Interactions between the CO2 concentrating mechanism and lipid production of two species of algae: Chlamydomonas reinhardtii and Nannochloropsis salina

The demand for energy is rapidly depleting available resources and creating a need for renewable energy. Wind and solar power are valuable sources of electricity, but they do not generate energy dense compounds needed for long distance uses such as long-haul trucking and air transportation. Algal lipid production may help to solve these needs without impacting food sources. However, many fundamental questions remain unanswered in algal biology and this is impairing development of viable algal lipid production systems. We have chosen to examine the basic research question of how algal CO₂ concentrating mechanism (CCM) function affects lipid production. CCM function is often induced at low CO₂ and it increases the efficiency of CO₂ capture, though the allocation of carbon under these conditions is not well understood. We analyzed lipid content and CCM function at low CO₂ (CCM expressed) and high CO₂ (CCM suppressed) to determine if CCM expression increases or decreases lipid storage. Our preliminary measurements of online carbon isotope discrimination showed that high CO₂ suppressed the CCM in both C. reinhardtii and N. salina. Our discrimination data also provided evidence for an unusual HCO₃^- pump-CO₂ leak style CCM in N. salina that was first characterized in other species of Nannochloropsis. In addition, our preliminary data using a hyperspectral imaging suggest lipid content increases in both species after exposure to high CO₂. However, the effect is smaller in C. reinhardtii and much of the lipid accumulation occurred in the eyespot.