Effect of nitrogen limitation on growth, biochemical composition, and cell ultrastructure of the microalga Picocystis salinarum

Abstract

In recent years, biodiesel production has attracted worldwide attention due to the awareness of fossil fuel depletion, and microalgae biomass is considered a promising raw material for its formulation. The present study evaluated the effects of different levels of nitrogen limitation (37.5, 18.75, 9.375 mg L -1 NaNO 3 ) on the growth, cell ultrastructure and biochemical composition of Picocystis salinarum as a potential raw material source for biodiesel. During a culture period of 20 days, the growth measurements were estimated, and cell density, dry weight and chlorophylls a, b content decreased with time as nitrogen limitation increase, however, carotenoids content increased. The high N limitation (9.375 mg L -1 ) had a highly signi cant effect on the accumulation of total lipid content (33.87% dry weight), carbohydrate content increase (30.98% dry weight), but protein content decrease (1.89% dry weight). The lipid content showed a differential FAME pro le with high saturated fatty acid values (996.08 µg g -1 dry weight) mainly C16:0, compare with the unsaturated ones that showed low values under high N limitation. The gradual increase of lipid content was also corroborated by transmission electron microscopy images with lipid droplet cell formation. Therefore, evaluation of the algal culture conditions such as N limitation, as a strategy to maximize lipid content and improve the fatty acid pro le in unexplored halophilic P. salinarum showed a potential biomass yield as a suitable candidate for biodiesel production.

Synergistic effect of nitrate exposure and heatwaves on the growth, and metabolic activity of microalgae, Chlamydomonas reinhardtii, and Pseudokirchneriella subcapitata

“…Nitrogen is an indispensable part of each polypeptide in protein structures 21,33 . A dramatic increase in protein levels with high nitrate concentration was expected, yet we observed a minimal change in both soluble and insoluble protein levels with different nitrate in the medium, similar to the previous observation made by Tarazona et al, (2021) 25 . Araújo and Garcia (2005) 34 found the protein content to be unaffected at lower temperatures (20 °C and 25 °C) compared to high temperatures (30 °C) in the diatom Chaetoceros cf.…”

“…With nitrate concentration, heatwaves synergistically increased both the soluble and insoluble sugar in microalgae. Similar to our study, Juneja et al, (2013) 25 also found an increase in sucrose (57%) in microalgae when exposed to 38 °C. The high sugar levels in microalgae during the heatwaves may help herbivores to fulfill the higher energy demand at higher temperatures 32 .…”

“…Growth was significantly lower in the nitrate-deprived medium even after long and intense heatwaves, and a synergistic increase in growth was observed at high nitrate during long and intense heatwaves. Moreover, the low nitrogen in the nitrate-deprived medium limited the chlorophyll concentrations which is also responsible for the low growth rate 25 . At the same time, the highest carotenoid concentration in high nitrate levels during the heatwaves may work as a protection against photodamaging and help to maintain the high growth rate 26 .…”

Elevated inorganic carbon and salinity enhances photosynthesis and ATP synthesis in picoalga Picocystis salinarum as revealed by label free quantitative proteomics

“…Krienitz et al (2012) states that "Picocystis salinarum from saline inland waters represents a link between marine and freshwater habitats from both an ecological and a phylogenetic point of view and is therefore of great interest. " Also, recent reports have suggested that Picocystis may have potential biotechnological applications from wastewater treatment (Ali et al, 2017;Ouada et al, 2018), to biofuel production (Wang et al, 2014;Delgado et al, 2021). In spite of demonstrating such unique environmental adaptations, flourishing and out competing other primary producers at extreme salinities and influencing the food web dynamics (Krienitz and Kotut, 2010), P. salinarum has gone unreported in most of the culture independent metagenomic studies of saline ecosystems all over, indicating the lack of information about this organism on molecular level.…”

Exploration of Microalgal Species for Nutrient Removal from Anaerobically Digested Swine Wastewater and Potential Lipids Production

“…In this regard, microalgae have emerged as a potential source for biodiesel production. In recent years, they have been considered as a third-generation biofuel feedstock that may replace traditional fossil fuels [13]. The use of microalgal biomass for biodiesel production is eco-friendly and sustainable.…”