Bioprocess intensification and optimisation using macroscopic predictive models of cell culture processes

CHO cells, modeling, perfusion, ATF, segmented linear mode

Oil accumulation in the model green alga Chlamydomonas reinhardtii: characterization, variability between common laboratory strains and relationship with starch reserves

International audienceBackground: When cultivated under stress conditions, many microalgae species accumulate both starch and oil (triacylglycerols). The model green microalga Chlamydomonas reinhardtii has recently emerged as a model to test genetic engineering or cultivation strategies aiming at increasing lipid yields for biodiesel production. Blocking starch synthesis has been suggested as a way to boost oil accumulation. Here, we characterize the triacylglycerol (TAG) accumulation process in Chlamydomonas and quantify TAGs in various wild-type and starchless strains. Results: In response to nitrogen deficiency, Chlamydomonas reinhardtii produced TAGs enriched in palmitic, oleic and linoleic acids that accumulated in oil-bodies. Oil synthesis was maximal between 2 and 3 days following nitrogen depletion and reached a plateau around day 5. In the first 48 hours of oil deposition, a~80% reduction in the major plastidial membrane lipids occurred. Upon nitrogen re-supply, mobilization of TAGs started after starch degradation but was completed within 24 hours. Comparison of oil content in five common laboratory strains (CC124, CC125, cw15, CC1690 and 11-32A) revealed a high variability, from 2 μg TAG per million cell in CC124 to 11 μg in 11-32A. Quantification of TAGs on a cell basis in three mutants affected in starch synthesis (cw15sta1-2, cw15sta6 and cw15sta7-1) showed that blocking starch synthesis did not result in TAG over-accumulation compared to their direct progenitor, the arginine auxotroph strain 330. Moreover, no significant correlation was found between cellular oil and starch levels among the twenty wild-type, mutants and complemented strains tested. By contrast, cellular oil content was found to increase steeply with salt concentration in the growth medium. At 100 mM NaCl, oil level similar to nitrogen depletion conditions could be reached in CC124 strain. Conclusion: A reference basis for future genetic studies of oil metabolism in Chlamydomonas is provided. Results highlight the importance of using direct progenitors as control strains when assessing the effect of mutations on oil content. They also suggest the existence in Chlamydomonas of complex interplays between oil synthesis, genetic background and stress conditions. Optimization of such interactions is an alternative to targeted metabolic engineering strategies in the search for high oil yields

Coulomb matrix elements of bilayers of confined charge carriers with arbitrary spatial separation

We describe a practical procedure to calculate the Coulomb matrix elements of 2D spatially separated and confined charge carriers, which are needed for detailed theoretical descriptions of important condensed matter finite systems. We derive an analytical expression, for arbitrary separations, in terms of a single infinite series and apply a u-type Levin transform in order to accelerate the resulting infinite series. This procedure has proven to be efficient and accurate. Direct consequences concerning the functional dependence of the matrix elements on the separation distance, transition amplitudes and the diagonalization of a single electron-hole pair in vertically stacked parabolic quantum dots are presented.Comment: 8 page

Why people should run after positive affective experiences, not health benefits

International audienceMost individuals are now aware of health benefits of physical activity (PA) but remain physically inactive. Mobilizing a multidisciplinary approach at the crossroads between decision-making sciences, we investigate why highlighting the health benefits of PA is unlikely to promote a sustained engagement in PA. Essential features of decision making – effort-discounting, delay-discounting and beliefs distortion – may weaken the subjective value attributed to health benefits, making the latter insufficient to trigger PA behaviors. We develop a decision model demonstrating that health benefits hold a weak subjective value, in comparison with the cost of engaging in PA (e.g., effort) and of our innate attraction toward sedentary alternatives. Instead, focusing on positive affective experiences could counteract the impact of aforementioned features and ultimately favor a regular engagement in PA. Tackling the current pandemic of physical inactivity would therefore require an urgent change in the promotion of PA, so as to make affective experiences central

Why people should run after positive affective experiences instead of health benefits

International audienc

All’s well that ends well: an early-phase study testing lower end-session exercise intensity to promote physical activity in patients with Parkinson’s disease

Decreasing the intensity of exercise at the end of a session has been associated with greater post-exercise pleasure and enjoyment. Here, we investigated whether this manipulation can enhance affective attitudes toward physical activity (PA) and promote PA in patients with Parkinson’s disease (PD). Seven patients (72.9 ± 5.6 years, 3 women) were included in an eight-week within-subject study consisting of weekly exercise sessions. The first four weeks were used as a control condition. In the last four weeks, 9 minutes of lower-intensity exercise were added at the end of each session (experimental condition). Results of the linear mixed-effects models showed that the addition of lower-intensity exercise improved the explicit affective attitudes toward PA (b = 1.00, 95%CI = 0.36 to 1.64, P = 0.022). We found no evidence of an effect on implicit affective attitudes (P = 0.564), accelerometer-based PA (P = 0.417) and self-reported measures of PA (P = 0.122). Although not significant, self-reported PA per day was 36 minutes longer in the experimental than in the control condition. The findings of this early-phase study may suggest that reducing the intensity of an exercise at the end of the exercise sessions enhanced explicit affective attitudes toward PA in patients with PD. Yet, future well-powered and randomized studies are needed to provide more robust evidence

Relationships between changes in self-reported physical activity, sedentary behaviour and health during the coronavirus (COVID-19) pandemic in France and Switzerland

To assess whether changes in physical activity and sedentary behaviour during the COVID-19 lockdown are associated with changes in mental and physical health. Observational longitudinal study. Participants living in France or Switzerland responded to online questionnaires measuring physical activity, physical and mental health, anxiety, and depressive symptoms. Paired sample t-tests were used to assess differences in physical activity and sedentary behaviour before and during lockdown. Multiple linear regressions were used to investigate associations between changes in physical activity and changes in mental and physical health during lockdown. 267 (wave1) and 110 participants (wave2; 2 weeks later) were recruited. Lockdown resulted in higher time spent in walking and moderate physical activity (~10min/day) and in sedentary behaviour (~75min/day), compared to pre COVID-19. Increased physical activity during leisure time from week 2 to week 4 of lockdown was associated with improved physical health (β=.24, p=.002). Additionally, an increase in sedentary behaviour during leisure time was asso- ciated with poorer physical health (β=−.35, p=.002), mental health (β=−.25, p=.003), and subjective vitality (β=−.30, p=.004). Ensuring sufficient levels of physical activity and reducing sedentary time can play a vital role in helping people to cope with a major stressful event, such as the COVID-19 pandemic

Oil accumulation in the model green alga <it>Chlamydomonas reinhardtii</it>: characterization, variability between common laboratory strains and relationship with starch reserves

Abstract Background When cultivated under stress conditions, many microalgae species accumulate both starch and oil (triacylglycerols). The model green microalga Chlamydomonas reinhardtii has recently emerged as a model to test genetic engineering or cultivation strategies aiming at increasing lipid yields for biodiesel production. Blocking starch synthesis has been suggested as a way to boost oil accumulation. Here, we characterize the triacylglycerol (TAG) accumulation process in Chlamydomonas and quantify TAGs in various wild-type and starchless strains. Results In response to nitrogen deficiency, Chlamydomonas reinhardtii produced TAGs enriched in palmitic, oleic and linoleic acids that accumulated in oil-bodies. Oil synthesis was maximal between 2 and 3 days following nitrogen depletion and reached a plateau around day 5. In the first 48 hours of oil deposition, a ~80% reduction in the major plastidial membrane lipids occurred. Upon nitrogen re-supply, mobilization of TAGs started after starch degradation but was completed within 24 hours. Comparison of oil content in five common laboratory strains (CC124, CC125, cw15, CC1690 and 11-32A) revealed a high variability, from 2 μg TAG per million cell in CC124 to 11 μg in 11-32A. Quantification of TAGs on a cell basis in three mutants affected in starch synthesis (cw15sta1-2, cw15sta6 and cw15sta7-1) showed that blocking starch synthesis did not result in TAG over-accumulation compared to their direct progenitor, the arginine auxotroph strain 330. Moreover, no significant correlation was found between cellular oil and starch levels among the twenty wild-type, mutants and complemented strains tested. By contrast, cellular oil content was found to increase steeply with salt concentration in the growth medium. At 100 mM NaCl, oil level similar to nitrogen depletion conditions could be reached in CC124 strain. Conclusion A reference basis for future genetic studies of oil metabolism in Chlamydomonas is provided. Results highlight the importance of using direct progenitors as control strains when assessing the effect of mutations on oil content. They also suggest the existence in Chlamydomonas of complex interplays between oil synthesis, genetic background and stress conditions. Optimization of such interactions is an alternative to targeted metabolic engineering strategies in the search for high oil yields.</p