Increased biomass productivity in green algae by tuning non-photochemical quenching

Photosynthetic microalgae have a high potential for the production of biofuels and highly valued metabolites. However, their current industrial exploitation is limited by a productivity in photobioreactors that is low compared to potential productivity. The high cell density and pigment content of the surface layers of photosynthetic microalgae result in absorption of excess photons and energy dissipation through non-photochemical quenching (NPQ). NPQ prevents photoinhibition, but its activation reduces the efficiency of photosynthetic energy conversion. In Chlamydomonas reinhardtii, NPQ is catalyzed by protein subunits encoded by three lhcsr (light harvesting complex stress related) genes. Here, we show that heat dissipation and biomass productivity depends on LHCSR protein accumulation. Indeed, algal strains lacking two lhcsr genes can grow in a wide range of light growth conditions without suffering from photoinhibition and are more productive than wild-type. Thus, the down-regulation of NPQ appears to be a suitable strategy for improving light use efficiency for biomass and biofuel production in microalgae

Refinement of the diagnostic approach for the identification of children and adolescents affected by familial hypercholesterolemia: Evidence from the LIPIGEN study

Background and aims: We aimed to describe the limitations of familiar hypercholesterolemia (FH) diagnosis in childhood based on the presence of the typical features of FH, such as physical sings of cholesterol accumulation and personal or family history of premature cardiovascular disease or hypercholesterolemia, comparing their prevalence in the adult and paediatric FH population, and to illustrate how additional information can lead to a more effective diagnosis of FH at a younger age.Methods: From the Italian LIPIGEN cohort, we selected 1188 (>= 18 years) and 708 (<18 years) genetically-confirmed heterozygous FH, with no missing personal FH features. The prevalence of personal and familial FH features was compared between the two groups. For a sub-group of the paediatric cohort (N = 374), data about premature coronary heart disease (CHD) in second-degree family members were also included in the evaluation.Results: The lower prevalence of typical FH features in children/adolescents vs adults was confirmed: the prevalence of tendon xanthoma was 2.1% vs 13.1%, and arcus cornealis was present in 1.6% vs 11.2% of the cohorts, respectively. No children presented clinical history of premature CHD or cerebral/peripheral vascular disease compared to 8.8% and 5.6% of adults, respectively. The prevalence of premature CHD in first-degree relatives was significantly higher in adults compared to children/adolescents (38.9% vs 19.7%). In the sub-cohort analysis, a premature CHD event in parents was reported in 63 out of 374 subjects (16.8%), but the percentage increased to 54.0% extending the evaluation also to second-degree relatives.Conclusions: In children, the typical FH features are clearly less informative than in adults. A more thorough data collection, adding information about second-degree relatives, could improve the diagnosis of FH at younger age

Photosynthetic response to nitrogen starvation and high light in Haematococcus pluvialis

Astaxanthin is a carotenoid mainly produced by microalgae upon exposure to stress conditions: this pigment has anti-oxidant, anti-inflammatory and anti-cancer capacity and it is widely used as pigmentation agent in different industrial sectors. Abiotic stresses such as exposure to high irradiances and/or nitrogen starvation are commonly used to induce astaxanthin biosynthesis in freshwater green alga Haematococcus pluvialis. In this work high light and nitrogen deprivation were applied as single or combined stresses in order to investigate their influence on the photosynthetic properties of H. pluvialis cultures. The results reported here demonstrate that nitrogen starvation inhibits chlorophyll biosynthesis and favors chlorophyll b degradation, chlororespiration and cyclic electron transport, while cells grown in high light are characterized by a higher destabilization of PSII. The combination of high light and nitrogen deprivation induced the highest astaxanthin production and also the fastest photoprotective response which cooperatively prevented Photosystem II from the damage observed in high light stress and nitrogen supplemented medium. In these conditions inhibition of astaxanthin accumulation leads to a reduced cell size but does not induce a higher photosensitivity of photosynthetic machinery

Il cloroplasto e la ricerca biologica per la produzione di cibo ed energia

La societ\ue0 moderna si trova difronte a un grave problema energetico: la popolazione mondiale \ue8 cresciuta da 2,5 miliardi nel 1950 a 7 miliardi nel 2011, e con essa \ue8 aumentata la domanda energetica, soddisfatta per 80% dai combustibili fossili. Per evitare una crisi energetica globale, \ue8 ormai evidente la necessit\ue0 di incrementare l'uso di fonti energetiche alternative. L'utilizzo di biomassa da microalghe per la produzione di biocarburanti, rinnovabili, biodegradabili, competitivi e zero emissioni di gas a effetto serra \ue8 un'interessante prospettiva, poich\ue9 la produzione di biomassa algale non compete per le terre coltivabili o per la domanda di cibo. Il compito della ricerca biotecnologica in questo campo \ue8 la domesticazione di specie algali per una migliore efficienza d'uso della luce e per aumentare il contenuto di lipidi. Questo permetter\ue0 di ridurre i costi di costruzione e gestione degli impianti fotobioreattore e del trattamento della biomassa

The function of LHCBM4/6/8 antenna proteins in Chlamydomonas reinhardtii

In eukaryotic autotrophs, photosystems are composed of a core moiety, hosting charge separation and electron transport reactions, and an antenna system, enhancing light harvesting and photoprotection. In Chlamydomonas reinhardtii, the major antenna of PSII is a heterogeneous trimeric complex made up of LHCBM1-LHCBM9 subunits. Despite high similarity, specific functions have been reported for several members including LHCBM1, 2, 7, and 9. In this work, we analyzed the function of LHCBM4 and LHCBM6 gene products in vitro by synthesizing recombinant apoproteins from individual sequences and refolding them with pigments. Additionally, we characterized knock-down strains in vivo for LHCBM4/6/8 genes. We show that LHCBM4/6/8 subunits could be found as a component of PSII supercomplexes with different sizes, although the largest pool was free in the membranes and poorly connected to PSII. Impaired accumulation of LHCBM4/6/8 caused a decreased LHCII content per PSII and a reduction in the amplitude of state 1-state 2 transitions. In addition, the reduction of LHCBM4/6/8 subunits caused a significant reduction of the Non-photochemical quenching activity and in the level of photoprotection

Non-photochemical quenching and xanthophyll cycle activities in six green algal species suggest mechanistic differences in the process of excess energy dissipation

In the present study the non-photochemical quenching (NPQ) of four biofilm-forming and two planktonic green algae was investigated by fluorescence measurements, determinations of the light-driven proton gradient and determination of the violaxanthin cycle activity by pigment analysis. It was observed that, despite the common need for efficient photoprotection, the structural basis of NPQ was heterogeneous in the different species. Three species, namely Chlorella saccharophila, Chlorella vulgaris and Bracteacoccus minor, exhibited a zeaxanthin-dependent NPQ, while in the three other species, Tetracystis aeria, Pedinomonas minor and Chlamydomonas reinhardtii violaxanthin de-epoxidation was absent or unrelated to the establishment of NPQ. Acclimation of the algae to high light conditions induced an increase of the NPQ activity, suggesting that a significant part of the overall NPQ was rather inducible than constitutively present in the green algae. Comparing the differences in the NPQ mechanisms with the phylogenetic position of the six algal species led to the conclusion that the NPQ heterogeneity observed in the present study was not related to the phylogeny of the algae but to the environmental selection pressure. Finally, the difference in the NPQ mechanisms in the different species is discussed within the frame of the current NPQ models

Improved lipid productivity in Nannochloropsis gaditana in nitrogen-replete conditions by selection of pale green mutants

Nannochloropsis gaditana is a photosynthetic unicellular microalgae considered one of the most interesting marine algae to produce biofuels and food additive due to its rapid growth rate and high lipid accumulation. Although microalgae are attractive platforms for solar energy bioconversion, the overall efficiency of photosynthesis is reduced due to the steep light gradient in photobioreactors. Moreover, accumulation of lipids in microalgae for biofuels production is usually induced in a two-phase cultivation process by nutrient starvation, with additional time and costs associated. In this work, a biotechnological approach was directed for the isolation of strains with improved light penetration in photobioreactor combined with increased lipids productivity