Effects of different phosphorus concentrations on growth and biochemical composition of Desmodesmus communis (E.Hegewald) E.Hegewald.

The members of the family Scenedesmaceae has the most widely used microalgae species in algal biotechnology studies because of their fast growth rate, quality of nutrition content and lipid accumulation under nutrient-limiting conditions. However, the biochemical responses of the species under phosphorus (P) limiting conditions are still unknown. The growth and biochemical composition of Desmodesmus communis in response to different phosphorus concentrations were investigated in this research. Five different phosphorus conditions were used: control (BG11); excess treatments (50% P+, 75% P+) and limited treatments (50% P-, 75% P-The highest cell concentration was observed in 75% P+ (725.6 × 104 cells/mL), whereas the highest dry weight concentration (1.81 mg/L) was found in 50% P- medium. The highest total lipid (4.94%) accumulation was found in the 50% P + medium and the maximum protein (49.5%) content was detected in 50% P- medium. Fatty acid and amino acid compositions change according to P concentration. PUFAs concentrations are higher than SFAs and MUFAs. Therefore the microalgae biomass obtained from this study cannot be used for biodiesel production although it is more suitable for nutritional supplement productions.

The global explosion of eukaryotic algae: The potential role of phosphorus?

There arose one of the most important ecological transitions in Earth's history approximately 750 million years ago during the middle Neoproterozoic Era (1000 to 541 million years ago, Ma). Biomarker evidence suggests that around this time there was a rapid shift from a predominantly bacterial-dominated world to more complex ecosystems governed by eukaryotic primary productivity. The resulting 'Rise of the algae' led to dramatically altered food webs that were much more efficient in terms of nutrient and energy transfer. Yet, what triggered this ecological shift? In this study we examined the theory that it was the alleviation of phosphorus (P) deficiency that gave eukaryotic alga the prime opportunity to flourish. We performed laboratory experiments on the cyanobacterium Synechocystis salina and the eukaryotic algae Tetraselmis suecica and examined their ability to compete for phosphorus. Both these organisms co-occur in modern European coastal waters and are not known to have any allelopathic capabilities. The strains were cultured in mono and mixed cultures in chemostats across a range of dissolved inorganic phosphorus (DIP) concentrations to reflect modern and ancient oceanic conditions of 2 µM P and 0.2 µM P, respectively. Our results show that the cyanobacteria outcompete the algae at the low input (0.2 µM P) treatment, yet the eukaryotic algae were not completely excluded and remained a constant background component in the mixed-culture experiments. Also, despite their relatively large cell size, the algae T. suecica had a high affinity for DIP. With DIP input concentrations resembling modern-day levels (2 µM), the eukaryotic algae could effectively compete against the cyanobacteria in terms of total biomass production. These results suggest that the availability of phosphorus could have influenced the global expansion of eukaryotic algae. However, P limitation does not seem to explain the complete absence of eukaryotic algae in the biomarker record before ca. 750 Ma.

Isotope Composition of Nitrogen and Stoichiometric Ratios of Elements in Biomass of Spirogyra in Lake Baikal.

Using stable isotope analysis of nitrogen, for the first time the hypothesis on different sources of inorganic nutrients for two groups of littoral algae in Lake Baikal was confirmed. Strongly attached filamentous algae of genus Ulothrix, which developed in the wave-braking zone at depth 0.5 m, and loosely attached filamentous algae of genus Spirogyra, which developed in deeper layers 3.0-5.0 m in a low-turbulence zone, get inorganic nutrients presumably from surface discharge and groundwater inputs, respectively. Besides, stoichiometric ratios C:N and N:P in biomass of the algae indicated that growth of Spirogyra in Lake Baikal was likely limited by nitrogen, while growth of Ulothrix was limited by phosphorus.

Liquid Anaerobic Digestate as a Source of Nutrients for Lipid and Fatty Acid Accumulation by Auxenochlorella Protothecoides.

In recent years, there has been growing interest in the biomass of unicellular algae as a source of valuable metabolites. The main limitations in the commercial application of microbial biomass are associated with the costs of production thereof. Maize silage is one of the main substrates used in biogas plants in Europe. The effects of sterilized agricultural liquid digestate (LD) from methane fermentation of maize silage on the growth rates, macro and micronutrient removal efficiency, lipid content, and fatty acid profile in Auxenochlorella protothecoides were investigated. The results indicate that A. prothecoides can proliferate and accumulate lipids with simultaneous reduction of nutrients in the 1:20 diluted liquid digestate. The rate of nitrogen and phosphorus removal from the liquid digestate was 79.45% and 78.4%, respectively. Cells growing in diluted liquid digestate exhibited the maximum lipid content, i.e., 44.65%. The fatty acid profile of A. prothecoides shows a decrease in the content of linolenic acid by 20.87% and an increase in oleic acid by 32.16% in the LD, compared with the control. The liquid digestate changed the content of monounsaturated fatty acids and polyunsaturated fatty acids. The cells of A. protothecoides growing in the liquid digestate were characterized by lower PUFA content and higher MUFA levels.

Enhanced proliferation and differentiation of mesenchymal stem cells by astaxanthin-encapsulated polymeric micelles.

Astaxanthin is a highly potent antioxidant which can be extracted from Haematococcus pluvialis when cultivated and induced at high stress conditions. Due to astaxanthin's hydrophobicity, methoxypolyethylene glycol-polycaprolactone (mPEG-PCL) copolymer was synthesized to form polymeric micelles for the encapsulation of astaxanthin. Astaxanthin-loaded polymeric micelles were then used to examine the effects on the proliferation and differentiation of human mesenchymal stem cells (MSCs). Dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FT-IR) confirmed astaxanthin was encapsulated into mPEG-PCL micelles. Astaxanthin loading and encapsulation efficiency, determined by UV/Vis spectroscopy, were 3.27% and 96.67%, respectively. After 48 h, a total of 87.31% of astaxanthin was released from the polymeric micelles. The drug release profile was better fit by the Michaelis-Menten type model than the power law model. The MSC culture results showed that culture medium supplemented with 0.5 µg/mL astaxanthin-encapsulated polymeric micelles led to a 26.3% increase in MSC proliferation over an 8-day culture period. MSC differentiation results showed that 20 ng/mL astaxanthin-encapsulated polymeric micelles enhanced adipogenesis, chondrogenesis, and osteogenesis of MSCs by 52%, 106%, and 182%, respectively.

'Red - the magic color for solar salt production' - but since when?

Dense communities of carotenoid-rich members of the Halobacteria (Euryarchaeota), the bacterium Salinibacter (Bacteroidetes) and the eukaryotic alga Dunaliella color the brines of most saltern crystallizer ponds red. The first report we found from the western world mentioning these red brines dates from 1765: the Encyclopédie of Diderot and coworkers. Earlier descriptions of solar salterns since Roman times do not mention red ponds. These include the Astronomica of Manilius, Pliny's Naturalis Historia (1st century), the description of Italian salterns in De Reditu Suo by Namatianus (5th century), Agricola's De Re Metallica (1556) and an anonymous description of French salterns (1669). This suggests that in earlier times, saltern brines may not have been red. In salterns which are operated today in the traditional way as practiced in the Middle Ages, no red brines are observed. Prokaryotic densities in the salterns of Secovlje (Slovenia) and Ston (Croatia) are an order of magnitude lower than in modern saltern crystallizers. This is probably due to the much shorter residence time of the brine in the traditionally operated salterns. In China, red saltern brines were documented earlier: in Li Shizhen's compendium of Materia Medica Ben Cao Kang Mu, completed in 1578 and based on older sources.

Nutrient removal in an algal membrane photobioreactor: effects of wastewater composition and light/dark cycle.

Graesiella emersonii was cultivated in an osmotic membrane photobioreactor (OMPBR) for nutrients removal from synthetic wastewater in continuous mode. At 1.5 days of hydraulic retention time and under continuous illumination, the microalgae removed nitrogen (N) completely at influent NH4+-N concentrations of 4-16 mg/L, with removal rates of 3.03-12.1 mg/L-day. Phosphorus (P) removal in the OMPBR was through biological assimilation as well as membrane rejection, but PO43--P assimilation by microalgae could be improved at higher NH4+-N concentrations. Microalgae biomass composition was affected by N/P ratio in wastewater, and a higher N/P ratio resulted in higher P accumulation in the biomass. The OMPBR accumulated about 0.35 g/L biomass after 12 days of operation under continuous illumination. However, OMPBR operation under 12 h light/12 h dark cycle lowered biomass productivity by 60%, which resulted in 20% decrease in NH4+-N removal and nearly threefold increase in PO43--P accumulation in the OMPBR. Prolonged dark phase also affected carbohydrate accumulation in biomass, although its effects on lipid and protein accumulation were negligible. The microalgae also exhibited high tendency to aggregate and settle, which could be attributed to reduction in cell surface charge and enrichment of soluble algal products in the OMPBR. Due to a relatively shorter operating period, membrane biofouling and salt accumulation did not influence the permeate flux significantly. These results improve the understanding of the effects of N/P ratio and light/dark cycle on biomass accumulation and nutrients removal in the OMPBR.

Growth and Nutrient Utilization of Green Algae in Batch and Semicontinuous Autotrophic Cultivation Under High CO2 Concentration.

The growth performance of Chlorella protothecoides, Chlorella pyrenoidosa, and Chlorella sp. in autotrophic cultivation with 10% carbon dioxide (CO2) was evaluated. The biomass production of C. protothecoides, along with its carbon, nitrogen (N), and phosphorus (P) utilization, in batch and semicontinuous autotrophic cultivation with 20% CO2 was also determined. Among the three algae species, C. protothecoides obtained the highest biomass yield (1.08 g/L) and P assimilation (99.4%). Compared with the CO2 flow rate and inoculation ratio in batch cultivation, light intensity considerably improved biomass yield, N and P assimilation, and CO2 utilization. In the semicontinuous cultivation of C. protothecoides, a hydraulic retention time (HRT) of 8 days kept the system at a stable running state, thereby demonstrating that an HRT of 8 days was better than an HRT of 5 days. Among the three N/P ratios for C. protothecoides in semicontinuous cultivation with 20% CO2, 2:1 provided the highest biomass productivity (0.19 g/L/day) and CO2 fixation rate (0.37 g/L/day). Therefore, this lower N/P ratio is more suitable than 10:1 and 50:1 for the growth of C. protothecoides with 20% CO2. Compared with the batch cultivation of C. protothecoides, semicontinuous cultivation improved the CO2 fixation rate (by 1.5-2 times) and CO2 utilization efficiency (by 3-6 times) of C. protothecoides.

Responses of freshwater algal cell density to hydrochemical variables in an urban aquatic ecosystem, northern China.

In this paper, the algal cell density of cyanobacteria, green algae, and diatoms and their responses to the hydrochemical factors were analyzed to reveal the structural characteristics of water quality in an urban river. A total of nine sampling sites from upstream to downstream was explored in our study. At each site, the density of algae was identified every week during the wet season (June-October) from 2012 to 2017, and in situ detection was used for the relative 11 hydrochemical variables. The temporal and spatial characteristics of 14 variables were analyzed using a heatmap coupled with the cluster analysis method. The trend of each parameter was analyzed using the smoothing method with locally weighted regression. The nonmetric multidimensional scaling method was employed to detect the temporal and spatial similarities among algae along hydrochemical gradients. The responses of algal density to hydrochemical variables were analyzed using a redundancy analysis. The results showed that the water temperature (Wtemp), pH, dissolved oxygen (DO), cyanobacteria, and diatoms exhibited significant declining trends, and significant increasing trends were shown in the permanganate index, chemical oxygen demand, total nitrogen, ammonia nitrogen, and total phosphorus; the cyanobacteria exhibited certain differences with green algae and diatoms in summer and the downstream areas of the river. The temporal-spatial homogeneity of algal to hydrochemical variables showed the key influencing factors of Wtemp for cyanobacteria density, chlorophyll for green algae density, DO, and pH for diatoms. The results presented here are valuable for deepening our understanding of river ecosystem evaluations and effective environmental management, as well as an important reference for the sustainable development of aquatic biological resources.

Aquaculture biological waste as culture medium to cultivation of Ankistrodesmus gracilis (Reinsch) Korshikov / Resíduos biológicos de aquicultura como meio de cultura para o cultivo de Ankistrodesmus gracilis (Reinsch) Korshikov

Abstract Current study investigated the effectiveness of different macrophytes as culture media for Ankistrodesmus gracilis in laboratory conditions. Significant difference (p < 0.05) was reported in cell density with regard to conventional culture medium (CHU12) and macrophytes culture media. Mean cell density in NPK, Eichhornia crassipes and E. azurea media was higher (p < 0.05) than in conventional culture medium. Chlorophyll-a was higher than 1 g.L-1, except in CHU12 (0.7 ± 0.4 g.L-1) and T. domingensis (0.8 ± 0.3 g.L-1) media. Nitrate decreased sharply as from the 7th-day of the experiment. Ammonium and total phosphorus were highest in culture media and ranged between 0.4 g.L-1 (P. cordata medium) and 1.7 g.L-1 (CHU12 medium) for ammonium, and between 0.8 g.L-1 (CHU12 medium) and 1.9 g.L-1 (T. domingensis medium) for total phosphorus. Results revealed inorganic fertilizer and macrophytes combined with vitamins may be effective as culture media and strongly supports the growth of Ankistrodesmus gracilis, since cell density and biochemical composition are similar to or higher than conventional culture medium (CHU12). Macrophyte is a tool for aquaculture since biological wastes may be used with nutrients to improve the cultivation of microalgae.

Resumo O presente estudo investigou a eficácia na utilização de diferentes macrófitas como meio de cultura para Ankistrodesmus gracilis em condições laboratoriais. Foi observada diferença significativa (p < 0,05) entre a densidade celular em relação aos meios de cultura convencional (CHU12) e de macrófitas. Os meios de cultura com Eichhornia crassipes, E. azurea e NPK apresentaram densidade celular maiores (p < 0,05) que o meio de cultura convencional. Os teores de clorofila-a foram superiores a 1 g.L-1, exceto nos meios de cultura CHU12 (0.7 ± 0.4 g.L-1) e de T. domingensis (0.7 ± 0.3 g.L-1). O nitrato diminuiu acentuadamente a partir do 7º dia de experimento. Dentre os nutrientes, amônia e o fósforo total foram os mais elevados nos meios de cultura, variando entre 0.4 g.L-1 (meio de P. cordata) a 1,7 g.L-1 (meio CHU12) para amônia e, entre 0.8 g.L-1 (meio CHU12) e 1,9 gL-1 (meio de T. domingensis) para o fósforo total. Os resultados do presente estudo mostraram que o uso de fertilizantes inorgânicos e macrófitas, combinados com vitaminas, pode ser eficaz como meio de cultura no crescimento de Ankistrodesmus gracilis, uma vez que a densidade celular e a composição bioquímica foram semelhantes ou superiores ao meio de cultura convencional (CHU12). As macrófitas são ferramentas a serem adotadas na aquicultura, desde que os resíduos biológicos podem ser usados como nutrientes para melhorar o cultivo de microalgas.

Microalgae population dynamics growth with AnMBR effluent: effect of light and phosphorus concentration.

The aim of this study was to evaluate the effect of light intensity and phosphorus concentration on biomass growth and nutrient removal in a microalgae culture and their effect on their competition. The photobioreactor was continuously fed with the effluent from an anaerobic membrane bioreactor pilot plant treating real wastewater. Four experimental periods were carried out at different light intensities (36 and 52 µmol s-1 m-2) and phosphorus concentrations (around 6 and 15 mgP L-1). Four green algae - Scenedesmus, Chlorella, Monoraphidium and Chlamydomonas- and cyanobacterium were detected and quantified along whole experimental period. Chlorella was the dominant species when light intensity was at the lower level tested, and was competitively displaced by a mixed culture of Scenedesmus and Monoraphidium when light was increased. When phosphorus concentration in the photobioreactor was raised up to 15 mgP L-1, a growth of cyanobacterium became the dominant species in the culture. The highest nutrient removal efficiency (around 58.4 ± 15.8% and 96.1 ± 16.5% of nitrogen and phosphorus, respectively) was achieved at 52 µmol s-1 m-2 of light intensity and 6.02 mgP L-1 of phosphorus concentration, reaching about 674 ± 86 mg L-1 of volatile suspended solids. The results obtained reveal how the light intensity supplied and the phosphorus concentration available are relevant operational factors that determine the microalgae species that is able to predominate in a culture. Moreover, changes in microalgae predominance can be induced by changes in the growth medium produced by the own predominant species.

Phosphorus and metal removal combined with lipid production by the green microalga Desmodesmus sp.: An integrated approach.

This work focused on the potential of Desmodesmus sp. to be employed for wastewater bioremediation and biodiesel production. The green microalga was grown in a culture medium with a phosphorus (P) content of 4.55 mg L-1 simulating an industrial effluent; it was also exposed to a bimetal solution of copper (Cu) and nickel (Ni) for 2 days. P removal was between 94 and 100%. After 2 days of exposure to metals, 94% of Cu and 85% of Ni were removed by Desmodesmus sp. Adsorption tests showed that the green microalga was able to remove up to 90% of Cu and 43% of Ni in less than 30 min. The presence of metals decreased the lipid yield, but biodiesel quality from the biomass obtained from metal exposed samples was higher than that grown without metals. This result revealed that this technology could offer a new alternative solution to environmental pollution and carbon-neutral fuel generation.

The enhanced biomass and lipid accumulation in Coccomyxa subellipsoidea with an integrated treatment strategy initiated by brewery effluent and phytohormones.

Brewery effluent (BE) as an appreciable and sustainable resource presented new possibilities in low-cost algal biomass production, whereas the relatively low essential macronutrients hindered extensive applications as growth medium for microalgae cultivation. The objective of this study was to investigate the feasibility of an integrated treatment strategy initiated by BE coupling phytohormones in augmenting biomass and lipid accumulation in Coccomyxa subellipsoidea. Results revealed that BE coupling synthetic 1-naphthaleneacetic acid (NAA) accomplished the favorable lipid productivity of 481.76 mg/L/days, representing 6.80- to 9.71-fold more than that of single BE as well as standard Basal media. BE coupling NAA feeding also heightened the proportions of C16-C18 fatty acids (over 96%) and mono-unsaturated C18:1 (approximate 45%) which were prone to high-quality biofuels-making. Such profound lipids accumulation might be attributable to that BE coupling NAA treatment drove most of metabolic flux (i.e. acetyl-CoA) derived from TCA cycle and glycolysis flowing into lipid accumulation pathway. Concurrently, the complete removal of total nitrogen and total phosphorus by C. subellipsoidea with assistance of NAA were easily complied with the permissible dischargeable limits for BE. These present results strongly demonstrated that BE coupling NAA was a potential feeding strategy in boosting algal lipid productivity and further provided great possibilities in linking affordable algal biomass production with high-efficient biological contaminants removal.

Production of lutein, and polyunsaturated fatty acids by the acidophilic eukaryotic microalga Coccomyxa onubensis under abiotic stress by salt or ultraviolet light.

In this study, the effect of abiotic stress on the acidophilic eukaryotic microalga, Coccomyxa onubensis, was analyzed for the production of lutein and PUFAs (polyunsaturated fatty acids). It grows autotrophically at a pH of 2.5. It showed a growth rate of 0.30 d-1, and produced approximately 122.50 mg·L-1·d-1 biomass, containing lipids (300.39 mg g-1dw), lutein (5.30 mg g-1dw), and ß-carotene (1.20 mg g-1dw). The fatty acid methyl ester (FAME) fraction was 89.70 mg g-1dw with abundant palmitic acid (28.70%) and linoleic acid (37.80%). The addition of 100 mM NaCl improved the growth rate (0.54 d-1), biomass productivity (243.75 mg·L-1·d-1), and lipids accumulation (416.16 mg g-1dw). The microalga showed a lutein content of 6.70 mg g-1dw and FAME fraction of 118.90 mg g-1dw; 68% of the FAMEs were PUFAs. However, when 200-500 mM salt was added, its growth was inhibited but there was a significant induction of lutein (up to 7.80 mg g-1dw). Under continuous illumination with PAR (photosynthetically active radiations) +UVA (ultraviolet A, 8.7 W m-2), C. onubensis showed a growth rate of 0.40 d-1, and produced 226.3 mg·L-1·d-1 biomass, containing lipids, (487.26 mg g-1dw), lutein (7.07 mg g-1dw), and FAMEs (232.9 mg g-1dw); 48.4% of the FAME were PUFAs. The illumination with PAR + UVB (ultraviolet B, 0.16 W m-2) was toxic for cells. These results indicate that C. onubensis biomass is suitable as a supplement for functional foods and/or source of high added value products.

Surface-flow constructed wetlands dominated by Cladophora for reclaiming nutrients in diffuse domestic effluent.

In this work, a surface-flow constructed wetland (SFCW) dominated by Cladophora was used to remove and reclaim nutrients in diffuse domestic effluent (DDE) discharged from rural regions around Taihu Lake, a eutrophic shallow lake in China. Growth rate of Cladophora was investigated and linked to ambient factors and nutrient consuming rates. The growth performances of Cladophora and animal-feed microbes were studied during the commissioning of SFCW. Results show that the growth rate of Cladophora was closely correlated with field temperature and surface irradiance, while surface coverage was suitable for the manipulation of SFCW. Harvest of Cladophora along with animal-feed microbes and removal of nutrients in DDE could be achieved by manipulating surface coverage to drag growth rate back at the end of linear zone and to quickly restore Cladophora biomass in the mid zone of surface growth rate. Among four stages of the commissioning, concentrating stage experienced the majority species of animal-feed microbes and maximal nutrient removal; during decomposing stage, however, the reproduction of animal-feed microbes and nutrient removal were lower, whereas the density of pathogens was higher.

Aquaculture biological waste as culture medium to cultivation of Ankistrodesmus gracilis (Reinsch) Korshikov.

Current study investigated the effectiveness of different macrophytes as culture media for Ankistrodesmus gracilis in laboratory conditions. Significant difference (p < 0.05) was reported in cell density with regard to conventional culture medium (CHU12) and macrophytes culture media. Mean cell density in NPK, Eichhornia crassipes and E. azurea media was higher (p < 0.05) than in conventional culture medium. Chlorophyll-a was higher than 1 g.L-1, except in CHU12 (0.7 ± 0.4 g.L-1) and T. domingensis (0.8 ± 0.3 g.L-1) media. Nitrate decreased sharply as from the 7th-day of the experiment. Ammonium and total phosphorus were highest in culture media and ranged between 0.4 g.L-1 (P. cordata medium) and 1.7 g.L-1 (CHU12 medium) for ammonium, and between 0.8 g.L-1 (CHU12 medium) and 1.9 g.L-1 (T. domingensis medium) for total phosphorus. Results revealed inorganic fertilizer and macrophytes combined with vitamins may be effective as culture media and strongly supports the growth of Ankistrodesmus gracilis, since cell density and biochemical composition are similar to or higher than conventional culture medium (CHU12). Macrophyte is a tool for aquaculture since biological wastes may be used with nutrients to improve the cultivation of microalgae.

Nutritional and bioactive compounds of commercialized algae powders used as food supplements.

The main nutritional/bioactive compounds (protein; aminoacids, AA; fucose; minerals; vitamins B12 and C; and total phenolic content, TPC) of nine commercial algae powders, used as food supplements, were studied. Undaria pinnatifida showed the highest protein/aminoacid contents (51.6/54.4 g 100 g-1). Among brown macroalgae, Himanthalia elongata showed the highest fucose content (26.3 g kg-1) followed by Laminaria ochroleuca (22.5 g kg-1). Mineral contents of 15-24% were observed in the algae, being particularly excellent sources of iodine (69.0-472.0 mg kg-1). Porphyra spp. and Palmaria palmata showed the highest vitamin B12 contents (667-674 µg kg-1). Vitamin C ranged among 490.4-711.8 mg kg-1. H. elongata showed the highest total phenolic content (14.0 g kg-1). In conclusion, the studied algae are excellent sources of protein, AA, minerals, vitamin C and some of them presented particularly high vitamin B12 and fucose contents, which may have a potential use as food supplements.

Quantitative proteomics of a B12 -dependent alga grown in coculture with bacteria reveals metabolic tradeoffs required for mutualism.

The unicellular green alga Lobomonas rostrata requires an external supply of vitamin B12 (cobalamin) for growth, which it can obtain in stable laboratory cultures from the soil bacterium Mesorhizobium loti in exchange for photosynthate. We investigated changes in protein expression in the alga that allow it to engage in this mutualism. We used quantitative isobaric tagging (iTRAQ) proteomics to determine the L. rostrata proteome grown axenically with B12 supplementation or in coculture with M. loti. Data are available via ProteomeXchange (PXD005046). Using the related Chlamydomonas reinhardtii as a reference genome, 588 algal proteins could be identified. Enzymes of amino acid biosynthesis were higher in coculture than in axenic culture, and this was reflected in increased amounts of total cellular protein and several free amino acids. A number of heat shock proteins were also elevated. Conversely, photosynthetic proteins and those of chloroplast protein synthesis were significantly lower in L. rostrata cells in coculture. These observations were confirmed by measurement of electron transfer rates in cells grown under the two conditions. The results indicate that, despite the stability of the mutualism, L. rostrata experiences stress in coculture with M. loti, and must adjust its metabolism accordingly.

Pressurized liquid extraction of Neochloris oleoabundans for the recovery of bioactive carotenoids with anti-proliferative activity against human colon cancer cells.

In recent years, the green microalgae Neochloris oleoabundans have demonstrated to be an interesting natural source of carotenoids that could be used as potential food additive. In this work, different N. oleoabundans extracts obtained by pressurized liquid extraction (PLE) have been analyzed in depth to evaluate the influence of different culture conditions (effect of nitrogen, light intensity or carbon supplied) not only on the total carotenoid content but also on the carotenoid composition produced by these microalgae. Regardless of the cultivation conditions, lutein and carotenoid monoesters were the most abundant carotenoids representing more than 60% of the total content in all extracts. Afterwards, the effect of the different N. oleoabundans extracts and the dose-effect of the most potent algae extracts (namely, N9, PS and CO2 (-)) on the proliferation of human colon cancer cells lines (HT-29 and SW480) and a cell line established from a primary colon cancer cell culture (HGUE-C-1) were evaluated by an MTT assay whereas a stepwise multiple regression analysis was performed to get additional evidences on the relationship between carotenoid content and the antiproliferative activity. Results revealed that, as a general trend, those extracts with high total carotenoid content showed comparably antiproliferative activity being possible to establish a high correlation between the cell proliferation values and the carotenoid constituents. Monoesters showed the highest contribution to cell proliferation inhibition whereas lutein and violaxanthin showed negative correlation and diesters and zeaxanthin showed a positive significant contribution to cell proliferation.

Effects of Salt Concentrations and Nitrogen and Phosphorus Starvations on Neutral Lipid Contents in the Green Microalga Dunaliella tertiolecta.

Dunaliella tertiolecta, a halotolerant alga, can accumulate large amounts of neutral lipid, which makes it a potential biodiesel feedstock. In this study, neutral lipids of D. tertiolecta induced by different salinities or N or P starvation were analyzed by thin-layer chromatography (TLC), flow cytometry (FCM), and confocal laser scanning microscopy (CLSM). High salinities or N or P starvation resulted in a decrease in cell growth and chlorophyll contents of D. tertiolecta. Neutral lipid contents increased markedly after 3-7 days of N starvation or at low NaCl concentrations (0.5-2.0 M). N starvation had a more dramatic effect on the neutral lipid contents of D. tertiolecta than P starvation. Four putative ME isozymes in different conditions can be detected by using isozyme electrophoresis. Two alternative acetyl-CoA producers, ACL and ACS genes, were up-regulated under low salinities and N starvation. It was suggested that low salinities and N starvation are considered efficient ways to stimulate lipid accumulation in D. tertiolecta.