Induction of oil accumulation by heat stress is metabolically distinct from N stress in the green microalgae Coccomyxa subellipsoidea C169

Abstract

Algae are often promoted as feedstock organisms to produce a sustainable petroleum fossil fuel alternative. However, to induce lipid accumulation most often requires a severe stress that is difficult to induce in large batch cultures. The objective of this study is to analyze and mathematically model heat stress on growth, chlorophyll content, triacylglyceride, and starch synthesis in algae. We initially screened 30 algal species for the most pronounced induction of lipid droplets from heat stress using confocal microscopy and mass spectroscopy techniques. One species, Coccomyxa subellipsoidea C169, was selected and subjected to further biochemical analyses using a jacketed bioreactor amended with 1% CO2 at 25°C, 30°C, 32°C, 33°C, 34°C, 35°C, and 36°C. Lipid and starch accumulation was less extreme than N stress. Growth was reduced above 25°C, but heat stress induced lipid droplet synthesis was negatively correlated with growth only past a demonstrated threshold temperature above 32°C. The optimal temperature for lipid accumulation was 35°C, which led to 6% of dry weight triglyceride content and a 72% reduction from optimal growth after 5 days. Fatty acid influx rates into triglycerides and 15N labeling of amino acids and proteins indicate that heat stress is mechanistically distinct from N stress. Thus, this study lends support to a novel hypothesis that lipid droplet triglycerides result from a redistribution of carbon flux as fatty acids to neutral storage lipids over membrane or other lipids.

Small heat shock protein genes of the green algae Closterium ehrenbergii: Cloning and differential expression under heat and heavy metal stresses

“…Similar results were noted in C. ehrenbergii when treated with copper, where similar morphological changes were observed, accompanied with fragmentation of intracellular chloroplast and loss of some cell contents . A recent study on Coccomyxa subellipsoidea revealed that the specific growth rates of the green microalgae decreased with increase in the temperature specially the chlorophyll content where they noted a drastic drop at high temperatures (33°C, 34°C, 35°C, and 36°C) . It also registered a decrease in the levels of chlorophyll in C. subellipsoidea cells with the increased temperature.…”

“…34 A recent study on Coccomyxa subellipsoidea revealed that the specific growth rates of the green microalgae decreased with increase in the temperature specially the chlorophyll content where they noted a drastic drop at high temperatures (33 C, 34 C, 35 C, and 36 C). 60 It also registered a decrease in the levels of chlorophyll in C. subellipsoidea cells with the increased temperature.…”

Kinetics and thermodynamics of lipids extraction from microalgae using n-hexane

“…In literature, there have been a lot of studies on its growth kinetics, and it's improvement on maximizing the biomass with maximum lipids [6][7][8][9][10][11]. Further, it's kinetic modeling and bioenergetics studies have been published [3,8,9,[11][12][13]. However, the kinetics and thermodynamics of extraction of oil from microalgae is not well studied.…”

Suboptimal Temperature Acclimation Affects Kennedy Pathway Gene Expression, Lipidome and Metabolite Profile of Nannochloropsis salina during PUFA Enriched TAG Synthesis

“…Previous work has shown that exposure to a broad range of temperatures results in fluctuations in the proportion of saturated and unsaturated fatty acids for membrane lipids, which contributes to cellular acclimation and photosynthetic thermo-stability [ 20 , 21 ]. Other than cold stress, several abiotic factors are directly involved in lipid accumulation in microalgae such as nitrogen deprivation, salinity, osmotic pressure, heat [ 22 ], chemicals, and drugs [ 23 , 24 ].…”