Long-term cyclic persistence in an experimental predator-prey system.

Predator-prey cycles rank among the most fundamental concepts in ecology, are predicted by the simplest ecological models and enable, theoretically, the indefinite persistence of predator and prey1-4. However, it remains an open question for how long cyclic dynamics can be self-sustained in real communities. Field observations have been restricted to a few cycle periods5-8 and experimental studies indicate that oscillations may be short-lived without external stabilizing factors9-19. Here we performed microcosm experiments with a planktonic predator-prey system and repeatedly observed oscillatory time series of unprecedented length that persisted for up to around 50 cycles or approximately 300 predator generations. The dominant type of dynamics was characterized by regular, coherent oscillations with a nearly constant predator-prey phase difference. Despite constant experimental conditions, we also observed shorter episodes of irregular, non-coherent oscillations without any significant phase relationship. However, the predator-prey system showed a strong tendency to return to the dominant dynamical regime with a defined phase relationship. A mathematical model suggests that stochasticity is probably responsible for the reversible shift from coherent to non-coherent oscillations, a notion that was supported by experiments with external forcing by pulsed nutrient supply. Our findings empirically demonstrate the potential for infinite persistence of predator and prey populations in a cyclic dynamic regime that shows resilience in the presence of stochastic events.

Microalgae biofilm formation and antioxidant responses to stress induce by Lemna minor L., Chlorella vulgaris, and Aphanizomenon flos-aquae.

The study shows how microalgae biofilm formation and antioxidant responses to the production of reactive oxygen species (ROS) is alter by the presences of Lemna minor L., Chlorella vulgaris, and Aphanizomenon flos-aquae. The study involves the cultivation of the biofilm of Chlorella vulgaris and Aphanizomenon flos-aquae in three bioreactors. The condition of growth for the biofilm formation was varied across the three bioreactors to enable the dominance Chlorella vulgaris and Aphanizomenon flos-aquae in one of the bioreactors. Lemna minor L. was also introduce into one of the bioreactors to determine its effect on the biofilm formation. The result obtained shows that C. vulgaris and A. flos-aquae dominate the biofilm, resulting in a high level of H2O2 and O2- (H2O2 was 0.122 ± 0.052 and 0.183 ± 0.108 mmol/L in C. vulgaris and A. flos-aquae, respectively, and O2- was 0.261 ± 0.039 and 0.251 ± 0.148 mmol/L in C. vulgaris and A. flos-aquae, respectively). The study also revealed that the presence of L. minor L. tend to reduce the oxidative stress to the biofilm leading to low production of ROS (H2O2 was 0.086 ± 0.027 and 0.089 ± 0.045 mmol/L in C. vulgaris and A. flos-aquae respectively, and O2- was 0.185 ± 0.044 and 0.161 ± 0.065 mmol/L in C. vulgaris and A. flos-aquae respectively). The variation in the ability of the biofilm of C. vulgaris and A. flos-aquae to respond via chlorophyll, carotenoid, flavonoid, anthocyanin, superoxide dismutase, peroxidase, catalase, glutathione reductase activities, antioxidant reducing power, phosphomolybdate activity, DPPH reduction activity, H2O2 scavenging activity, lipid content and organic carbon also supports the fact that the presence of biomass of microalgae and aquatic macrophytes tend to affect the process of microalgae biofilm formation and the ability of the biofilm to produce antioxidant. This high nutrient utilization leads to the production of biomass which can be used for biofuel production and other biotechnological products.

Effects of Sulfamethoxazole Exposure on the Growth, Antioxidant System of Chlorella vulgaris and Microcystis aeruginosa.

Sulfamethoxazole (SMZ) is a kind of sulfonamides antibiotic, which is widely used in human life. This study investigated the effects of SMZ on physiological and biochemical indexes of Chlorella vulgaris (C. vulgaris) and Microcystis aeruginosa (M. aeruginosa) for 35-day. The results showed that SMZ inhibited the growth and Chl-a content of C. vulgaris and M. aeruginosa, and growth inhibition rate was 8.06%-95.86%, Chl-a content decreased 2.44%-98.04%. SMZ resulting in increased SOD and CAT activity and destroyed the dynamic balance of antioxidant system. In addition, SMZ increased the content of malondialdehyde (MDA) in algae, destroyed the cell membrane to a certain extent, which was 1.8-7.3 folds higher than the control group. High concentration of SMZ can make algae cells exceed the limit of cell antioxidant capacity. Coupled with the serious damage of cell membrane, algae cells begin to appear a large number of death phenomenon.

Chlorella vulgaris integrates photoperiod and chloroplast redox signals in response to growth at high light.

MAIN CONCLUSION: Photoacclimation to variable light and photoperiod regimes in C. vulgaris represents a complex interplay between "biogenic" phytochrome-mediated sensing and "operational" redox sensing signaling pathways. Chlorella vulgaris Beijerinck UTEX 265 exhibits a yellow-green phenotype when grown under high light (HL) in contrast to a dark green phenotype when grown at low light (LL). The redox state of the photosynthetic electron transport chain (PETC) as estimated by excitation pressure has been proposed to govern this phenotypic response. We hypothesized that if the redox state of the PETC was the sole regulator of the HL phenotype, C. vulgaris should photoacclimate in response to the steady-state excitation pressure during the light period regardless of the length of the photoperiod. As expected, LL-grown cells exhibited a dark green phenotype, low excitation pressure (1 - qP = 0.22 ± 0.02), high chlorophyll (Chl) content (375 ± 77 fg Chl/cell), low Chl a/b ratio (2.97 ± 0.18) as well as high photosynthetic efficiency and photosynthetic capacity regardless of the photoperiod. In contrast, C. vulgaris grown under continuous HL developed a yellow-green phenotype characterized by high excitation pressure (1 - qP = 0.68 ± 0.01), a relatively low Chl content (180 ± 53 fg Chl/cell), high Chl a/b ratio (6.36 ± 0.54) with concomitantly reduced light-harvesting polypeptide abundance, as well as low photosynthetic capacity and efficiency measured on a per cell basis. Although cells grown under HL and an 18 h photoperiod developed a typical yellow-green phenotype, cells grown at HL but a 12 h photoperiod exhibited a dark green phenotype comparable to LL-grown cells despite exhibiting growth under high excitation pressure (1 - qP = 0.80 ± 0.04). The apparent uncoupling of excitation pressure and phenotype in HL-grown cells and a 12 h photoperiod indicates that chloroplast redox status cannot be the sole regulator of photoacclimation in C. vulgaris. We conclude that photoacclimation in C. vulgaris to HL is dependent upon growth history and reflects a complex interaction of endogenous systems that sense changes in photoperiod as well as photosynthetic redox balance.

Effect of algae acclimation to the wastewater medium on the growth kinetics and nutrient removal capacity.

Algal treatment methods have been widely used in nutrient removal studies. However, in most cases, the experimental conditions have not been fully complied with actual conditions. For instance, the effect of algae acclimation to wastewater medium on cell growth and removal efficiency has generally been ignored in laboratory scale experiments. This paper investigates the effect of acclimation on cell growth and nutrient uptake rates of Arthrospira platensis and Chlorella vulgaris. For this purpose, batch reactors, which contained the synthetic secondary effluent, had been inoculated by acclimated algae cells and the growth parameters were measured daily, as well as nutrient concentration. A significant decrease (P < 0.05) in chlorophyll-a content of acclimated A. platensis was observed, although there was no significant change in specific growth rate (µ) and doubling time (dt), in comparison with the non-acclimated ones. Moreover, the acclimation process changed the chlorophyll-a content and kinetic parameters of Chlorella vulgaris. Furthermore, t test results showed a significant increase in removal rate of nitrogen compounds through the acclimation. Residence time of A. platensis and C. vulgaris was also reduced through the acclimation by approximately 50% and 25%, respectively.

Physiological and enzymatic responses of Chlorella vulgaris exposed to produced water and its potential for bioremediation.

In South America, Colombia is known as an important oil-producing country. However, the environmental impact of crude oil industry has not been studied deeply and few studies have been carried out for evaluating responses of algae and its adaptation under specific conditions. Enzymatic and physiological effects in Chlorella vulgaris and its potential for bioremediation after exposure to produced water (PW) were assessed using different PW concentrations (0, 25, 50, 75 and 100%) and crude oil. Variables such as cell density, growth rate (µ), percentage of growth inhibition (% I), chlorophyll a and b and cell diameter were evaluated during 5 days. Furthermore, enzymatic biomarkers such as superoxide dismutase (SOD) and catalase (CAT) were also measured. Results showed that the treatment with 100% PW had the highest cell density and µ; similarly, 25% PW treatment had a similar behaviour, being these two treatments with the highest growth. A dose-dependent response was seen for chlorophyll a and b and cell diameter, showing significant differences between treatments and the control. Different levels of SOD and CAT were observed in algae exposed to PW. At 24 h, an increase in SOD and CAT activity was observed, probably due to effects caused by xenobiotics. After 72 h, a decrease in the activity of both enzymes was observed. The results evidenced that C. vulgaris can adapt easily to PW, showing an increase on its growth and stabilisation in its antioxidant activity. Additionally, cell diameter results and decrease of hydrocarbons and phenols show the potential of these algae to degrade xenobiotics from PW.

Toxic Effects of Selected Textile Dyes on Elemental Composition, Photosynthetic Pigments, Protein Content and Growth of a Freshwater Chlorophycean Alga Chlorella vulgaris.

Toxicity of three textile dyes-Optilan yellow, Drimarene blue and Lanasyn brown, was evaluated in a green alga Chlorella vulgaris. The unialgal populations of the alga showed a concentration-dependent decrease in specific growth rate and pigments after exposure to graded concentrations of above dyes. The elemental profile (C, H, N, S) of the treated and untreated cells showed a change which was evident from a significant decrease in the quantity of elements after exposure to the dyes. The observations provide convincing evidence that the textile dyes inhibited the growth, pigment and elemental composition of the algal cells. The findings of the present investigation will contribute to gaining a better understanding of the impacts of textile dyes on ecologically important aquatic organisms.

A comprehensive comparable study of the physiological properties of four microalgal species under different light wavelength conditions.

MAIN CONCLUSION: Microalgae treated with blue light have potential for production of human nutrition supplement and biofuel due to their higher biomass productivity and favorable fatty acid composition. Chlorella vulgaris, Chlorella pyrenoidosa, Scenedesmus quadricauda and Scenedesmus obliquus are representative green microalgae which are widely reported for algal production. In this study, we provide a systematic investigation of the biomass productivity, photosynthetic pigments, chlorophyll fluorescence and fatty acid content of the four green microalgae. The strains were grown in two primary monochromatic light wavelengths [red and blue LEDs (light emitting diode)], and in white LED conditions, respectively. Among them, blue LED light was determined as the best light for growth rate, followed by red LED and white LED. The chlorophyll generation was more sensitive to the monochromatic blue light. The polyunsaturated fatty acids (PUFAs) such as α-linolenic acid (18:3), which were perfect for human nutrition supplementation, showed high concentrations in these algae strains under blue LED. Collectively, the results indicate that the blue LED is suitable for various food, feed, and algal biofuel productions due to both biomass and fatty acid productivity.

Impact of Nutrient Availability on Tertiary Wastewater Treatment by Chlorella vulgaris.

Algae can use excessive nutrients from wastewater effluent to generate beneficial products such as biofuels. However, fluctuation of wastewater characteristics could hinder the implementation of tertiary algal treatment. This study aims to identify the impact of nutrient availability on Chlorella vulgaris's ability to remove nitrogen and phosphorus from wastewater, and its potential as a biofuel feedstock. Experiments using synthetic wastewater with varying concentrations of nitrate and phosphate showed C. vulgaris continued to remove either nutrient when the other was exhausted. Nitrogen starvation led the algae to accumulate the highest amount of neutral lipid; however, the exhaustion of phosphorus did not produce such impact. Synergistic effect was also observed between C. vulgaris and indigenous microorganisms in nutrient removal from real wastewater effluent. The results showed C. vulgaris can survive in a range of nutrient-limiting conditions, making tertiary algal treatment applicable following various secondary treatment regimes.

Formation of water disinfection byproduct 2,6-dichloro-1,4-benzoquinone from chlorination of green algae.

We report that green algae in lakes and rivers can serve as precursors of halobenzoquinone (HBQ) disinfection byproducts (DBPs) produced during chlorination. Chlorination of a common green alga, Chlorella vulgaris, produced 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), the most prevalent HBQ DBP in disinfected water. Under varying pH conditions (pH6.0-9.0), 2,6-DCBQ formation ranged from 0.3 to 2.1µg/mg C with maximum formation at pH8.0. To evaluate the contribution of organic components of C. vulgaris to 2,6-DCBQ formation, we separated the organics into two fractions, the protein-rich fraction of intracellular organic matter (IOM) and the polysaccharide-laden fraction of extracellular organic matter (EOM). Chlorination of IOM and EOM produced 1.4µg/mg C and 0.7µg/mg C of 2,6-DCBQ, respectively. The IOM generated a two-fold higher 2,6-DCBQ formation potential than the EOM fraction, suggesting that proteins are potent 2,6-DCBQ precursors. This was confirmed by the chlorination of proteins extracted from C. vulgaris: the amount of 2,6-DCBQ produced is linearly correlated with the concentration of total algal protein (R2=0.98). These results support that proteins are the primary precursors of 2,6-DCBQ in algae, and control of green algal bloom outbreaks in source waters is important for management of HBQ DBPs.

Pterodon emarginatus oleoresin-based nanoemulsion as a promising tool for Culex quinquefasciatus (Diptera: Culicidae) control.

BACKGROUND: Preparation of nanoformulations using natural products as bioactive substances is considered very promising for innovative larvicidal agents. On this context, oil in water nanoemulsions develop a main role, since they satisfactorily disperse poor-water soluble substances, such as herbal oils, in aqueous media. Pterodon emarginatus, popularly known as sucupira, has a promising bioactive oleoresin. However, to our knowledge, no previous studies were carried out to evaluate its potential against Culex quinquefasciatus, the main vector of the tropical neglected disease called lymphatic filariasis or elephantiasis. Thus, we aimed to investigate influence of different pairs of surfactants in nanoemulsion formation and investigate if a sucupira oleoresin-based nanoemulsion has promising larvicidal activity against this C. quinquefasciatus. We also evaluated morphological alteration, possible mechanism of insecticidal action and ecotoxicity of the nanoemulsion against a non-target organism. RESULTS: Among the different pairs of surfactants that were tested, nanoemulsions obtained with polysorbate 80/sorbitan monooleate and polysorbate 80/sorbitan trioleate presented smallest mean droplet size just afterwards preparation, respectively 151.0 ± 2.252 and 160.7 ± 1.493 nm. They presented high negative zeta potential values, low polydispersity index (<0.300) and did not present great alteration in mean droplet size and polydispersity index after 1 day of preparation. Overall, nanoemulsion prepared with polysorbate 80/sorbitan monooleate was considered more stable and was chosen for biological assays. It presented low LC50 value against larvae (34.75; 7.31-51.86 mg/L) after 48 h of treatment and some morphological alteration was observed. The nanoemulsion did not inhibit acetylcholinesterase of C. quinquefasciatus larvae. It was not toxic to green algae Chlorella vulgaris at low concentration (25 mg/L). CONCLUSIONS: Our results suggest that optimal nanoemulsions may be prepared with different surfactants using a low cost and low energy simple method. Moreover, this prototype proved to be effective against C. quinquefasciatus, being considered an ecofriendly novel nanoproduct that can be useful in integrated control programs of vector control.

Volatile organic compounds released from Microcystis flos-aquae under nitrogen sources and their toxic effects on Chlorella vulgaris.

Eutrophication promotes massive growth of cyanobacteria and algal blooms, which can poison other algae and reduce biodiversity. To investigate the differences in multiple nitrogen (N) sources in eutrophicated water on the emission of volatile organic compounds (VOCs) from cyanobacteria, and their toxic effects on other algal growth, we analyzed VOCs emitted from Microcystis flos-aquae with different types and concentrations of nitrogen, and determined the effects under Normal-N and Non-N conditions on Chlorella vulgaris. M. flos-aquae released 27, 22, 20, 27, 19, 25 and 17 compounds, respectively, with NaNO3, NaNO2, NH4Cl, urea, Ser, Lys and Arg as the sole N source. With the reduction in N amount, the emission of VOCs was increased markedly, and the most VOCs were found under Non-N condition. C. vulgaris cell propagation, photosynthetic pigment and Fv/Fm declined significantly following exposure to M. flos-aquae VOCs under Non-N condition, but not under Normal-N condition. When C. vulgaris cells were treated with two terpenoids, eucalyptol and limonene, the inhibitory effects were enhanced with increasing concentrations. Therefore, multiple N sources in eutrophicated water induce different VOC emissions from cyanobacteria, and reduction in N can cause nutrient competition, which can result in emissions of more VOCs. Those VOCs released from M. flos-aquae cells under Non-N for nutrient competition can inhibit other algal growth. Among those VOCs, eucalyptol and limonene are the major toxic agents.

[Effects of azithromycin and Chlorella vulgaris treatment on certain cytokine values and NK cell activity in an acute murine toxoplasmosis model]. / Akut toksoplazmozlu fare modelinde Azitromisin ve Chlorella vulgaris'in tedavi etkinliginin, NK aktivasyonu ve bazi sitokin degerlerinin arastirilmasi.

Toxoplasmosis is a common infection with a complicated treatment process. Azithromycin (AZT) is a macrolide antibiotic that can be effectively used in patients with cerebral and ocular toxoplasmosis and has fewer side effects. Chlorella vulgaris (CV), a single-cell green algae that contains nutrients and has various biological effects. CV extract (CVE) has been shown to have protective effects against infections via immune enhancement by increasing the cytotoxicity of NK cells, IL-12 and IFN-γ levels. The aim of this study was to investigate the protective effects of AZT and CV, individually and in combination, against acute toxoplasmosis in mice, and their effects on NK cell cytotoxixity, IL-12, IFN-γ, and IL-2 levels. Six groups of mice (Balb/c) were formed. With the exception of the healthy control (HC) group, all other groups were infected with 1 ml (11 x 104 trofozoit/ml) Toxoplasma gondii RH strain trophozoites. No further action was performed for infected control (IC) group. After 24 hours from trophozoite infection, CVE was given to CV group, AZT to azithromycin group and CVE + AZT combination to CV + AZT group by oral gavage for 6 days. All of the mice from IC, CV, AZT and CV + AZT groups were sacrified on the 8th day of the infection and serum, peritoneal fluid and spleen samples were collected. Trophozoite count of the groups were determined in all groups except HC group and the average growth inhibition activity was calculated by using the growth inhibition formula. In all groups IL-12, IFN-γ, IL-2 levels were measured with ELISA method and cytotoxicity of the NK cells were measured using Cytotox 96 Non-Radioactive Cytotoxicity Assay. The number of trophozoites were significantly lower in the CV group than the IC group (p< 0.001), and also significantly lower in CV + AZT combination group than the AZT group. According to the growth inhibition calculations CV treatment showed 88.6%, AZT treatment 98.46%, AZT + CV combination treatment 99.4% antiprotozoal activity against T.gondii compared with the IC group. NK cell cytotoxicity in the CV and the combination group were significantly higher than all the other groups (p< 0.001). IL-12 and IFN-γ levels were highest in IC group and the lowest in AZT + CV group. This situation has been linked to the fact that the severity of the infection has fallen considerably. IL-2 levels were significantly higher in CV, CV + AZT groups than in the other groups (p< 0.001). In our study, even CV administration alone caused a significant decline in infection.This may be related to the increased NK cytotoxicity, IL-2, IL-12 and IFN-γ levels. CV + AZT combination seems to be an effective treatment option than AZT alone, particularly in patients who are difficult to treat with common methods or in patients with immunosuppression.

Bioavailability of wastewater derived dissolved organic nitrogen to green microalgae Selenastrum capricornutum, Chlamydomonas reinhardtii, and Chlorella vulgaris with/without presence of bacteria.

Effluent dissolved organic nitrogen (DON) is problematic in nutrient sensitive surface waters and needs to be reduced to meet demanding total dissolved nitrogen discharge limits. Bioavailable DON (ABDON) is a portion of DON utilized by algae or algae+bacteria, while biodegradable DON (BDON) is a portion of DON decomposable by bacteria. ABDON and BDON in a two-stage trickling filter (TF) wastewater treatment plant was evaluated using three different microalgal species, Selenastrum capricornutum, Chlamydomonas reinhardtii and Chlorella vulgaris and mixed cultured bacteria. Results showed that up to 80% of DON was bioavailable to algae or algae+bacteria inoculum while up to 60% of DON was biodegradable in all the samples. Results showed that C. reinhardtii and C. vulgaris can be used as a test species the same as S. capricornutum since there were no significant differences among these three algae species based on their ability to remove nitrogen species.

Multicellular group formation in response to predators in the alga Chlorella vulgaris.

A key step in the evolution of multicellular organisms is the formation of cooperative multicellular groups. It has been suggested that predation pressure may promote multicellular group formation in some algae and bacteria, with cells forming groups to lower their chance of being eaten. We use the green alga Chlorella vulgaris and the protist Tetrahymena thermophila to test whether predation pressure can initiate the formation of colonies. We found that: (1) either predators or just predator exoproducts promote colony formation; (2) higher predator densities cause more colonies to form; and (3) colony formation in this system is facultative, with populations returning to being unicellular when the predation pressure is removed. These results provide empirical support for the hypothesis that predation pressure promotes multicellular group formation. The speed of the reversion of populations to unicellularity suggests that this response is due to phenotypic plasticity and not evolutionary change.

Synergistic effect and mechanisms of compound bioflocculant and AlCl3 salts on enhancing Chlorella regularis harvesting.

The high energy input required for harvesting microalgae means that commercial production of microalgal biodiesel is economically unfeasible. In this study, we investigated the flocculation efficiency and synergistic mechanisms of novel coupled flocculants, AlCl3 and compound bioflocculants (CBF), to overcome this difficulty. AlCl3 flocculation was found to be very sensitive to pH, and flocculation efficiency increased from 55 to 95 % when pH increased from 4 to 10. CBF was environmental friendly, less reliant on pH, but had a relatively low flocculation of 75 % in optimum conditions. The harvesting efficiency of Chlorella regularis can achieve a satisfactory level of 96.77 % even in neutral conditions, with a CBF dosage of 0.26 g/L, AlCl3 dosage of 0.18 g/L, and coagulant aid (CaCl2) dosage of 0.12 g/L. Interestingly, compared with the use of single flocculant, the dosage of CBF, AlCl3, and coagulant aid (CaCl2) were reduced by about 52, 49, and 66 %, respectively. Besides, the aluminum (Al) ion content of the supernatant decreased significantly to a residue of only 0.03 mg/L, therefore meeting the downstream process needs easily. Patching and bridging played key roles in coupled flocculant flocculation, in which AlCl3 mainly carried out the electrical neutralization. This work provides new insight into an efficient, economical, and environmentally friendly protocol for microalgae harvesting.

Investigation of mixotrophic, heterotrophic, and autotrophic growth of Chlorella vulgaris under agricultural waste medium.

Growth of Chlorella vulgaris and its lipid production were investigated under autotrophic, heterotrophic, and mixotrophic conditions. Cheap agricultural waste molasses and corn steep liquor from industries were used as carbon and nitrogen sources, respectively. Chlorella vulgaris grew remarkably under this agricultural waste medium, which resulted in a reduction in the final cost of the biodiesel production. Maximum dry weight of 2.62 g L(-1) was obtained in mixotrophic growth with the highest lipid concentration of 0.86 g L(-1). These biomass and lipid concentrations were, respectively, 140% and 170% higher than autotrophic growth and 300% and 1200% higher than heterotrophic growth. In mixotrophic growth, independent or simultaneous occurrence of autotrophic and heterotrophic metabolisms was investigated. The growth of the microalgae was observed to take place first heterotrophically to a minimum substrate concentration with a little fraction in growth under autotrophic metabolism, and then the cells grew more autotrophically. It was found that mixotrophic growth was not a simple combination of heterotrophic and autotrophic growth.

The boosted lipid accumulation in microalga Chlorella vulgaris by a heterotrophy and nutrition-limitation transition cultivation regime.

A model of heterotrophy and nutrition-limitation transition cultivation for efficient algal biomass and lipid production was proposed in this study, wherein sufficient robust heterotrophic-seed cells submitted into nitrogen-starvation induction for boosted lipid accumulation. The results demonstrated that heterotrophic-seed (HS) achieved specific growth rate of 1.35 day-1 and biomass productivity of 1.93 mg/L/d, representing 6.42- and 32.16-fold, 2.01- and 2.75-fold more than that of photoautotrophic-seed (PS) and mixtrophic-seed (MS). Even though subsequent nutrition-limitation cultivation repressed the growth of HS, the overall lipid productivity caused by nitrogen-starvation was not offset by biomass loss. The most favorable lipid productivity (465.61 mg/L/d) of HS was 3.25 and 52.31 times higher than that of MS and PS. The high content of monounsaturated fatty acids (50.13%) over saturated and polyunsaturated fatty acids (totally 47.39%) in HS cells could provide superior oxidation stability and lower viscosity for biofuels generated from algal biomass feedstock. These findings suggested the feasibility of using heterotrophy and nutrition-limitation transition cultivation for enhancing the overall lipid productivity. Further, several critical enzymes (i.e. G3PDH, ME, and ACAD) were highly related to lipid accumulation and showed especially pronounced up-regulation or down-regulation expression in HS, which provide indications for shedding light on the molecular mechanisms of lipid accumulation and a prospective metabolic engineering for lipid production.

The role of phosphorus in the metabolism of arsenate by a freshwater green alga, Chlorella vulgaris.

A freshwater microalga, Chlorella vulgaris, was grown in the presence of varying phosphate concentrations (<10-500µg/L P) and environmentally realistic concentrations of arsenate (As(V)) (5-50µg/L As). Arsenic speciation in the culture medium and total cellular arsenic were measured using AEC-ICP-MS and ICP-DRC-MS, respectively, to determine arsenic biotransformation and uptake in the various phosphorus scenarios. At high phosphate concentration in the culture medium, >100µg/L P, the uptake and biotransformation of As(V) was minimal and dimethylarsonate (DMAs(V)) was the dominant metabolite excreted by C. vulgaris, albeit at relatively low concentrations. At common environmental P concentrations, 0-50µg/L P, the uptake and biotransformation of As(V) increased. At these higher As-uptake levels, arsenite (As(III)) was the predominant metabolite excreted from the cell. The concentrations of As(III) in these low P conditions were much higher than the concentrations of methylated arsenicals observed at the various P concentrations studied. The switchover threshold between the (small) methylation and (large) reduction of As(V) occurred around a cellular As concentration of 1fg/cell. The observed nearly quantitative conversion of As(V) to As(III) under low phosphate conditions indicates the importance of As(V) bio-reduction at common freshwater P concentrations. These findings on the influence of phosphorus on arsenic uptake, accumulation and excretion are discussed in relation to previously published research. The impact that the two scenarios of As(V) metabolism, As(III) excretion at high As(V)-uptake and methylarsenical excretion at low As(V)-uptake, have on freshwater arsenic speciation is discussed.

A Comparative Study on the Effects of Millisecond- and Microsecond-Pulsed Electric Field Treatments on the Permeabilization and Extraction of Pigments from Chlorella vulgaris.

The interdependencies of the two main processing parameters affecting "electroporation" (electric field strength and pulse duration) while using pulse duration in the range of milliseconds and microseconds on the permeabilization, inactivation, and extraction of pigments from Chlorella vulgaris was compared. While irreversible "electroporation" was observed above 4 kV/cm in the millisecond range, electric field strengths of ≥10 kV/cm were required in the microseconds range. However, to cause the electroporation of most of the 90 % of the population of C. vulgaris in the millisecond (5 kV/cm, 20 pulses) or microsecond (15 kV/cm, 25 pulses) range, the specific energy that was delivered was lower for microsecond treatments (16.87 kJ/L) than in millisecond treatments (150 kJ/L). In terms of the specific energy required to cause microalgae inactivation, treatments in the microsecond range also resulted in greater energy efficiency. The comparison of extraction yields in the range of milliseconds (5 kV, 20 ms) and microseconds (20, 25 pulses) under the conditions in which the maximum extraction was observed revealed that the improvement in the carotenoid extraction was similar and chlorophyll a and b extraction was slightly higher for treatments in the microsecond range. The specific energy that was required for the treatment in the millisecond range (150 kJ/L) was much higher than those required in the microsecond range (30 kJ/L). The comparison of the efficacy of both types of pulses on the extraction enhancement just after the treatment and after a post-pulse incubation period seemed to indicate that PEF in the millisecond range created irreversible alterations while, in the microsecond range, the defects were a dynamic structure along the post-pulse time that caused a subsequent increment in the extraction yield.