1,720,994 research outputs found
Selection of microalgae in artificial digestate: Strategies towards an effective phycoremediation
Full text linkDigestate is a complex by-product of anaerobic digestion and its composition depends on the digestor inputs. It can be exploited as a sustainable source of nutrients for microalgae cultivation but its unbalanced composition and toxic elements make the use challenging. Screening algae in a simplified synthetic digestate which mimics the main nutrient constraints of a real digestate is proposed as a reproducible and effective method to select suitable species for real digestate valorisation and remediation. Growth performance, nutrient removal and biomass composition of eight microalgae exposed to high amounts of NH4+, PO4− and organic-C were assessed. Using a score matrix, A. protothecoides, T. obliquus, C. reinhardtii, and E. gracilis were identified as the most promising species. Thus, three strategies were applied to improve outcomes: i) establishment of an algal consortium to improve biomass production, ii) K+ addition to the medium to promote K+ uptake over NH4+ and to reduce potential NH4+ toxicity, iii) P starvation as pretreatment for enhanced P removal by luxury uptake. The consortium was able to implement a short-term response displaying higher biomass production than single species (3.77 and 1.03–1.89 mg mL−1 respectively) in synthetic digestate while maintaining similar nutrient remediation, furthermore, its growth rate was 1.6 times higher than in the control condition. However, the strategies aiming to reduce NH4+ toxicity and higher P removal were not successful except for single cases. The proposed algal screening and the resulting designed consortium were respectively a reliable method and a powerful tool towards sustainable real digestate remediatio
Sulfur and phytoplankton: acquisition, metabolism and impact on the environment
No full textSulfur emission from marine phytoplankton has been recognized as an important
factor for global climate and as an entry into the biogeochemical S cycle. Despite
this significance, little is known about the cellular S metabolism in algae that forms
the basis of this emission. Some biochemical and genetic evidence for regulation of S
uptake and assimilation is available for the freshwater model alga
Chlamydomonas
.
However, the marine environment is substantially different from most freshwaters,
containing up to 50 times higher free sulfate concentrations and challenging the
adaptive mechanisms of primary and secondary S metabolism in marine algae. This
review intends to integrate ecological and physiological data to provide a comprehensive
view of the role of S in the oceans
Ecophysiological behaviour of different diatoms in response to copepod signals
Full text linkPhytoplanktonic communities have been moulded from a higher level in the food web by zooplankton
predation. Diatoms, which are the major primary producers in present day oceans, have evolved many
strategies to thrive in the presence of copepods, their predators. Chemical signals are released in the
aquatic environment by microarthropods and elicit morphological, behavioural and/or physiological
modifications in diatom cells which allow them to cope with predators. Other than the most studied
effects of copepod signals on the release of toxins by diatoms, the role of chemical cues on growth and
biology of non-toxic diatoms has been little investigated, although it may broaden our knowledge of coevolutive
physiological mechanisms. To examine the response of diatoms to copepod-derived signals,
Phaeodactylum tricornutum, Chaetoceros muelleri and Cylindrotheca fusiformis (Bacillariophyceae) were
grown in the presence of copepod cues. Physiological modifications occurred and differed in sign and
magnitude between species: i) in P. tricornutum cell density was higher, and dry weight lower, suggesting
energy allocation into cell division at the expense of lipid and protein quotas; ii) C. muelleri showed
a very homeostatic behaviour; and iii) in C. fusiformis cell density was lower and lipid content higher,
showing energy allocation into lipids, which likely act as deterrent to feeders. Copepod cues are here
suggested to have ruled diatom species composition in the ocean by affecting species-specific growth
performance and the energy allocation into macromolecules
Role of phosphoenolpyruvate carboxylase in anaplerosis in the green microalga Dunaliella salina cultured under different nitrogen regimes
No full textAnaplerosis plays a very important role in providing C for N assimilation. In green algae and higher plants, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) is the main anaplerotic carboxylase. On this basis we hypothesize that N availability affects PEPC expression. In order to test this hypothesis, the model organism Dunaliella salina was cultured under a variety of N growth regimes. Our results show that the level of PEC activity was unaffected by the N form in which N was supplied to the cells, when N concentration was low (0.5–0.01 mM). When cells were adapted to growth at 5 mM N, however, PEPC activity on a per cell basis was substantially higher in NH4+-adapted cells as compared to their NO3–-adapted counterparts; however, the same difference was not observed on a protein basis. This notwithstanding, even at low N, PEPC of cells cultured in the presence of either NH4+ or NO3– appeared to differ in their molecular masses. These results suggest that cells adapted to different N-form express distinct PEPC isoforms. In addition to this, we observed that, in algae adapted to high (5 mM) NH4+ concentration, a PEPC isoform was induced that differed from the isoforms observed in algae adapted to lower concentrations of the same N-source. These findings lead us to conclude that the expression of PEPC isoforms in D. salina responds to the variation in the C-skeleton demand deriving from changes in the chemical form and availability of N
Monocultures vs. polyculture of microalgae: unveiling physiological changes to facilitate growth in ammonium rich-medium
Full text linkDue to the increasing production of wastewater from human activities, the use of algal consortia for phytoremediation has become well-established over the past decade. Understanding how interspecific interactions and cultivation modes (monocultures vs. polyculture) influence algal growth and behaviour is a cutting-edge topic in both fundamental and applied science. Ammonium-rich growth media were used to challenge the monocultures of Auxenochlorella protothecoides, Chlamydomonas reinhardtii and Tetradesmus obliquus, as well as their polyculture; NO3− was also used as the sole nitrogen chemical form in control cultures. The study primarily compared the growth, carbon and nitrogen metabolisms, and protein content of the green microalgae monocultures to those of their consortium. Overall, the cultivation mode significantly affected all the measured parameters. Notably, at 50 mM NH4+, the assimilation rates of carbon and nitrogen were at least twice as high as those in the monoculture counterparts, and the protein content was three times more abundant.Additionally, the consortium's response to NH4+ toxicity was investigated by observing a linear relationship between the indicator of tolerance to NH4+ nutrition and the N isotopic signature. The study highlighted a high degree of acclimation through metabolic flexibility and diversity, as well as species abundance plasticity in the consortium, resulting in a functional resilience that would otherwise have been unattainable by the respective monoculture
PHYSIOLOGICAL RESPONSES OF PHAEODACTYLUM TRICORNUTUM AND CYLINDROTHECA CLOSTERIUM (BACILLARIOPHYCEAE) TO DIFFERENT N-REGIMES
No full textPoster PIV04 pg. 5
Taxonomy and growth conditions concur to determine the energetic suitability of fatty acid complements in algae
No full textWe hypothesize that, in algae, carbon allocation to lipids depends on the combined effects of the metabolic constraints imposed by the genotype (i.e., species-specific differences in composition) and on the acclimation responses (phenotype) to changes in the stoichiometry of available inorganic carbon (for photosynthesis) and nitrogen (primarily for amino acids, protein, and nucleic acid synthesis). We thus cultured three taxonomically distinct algae, the green alga Dunaliella salina, the diatom Thalassiosira pseudonana, and the dinoflagellate Protoceratium reticulatum, at four nitrate concentrations and constant inorganic carbon. Since energy availability also directly impacts carbon partitioning, we studied the effect of irradiance on the oil quality of P. reticulatum. We used Fourier transform infrared (FTIR) spectroscopy to study carbon allocation and biomass reduction level and gas chromatography for fatty acid analysis. The fatty acid complements of the three species were different; within each species, growth conditions substantially altered oil quality. We ranked the oils in terms of their suitability as biodiesels, using international standards as reference. We believe that this approach may help to identify the appropriate combination of taxa and culture conditions for algal biodiesel production and in general offers insight on carbon allocation to fatty acids
Influence of the nitrogen source and metabolites on phosphoenolpyruvate carboxylase activity in the unicellular green alga Dunaliella parva ccap 19/9
No full textThe activity of phosphoenolpyruvate carboxylase (PEPC) was measured in cell-free extracts of the salt-tolerant unicellular green alga Dunaliella parva Lerche CCAP 19/9. For cells grown in batch cultures with 5 mM NaNO3 as the sole source of nitrogen, the optimum pH for PEPC activity was 8 and the reaction was saturated by 1 mM phosphoenolpyruvate (PEP). The K0.5 for PEP was 150 μM and the Vmax was 0.18 ± 0.04 μmol h−1 mg−1 soluble protein. The effect of key metabolites on PEPC activity was determined under optimum assay conditions. Glycerol, the main osmoticum of Dunaliella, had little or no effect on PEPC activity, but dihydroxyacetone phosphate, pyruvate, α-ketoglutarate, orthophosphate, glutamine, glutamate and aspartate all stimulated activity. Surprisingly, the largest stimulation was exerted by aspartate, generally an inhibitor of PEPC, which enhanced PEPC activity up to 30-fold. Oxaloacetate slightly inhibited PEPC activity, but the most effective inhibitor was malate, which caused an 80–90% decrease in the carboxylation, even at low concentration. The response of PEPC activity to replacement of NaNO3 with NH4Cl was tested in continuous culture. The activity of PEPC increased when NH4+ was added to the medium and, even if it decreased somewhat during acclimation to the new nitrogen source, it stayed at levels that were appreciably higher than those observed in NO3−-grown cells. These results are discussed with regard to the role that PEPC may play under different nitrogen growth regimes
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