Mechanical cell disruption of Parachlorella kessleri microalgae: Impact on lipid fraction composition.

Samples of nitrogen-starved Parachlorella kessleri containing intact cells (IC), cells ground by bead milling (BM), and cells subjected to high-pressure cell disruption (HPD), together with their supernatants after centrifugation, were compared for granulometry and lipid profiles. The effects of disruption on the lipid profile and organisation were evaluated. The quantity of lipids available for extraction increased with disruption, and up to 81% could be recovered in supernatants after centrifugation, but a marked reorganization occurred. The proportion of amphiphilic free fatty acids and lysophosphatidylcholine increased during disruption due to their release or owing to lipid degradation by enzymes or physical conditions. This effect was more marked in HPD than in BM. Lipids contained in the aqueous phase, after disruption and centrifugation, were enriched in unsaturated fatty acids, BM leading to larger droplets than HPD. The larger liquid lipid droplet would be easier to recover in the following downstream processing.

Screening of freshwater and seawater microalgae strains in fully controlled photobioreactors for biodiesel production.

Strain selection is one of the primary hurdles facing cost-effective microalgal biodiesel production. Indeed, the strain used affects both upstream and downstream biodiesel production processes. This study presents a screening procedure that considers the most significant criteria in microalgal biodiesel production including TAG production and wet extraction and recovery of TAGs. Fourteen freshwater and seawater strains were investigated. Large variation was observed between the strains in all the screening criteria. The overall screening procedure ultimately led to the identification of Parachlorella kessleri UTEX2229 and Nannochloropsis gaditana CCMP527 as the best freshwater and seawater strains, respectively. They featured the largest areal TAG productivity equal to 2.7×10(-3) and 2.3×10(-3)kgm(-2)d(-1), respectively. These two strains also displayed encouraging cell fragility in a high pressure bead milling process with 69% and 98% cell disruption at 1750bar making them remarkable strains for TAG extraction in wet environment.

Optimization of bead milling parameters for the cell disruption of microalgae: process modeling and application to Porphyridium cruentum and Nannochloropsis oculata.

A study of cell disruption by bead milling for two microalgae, Nannochloropsis oculata and Porphyridium cruentum, was performed. Strains robustness was quantified by high-pressure disruption assays. The hydrodynamics in the bead mill grinding chamber was studied by Residence Time Distribution modeling. Operating parameters effects were analyzed and modeled in terms of stress intensities and stress number. RTD corresponded to a 2 CSTR in series model. First order kinetics cell disruption was modeled in consequence. Continuous bead milling was efficient for both strains disruption. SI-SN modeling was successfully adapted to microalgae. As predicted by high pressure assays, N. oculata was more resistant than P. cruentum. The critical stress intensity was twice more important for N. oculata than for P. cruentum. SI-SN modeling allows the determination of operating parameters minimizing energy consumption and gives a scalable approach to develop and optimize microalgal disruption by bead milling.

Modifications in phospholipase D activity and isoform expression occur upon maturation and differentiation in vivo and in vitro in human myeloid cells.

Activation of phospholipase D (PLD) occurs in response to various stimuli and results from the activity of two isozymes, hPLD1 and hPLD2. PLD activity appears to be involved in several myeloid cell processes during their development and activation, including proliferation of myeloblasts in the bone marrow and secretion, phagocytosis and NADPH oxidase activation, essential functions of differentiated neutrophils. The present work studies PLD characteristics, activity and both isozyme expression during maturation and differentiation of myeloid cells by using three different systems: leukemic myeloblasts at different stages of maturation, terminally differentiated neutrophils ex vivo and four human myeloid cell lines, NB4, HL-60, PLB 985 and U937, induced to differentiate with alltrans retinoic acid (ATRA), a cyclic adenosine monophosphate (cAMP) analogue or both agents together. HL-60, a bipotential cell line has also been differentiated along the granulocytic pathway with DMSO and the monocytic pathway with 1,25-dihydroxy vitamin D3. In all these systems, PLD activity increases with maturation and differentiation whatever the inducer used and the granulocytic or monocytic pathways. Increase in basal activity which reflects the expression during development of both hPLD1 and hPLD2 appears to be mainly related to the former isozyme expression. Association of PLD characteristic changes with maturation and differentiation was also confirmed using two NB4 clones resistant to these processes. Comparison between PLD characteristics in myeloblasts during maturation and differentiation ex vivo and in vitro in the different cell lines demonstrated that NB4 induced to differentiate with ATRA represents the best model for further studies on the specific roles of each PLD isoform in various functions of differentiated myeloid cells.