The influence of acetate, CO2, and light on nitrogen-stress-induced formation of lipid bodies and 13C flux in C. reinhardtii

Zi Wang1, Jeremy King1, Sung Joon Kim2, and Ursula Goodenough1

1) Dept Biology, Washington University, St. Louis MO 63130 USA 2) Dept Chemistry, Washington University, St. Louis MO 63130 USA

We previously reported (Wang et al., Eukaryotic Cell 8: 1856-1868, 2009) that the cw15 wild-type strain of C.reinhardtii produces a 30-fold increase in lipid body (LB) production when starved for nitrogen (N) for 48 hr in the presence of 20 mM acetate, and that the cw15sta6 mutant, blocked in starch synthesis, produces a 60-fold increase. Here we report studies that analyze the contribution of exogenous acetate, CO2, and light to the LB production process. 1) No LB production is observed unless exogenous acetate is provided. 2) Provision of >20 - 100 mM acetate only modestly increases yield; > 100 mM is toxic (external pH is buffered). 3) Bubbling cultures with 5% CO2 fails to substitute for exogenous 20 mM acetate. 4) Induction in the dark in the presence of 20 mM acetate reduces LB yield by ~75%; we are currently testing the effects of the ac206 mutation, which lacks cytochrome 553 activity, on LB induction in the light to distinguish between the need for photosynthetic electron transport vs. some light-mediated signal. Cells induced under these various conditions are also being analyzed by solid state NMR using 13C acetate and 13CO2 to characterize the attendant carbon fluxes.

e-mail address of presenting author: Zi