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Different behaviour between autotrophic and heterotrophic Galdieria sulphuraria (Rhodophyta) cells to nitrogen starvation and restoration. Impact on pigment and free amino acid contents
No full textThe unicellular red alga Galdieria sulphuraria is a polyextremophilic organism with a metabolic flexibility to grow autotrophically or heterotrophically. Galdieria can also produce and accumulate biotechnologically attractive products such as pigments (phycocyanin) and proteins. In this research we studied the effects of nitrogen starvation and its subsequent restoration on pigment and free amino acid contents both in photoautotrophic and heterotrophic cells. Following the nitrogen starvation, the levels of the primary photosynthetic pigments decreased both in autotrophic and heterotrophic cells, except for the chlorophyll a marginally diminished in heterotrophic cells. Ammonium supply to G. sulphuraria N starved cells caused a significant increase of total chlorophylls both in autotrophic and heterotrophic cells. It was observed how such increase was more rapid and marked in heterotrophic cells than in the autotrophic ones. Under N starvation, phycocyanin contents decreased in both autotrophic and in heterotrophic cells; however, after a time-lapse of 24 hours, they resulted significantly higher in heterotrophic cells. In Galdieria sulphuraria, like in other microalgae, free amino acid contents were profoundly dependent on nitrogen status of the cells but heterotrophic cells maintained much higher levels, especially of glutamate, respect to autotrophic ones. In general, cells grown in the presence and absence of light showed different responses toward N availability; in particular heterotrophic cells seemed to respond quicker to the ammonium restoration compared to autotrophic ones
Sulfur Starvation in Extremophilic Microalga Galdieria sulphuraria: Can Glutathione Contribute to Stress Tolerance?
Full text linkThis study reports the effects of sulfur (S) deprivation in cultures of Galdieria sulphuraria (Cyanidiophyceae). Galdieria is a unicellular red alga that usually grows, forming biomats on rocks, in S-rich environments. These are volcanic areas, where S is widespread since H2S is the prevalent form of gas. The glutathione content in Galdieria sulphuraria is much higher than that found in the green algae and even under conditions of S deprivation for 7 days, it remains high. On the other hand, the S deprivation causes a decrease in the total protein content and a significant increase in soluble protein fraction. This suggests that in the conditions of S starvation, the synthesis of enzy-matic proteins, that metabolically support the cell in the condition of nutritional stress, could be up regulated. Among these enzymatic proteins, those involved in cell detoxification, due to the accumulation of ROS species, have been counted
Chlorella sorokiniana dietary supplementation increases antioxidant capacities and reduces ros release in mitochondria of hyperthyroid rat liver
Full text linkThe ability of aerobic organisms to cope with the attack of radicals and other reactive oxygen species improves by feeding on foods containing antioxidants. Microalgae contain many molecules showing in vitro antioxidant capacity, and their food consumption can protect cells from oxidative insults. We evaluated the capacity of dietary supplementation with 1% dried Chlorella sorokiniana strain 211/8k, an alga rich in glutathione, α-tocopherol, and carotenoids, to counteract an oxidative attack in vivo. We used the hyperthyroid rat as a model of oxidative stress, in which the increase in metabolic capacities is associated with an increase in the release of mitochondrial reactive oxygen species (ROS) and the susceptibility to oxidative insult. Chlorella sorokiniana supplementation prevents the increases in oxidative stress markers and basal oxygen consumption in hyperthyroid rat livers. It also mitigates the thyroid hormone-induced increase in maximal aerobic capacities, the mitochondrial ROS release, and the susceptibility to oxidative stress. Finally, alga influences the thyroid hormone-induced changes in the factors involved in mitochondrial biogenesis peroxisomal proliferator-activated receptor-γ coactivator (PGC1-1) and nuclear respiratory factor 2 (NRF-2). Our results suggest that Chlorella sorokiniana dietary supplementation has beneficial effects in counteracting oxidative stress and that it works primarily by preserving mitochondrial function. Thus, it can be useful in preventing dysfunctions in which mitochondrial oxidative damage and ROS production play a putative role
Enhancement of Pigments Production by Nannochloropsis oculata Cells in Response to Bicarbonate Supply
No full textIn this study, the effects of bicarbonate addition on growth and pigment contents of the unicellular microalga Nannochloropsis oculata, were evaluated. N. oculata represents an interesting source of biomolecules widely used for food supplements and nutraceuticals. The bicarbonate was supplemented to microalgae cultures at concentrations of 0, 6, 18, 30, 42 and 60 mM. The cultures supplemented with salt at highest concentrations (42 and 60 mM) showed a significant increase in algal growth, demonstrated by the optical density spread. The intracellular content of pigments such as chlorophyll a and total carotenoids reached the highest values in cells from cultures supplied with bicarbonate. In fact, concentrations of bicarbonate from 30 to 60 mM strongly improved, for a short period of only 72 h, the cellular levels of chlorophylls and carotenoids. These are interesting pigments with commercial applications. The utilization of bicarbonate could represent an interesting sustainable opportunity to improve microalgae cultivation for cellular growth and pigment contents
Heterotrophic Cultures of Galdieria phlegrea Shift to Autotrophy in the Presence or Absence of Glycerol
No full textDespite being an autotrophic organism, Galdieria phlegrea (Galdieriaceae) has the ability to use glycerol thereby switching to heterotrophy in the dark and mixotrophy in the presence of light. To examine cellular changes during the switch to mixotrophic metabolism and finally to photoautotrophic metabolism, heterotrophic cells of G. phlegrea were exposed to light and split into two subcultures. Cells exposed only to light but cultivated in medium containing glycerol grew with a recovery time of at least 3 days. In a parallel culture, the simultaneous removal of glycerol from the culture medium and light exposure allowed Galdieria cells to rapidly recover their growth rate due to their ability to rapidly absorb ammonium from the medium. However, contrary to expectation, a higher content of total soluble protein was observed in light-exposed cells cultivated in medium containing glycerol compared to cells cultivated without glycerol. In addition, the level of Rubisco in cells exposed to light and cultivated without glycerol was higher than those in cells cultivated in medium containing glycerol, indicating full photosynthetic functionality after only 3 days of light treatment. The greater chlorophyll a content confirms that the photosynthetic activity of cells cultivated without glycerol recovers earlier than that of heterotrophic cells exposed to light but still cultivated in medium containing glycerol
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Microalgae cross-fertilization: short-term effects of Galdieria phlegrea extract on growth, photosynthesis and enzyme activity of Chlorella sorokiniana cells
No full textGaldieria spp. (Rhodophyta) are polyextremophile microalgae known for their important antioxidant properties in different biological systems. Nowadays, the beneficial and bio-stimulant effect of microalgal extracts is widely tested on crops. Here, for the first time, potential positive effects of aqueous extracts from Galdieria were tested on a second microalgal culture systems. Chlorella sorokiniana cultures were supplemented with Galdieria phlegrea extracts (EC) and the short-term (48 h) effects of extract addition on growth and biochemical and physiological parameters were monitored and compared to those of non-supplemented Chlorella (CC). Growth of Chlorella was improved in EC as shown by higher optical density and cells number in the enriched cultures. In addition, EC appreciably increased the pigments (chlorophyll (a and b) and carotenoids) contents of Chlorella cells. Increase of photosynthetic pigments was associated with higher photosynthesis and lower non-radiative dissipation of light in EC as indicated by chlorophyll fluorescence parameters. Reduced activities of antioxidant enzymes (SOD, CAT and APX), but increased total antioxidant capacity (ABTS) were observed in EC, suggesting that this culture was under a low oxidative status, but can activate antioxidant defences if exposed to oxidative stress. In conclusion, a short-term positive effect of the addition of G. phlegrea extracts on growth and physiology of C. sorokiniana was demonstrated
Different characteristics of C-phycocyanin (C-PC) in two strains of the extremophilic Galdieria phlegrea
No full textTo date, the main source for phycocyanin production is the thermophilic cyanobacterium Spirulina platensis, although latest researches are exploring the possibility to exploit the thermoacidophilic Cyanidiophyceae (Rhodophyta) to this purpose. Galdieria phlegrea is a polyextremophilic red alga belonging to Cyanidiophyceae, colonizing, along with G. sulphuraria, acidic and thermal environments and distinguishable from this latter on the base of molecular and ecophysiological traits. In the present paper, a characterization of C-phycocyanin from two strains of G. phlegrea with different geographic provenance (Phlegrean Fields Naples, Italy; Diyadin, Turkey) was provided under autotrophic and heterotrophic conditions. The results showed different optimal pHs and thermostability between the strains and between autotrophic and heterotrophic cells. What is intriguing, a pre-heating at 70 °C of heterotrophic cells from the Italian strain resulted in a highly heat-resistant of C-phycocyanin. We hypothesized that the different features of this pigment, currently widely used for various applicative purposes, are related to the habitat from which the microalga comes from
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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