Cell wall and organelle modifications during nitrogen starvation in Nannochloropsis oceanica F&M-M24

AbstractNannochloropsis oceanica F&M-M24 is able to increase its lipid content during nitrogen starvation to more than 50% of the total biomass. We investigated the ultrastructural changes and the variation in the content of main cell biomolecules that accompany the final phase of lipid accumulation. Nitrogen starvation induced a first phase of thylakoid disruption followed by chloroplast macroautophagy and formation of lipid droplets. During this phase, the total amount of proteins decreased by one-third, while carbohydrates decreased by 12–13%, suggesting that lipid droplets were formed by remodelling of chloroplast membranes and synthesis of fatty acids from carbohydrates and amino acids. The change in mitochondrial ultrastructure suggests also that these organelles were involved in the process. The cell wall increased its thickness and changed its structure during starvation, indicating that a disruption process could be partially affected by the increase in wall thickness for biomolecules recovery from starved cells. The wall thickness in strain F&M-M24 was much lower than that observed in other strains of N. oceanica, showing a possible advantage of this strain for the purpose of biomolecules extraction. The modifications following starvation were interpreted as a response to reduction of availability of a key nutrient (nitrogen). The result is a prolonged survival in quiescence until an improvement of the environmental conditions (nutrient availability) allows the rebuilding of the photosynthetic apparatus and the full recovery of cell functions

A simple method for rapid purification of phycobiliproteins from Arthrospira platensis and Porphyridium cruentum biomass

Membrane chromatography was exploited to purify allophycocyanin, phycocyanin and B-phycoerythrin from aqueous extracts of fresh or freeze-dried biomass of Arthrospira platensis (Cyanobacteria) and Porphyridium cruentum (Rhodophyta). The method can be tuned to obtain products having various degree of purity and avoids expensive and time consuming column chromatography and ultrafiltration steps. A commercial polyvinylidene fluoride (PVDF) microfiltration membrane (hydrophilic and low protein binding) was used as an ammonium sulphate responsive stationary phase to carry out the purification process. Analytical grade purity was achieved for phycocyanin (purity = 4.2–4.5, yield = 75–82 %) and B-phycoerythrin (purity = 4.5–4.8, yield = 69–71 %). Good purification, even if lower than analytical grade, was achieved for allophycocyanin (purity = 3.3–3.7, yield = 42–47%)

Photobioreactors for mass production of microalgae

Industrial exploitation of microalgae for feed, food, and biofuel production is currently limited by several factors, among which those connected with large-scale cultivation are of the greatest importance. Photobioreactors (closed systems for algae cultivation) suffer from high energy expenditures (mixing, cooling, and embodied energy), while open ponds have a more favorable energy balance. However, cultures in large-scale open ponds have a considerable water footprint, are unstable and maintaining selected strains in these systems for long periods is difficult. In the last years, thanks to the renewed interest in microalgae as feedstock for biofuels, many new photobioreactor designs have been proposed, most of them aiming at reducing costs. Besides improvements of the classic tubular and flat panel designs, some new concepts have been proposed, like hybrid systems combining open ponds and photobioreactors, and floating photobioreactors, which aim at exploiting water bodies instead of land for algae cultivation

Growth and photosynthetic performance of Chlamydopodium fusiforme cells cultivated in BG and Bristol media

Nitrogen is an essential nutrient for all life forms and its availability is periodically limited in marine and freshwater ecosystems. To optimize the growth of the freshwater microalga Chlamydopodium fusiforme and to investigate the cell acclimation process to different amounts of nitrogen, we grew cells in Bristol and BG11, under fixed conditions of 10:14 light/dark cycle. Cultures grown in BG11 exhibited higher biomass accumulation, reaching a cell dry weight of 1.94±0.1 g L -1 , while in Bristol it reached 1.58±0.1 g L -1 . In cells grown in BG11 chlorophyll content increased continuously up to 79.6 mg L -1 (9th day), while in Bristol was much lower (29.5 mg L -1 ). This fact caused a strong difference in their chlorophyll optical cross-sections and consequently in their photosynthetic performance (oxygen evolution and electron transport rate). Carotenoid content followed a similar pattern. It was interesting to note that despite this great difference in chlorophyll concentration, both photosynthesis rate and cell dry weight were not affected proportionally. The chlorophyll a fluorescence measurements indicated a stable effective quantum yield of photosystem II in both culture conditions. During the dark phase of the cycle we observed in both cultures a remarkable reduction of both electron transfer and photosynthesis rates, while maximum quantum yield of PSII remained stable (0.74±0.01). This indicated that the reduction in both photosynthesis rate and ETRmax observed during the dark phase were not due to damage of PSII reaction centers but rather to reduced flow of electron subsequent to PSII. Recovery of the fully photosynthetic capacity required about one hour of illumination

Purification of phycocyanin from Arthrospira platensis by hydrophobic interaction membrane chromatography

The cyanobacterium Arthrospira platensis is an important source of phycocyanin, which has many commercial applications in foods, cosmetics and pharmaceutics. In this study, hydrophobic interaction membrane chromatography (HIMC) was used for the first time to separate phycocyanin from allophycocyanin and obtain analytical grade phycocyanin, avoiding packed bed (i.e., packed column) chromatography steps. The extraction of phycobiliproteins was carried out on freeze-dried biomass samples suspended in NaCl 0.1 M, and the phycobiliprotein crude extract was obtained by centrifuging the suspension to eliminate cell debris. The crude extract, after the addition of an appropriate amount of ammonium sulphate, was loaded on an ammonium sulphate responsive commercial hydrophilic polyvinylidene fluoride (PVDF) membrane for the HIMC purification process. Applying a two-step HIMC purification procedure, a phycocyanin purity ratio of 4.20 and a yield of 67.0% was attained

Cold preservation and use of microalgae aquaculture feeds

No abstract availabl

High surface-to-volume ratio photobioreactors used at the University of Florence for the cultivation of microalgae

No abstract availabl

Outdoor mass cultivation of Nannochloropsis in Annular reactors

No abstract availabl