1)? The results of this study reveal that cell size and chlorophyll content exhibited by G. carolinianus increased with acclimation to increasing photon flux density. Additionally, both G. carolinianus and G. silvae exhibited reduced photosynthetic efficiency when acclimated to increased photon flux density. Photosynthetic yield exhibited by G. silvae was greater than that for G. carolinianus across all acclimation irradiances. Although such differences were evident, both G. carolinianus and G. silvae appear to have adequate biochemical mechanisms to withstand exposure to irradiances exceeding 250μmol photonsm−2s−1 for at least short periods of time following acclimation to irradiances of up to 150μmol photonsm−2s−1.

Removal of the product from the culture medium strongly enhances free fatty acid production by genetically engineered Synechococcus elongatus

BackgroundCyanobacterial mutants engineered for production of free fatty acids (FFAs) secrete the products to the medium and hence are thought to be useful for biofuel production. The dAS1T mutant constructed from Synechococcus elongatus PCC 7942 has indeed a large capacity of FFA production, which is comparable to that of triacylglycerol production in green algae, but the yield of secreted FFAs is low because the cells accumulate most of the FFAs intracellularly and eventually die of their toxicity. To increase the FFA productivity, enhancement of FFA secretion is required.ResultsGrowth of dAS1T cells but not WT cells was inhibited in a liquid medium supplemented with 0.13 g L−1 of palmitic acid. This suggested that when FFA accumulates in the medium, it would inhibit the release of FFA from the cell, leading to FFA accumulation in the cell to a toxic level. To remove FFAs from the medium during cultivation, an aqueous-organic two-phase culture system was developed. When the dAS1T culture was overlaid with isopropyl myristate (IM), the final cell density, cellular chlorophyll content, and the photosynthetic yield of PSII were greatly improved. The total amount of extracellular FFA was more than three times larger than that in the control culture grown without IM, with most of the secreted FFAs being recovered in the IM layer. The cellular FFA content was decreased by more than 85% by the presence of the IM layer. Thus, the two-phase culture system effectively facilitated FFA secretion out of the cell. An average FFA excretion rate of 1.5 mg L−1 h−1 was attained in the 432 h of cultivation, with a total amount of excreted FFA being 0.64 g L−1 of culture. These figures were more than three times higher than those reported previously for the cyanobacteria-based FFA production systems.ConclusionsRemoval of FFA from the culture medium is important for improving the productivity of the FFA production system using cyanobacteria. Further increase in productivity would require an increase in both the rates of FFA production in the cell and active FFA export across the plasma membrane.

The Impact of the Optical Properties and Respiration of Algal Cells with Truncated Antennae on Biomass Production Under Simulated Outdoor Conditions

Background: Previous studies have shown the positive effect of genetically induced antenna truncation on the photosynthetic performance of mutant strains (tla). From the increase of maximum photosynthesis rates per unit chlorophyll under saturating irradiance, it has been concluded that photobioreactors with tla mutants could be operated at higher cell numbers and should show increased biomass production under high irradiance. Objective: The potential of three wild type (WT) strains and one tla mutant of Chlamydomonas reinhardtii to adjust cellular Chlorophyll content (Chlcell) in response to different light conditions and its consequences for the cell physiology was investigated. Results: Under high growth irradiance, some WT strains can achieve a comparable level of antenna reduction as observed in the tla mutant. Respiration and maximum photosynthesis rate showed an inverse correlation with Chlcell independently of whether antenna size reduction was achieved by light adaptation or by genetic transformation. Thus, under diurnal light conditions increased respiratory losses compensate for increased photosynthesis rates and exert negative impact on biomass production. The reduction of Chlcell inevitably resulted in an increase of the absorption efficiency of Chl. This implies that cell number and transparency in a bioreactor cannot be increased to a similar extent as expected from Chlcell reduction. Conclusion: Under natural light conditions, the negative impact of increased respiration and absorptivity of antenna truncated cells has to be taken into account to judge the biomass production potential of antenna truncated alga strains. A further reduction of antenna size beyond the current degree could even decrease biomass productivity. Alternative approaches to increase biomass productivity of photobioreactors are suggested. Keywords: antenna truncation, tla mutants, biomass production, Chlamydomonas reinhardtii Keywords: antenna truncation, tla mutants, biomass production, Chlamydomonas reinhardtii.