Genomic composition of green algae grown in high alkaline conditions

Abstract

Algae are responsible for 50% of global oxygen production and sequestration of CO 2 from the atmosphere. Algal photosynthesis plays a critical role in all aquatic ecosystems converting sunlight and CO2 into usable biomass. Algal growth and biomass production can be coopted to produce industrially relevant bioproducts like triacylglycerol (TAGs) that can be converted into biodiesel and provide a sustainable carbon-neutral alternative to fossil fuels. In high-stress environments, algae produce high levels of TAGs. Multiple stresses including nitrogen limitation and high pH impact algae physiology, but little is known about how algae shift their metabolism to produce TAGs in response to these stresses. This topic remains relatively unexplored due to the limited availability of complete algae genomes. Here we sequence and annotate the complete telomere-to-telomere genome of an alkali-tolerant green algae Chlorella sp. SLA-04. Genomic analysis supports a reclassification of Chlorophyta green algae and illuminates how SLA-04 adapts to diverse environmental conditions. Additionally, transcriptomic analysis revealed how Chlorella sp. SLA-04 rewires carbon metabolism in high alkaline and nutrient-deplete conditions to produce TAGs while minimizing photosynthetic oxidative stress. Together, we double the amount of publicly available telomere-to-telomere green algal genomes and use this resource to explore how algae respond to diverse environmental conditions in their native and industrial settings.