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

PLoS One. 2018 Sep 27;13(9):e0204505. doi: 10.1371/journal.pone.0204505. eCollection 2018.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biofuels*
  • Biomass
  • Bioreactors
  • Chlorophyll / metabolism
  • Chlorophyta / classification
  • Chlorophyta / growth & development
  • Chlorophyta / metabolism*
  • Fatty Acids / metabolism
  • Heat-Shock Response
  • Lipid Droplets / metabolism
  • Lipid Metabolism
  • Microalgae / classification
  • Microalgae / growth & development
  • Microalgae / metabolism*
  • Models, Biological
  • Nitrogen / metabolism
  • Phylogeny
  • Species Specificity
  • Starch / metabolism
  • Temperature
  • Triglycerides / metabolism

Substances

  • Biofuels
  • Fatty Acids
  • Triglycerides
  • Chlorophyll
  • Starch
  • Nitrogen

Grant support

The work was supported by the Nebraska Center for Energy Sciences Research under PN Black; Biochemical analysis of microalgae for enhanced oil synthesis and biomass in a wastewater system, Vestal W2O LLC and the Nebraska Department of Economic Development. The Vajra Instruments Inc. and Vestal W2O LLC provided support in the form of salaries for authors RT and JA, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.