Abstract
Temperature and light are two of the most crucial factors for microalgae production. Variations in these factors alter their growth kinetics, macromolecular composition and physiological properties, including cell membrane permeability and fluidity. The variations define the adaptation mechanisms adopted by the microalgae to withstand changes in these environmental factors. In the Qatar desert the temperature varies widely, typically between 10° and 45 °C There are also wide variations in light intensity, with values of over 1500 μmolhν.m−2s−1 in summer. A study of the effects of these thermal and light fluctuations is therefore essential for large-scale outdoor production systems, especially during the summer when temperature and light fluctuations are at their highest. The aim of this work is to study the impact of temperature and light intensity variations as encountered in summer period on the Nannochloropsis QU130 strain, which was selected for its suitability for outdoor cultivation in the harsh conditions of the Qatar desert. It was carried out using lab-scale photobioreactors enabling simulation of both constant and dynamic temperature and light regimes. Biomass productivity, cell morphology and biochemical compositions were examined first in constant conditions, then in typical outdoor cultivation conditions to elucidate the adjustments in cell function in respect of fluctuations. The dynamic light and temperature were shown to have interactive effects. The application of temperature cycles under constant light led to a 13.6% increase in biomass productivity, while a 45% decrease was observed under light and temperature regimes due to the combined stress. In all cases, the results proved that N. sp. QU130 has a high level of adaptation to the wide fluctuations in light and temperature stress. This was shown through its ability to easily change its physiology (cell size) and metabolic process in response to different cultivation conditions.
Highlights
Microalgae are ubiquitous photosynthetic microorganisms that consume CO2, light, and inorganic nutrients to produce biomass, which is rich in compounds such as lipids, carbohydrates, proteins, and pigments [1]
The biochemical composition of the microalgae varies according to the nature of the microalgae, the cell density, the growth phase, and the culture conditions, such as temperature, pH, salinity, CO2 concentration, medium composition, and light intensity [2]
When the day/night cycle stress (Regime C) was applied to a steady-state culture obtained at constant continuous light and temperature, an immediate and sharp 50%
Summary
Microalgae are ubiquitous photosynthetic microorganisms that consume CO2 , light, and inorganic nutrients to produce biomass, which is rich in compounds such as lipids, carbohydrates, proteins, and pigments [1]. The biochemical composition of the microalgae varies according to the nature of the microalgae, the cell density, the growth phase, and the culture conditions, such as temperature, pH, salinity, CO2 concentration, medium composition, and light intensity [2]. It has been observed that there are species-dependent requirements for optimal growth and metabolite accumulation, e.g., Chlorella pyrenoidosa requires an optimal daytime temperature of 31 ◦ C and an illumination of 420 μmolhν .m−2 s−1 , with a photoperiod of 16:8 h light:dark for maximum biomass and lipid production [4]. 2012 proved that growing Chlamydomonas reinhardtii cc124 in a 12 h:12 h photoperiod regime reduced both the algal growth rate and the cell density by approximately 30% compared to continuous light conditions [6]; Ruangsomboon et al, 2012 observed that Botryococcus braunii
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