Accumulation of the Biodiesel Precursor Triacylglycerol Offsets Oxidative Stress in Chlamydomonas reinhardtii

Overview

Objectives/Goals Microalgae accumulate the biodiesel precursor triacylglycerol (TAG) when subjected to nutrient stress, a phenomenon that has become the basis for the field of algal biodiesel. Despite the promise of this technology as a carbon neutral alternative to fossil fuels, low oil yields have constrained adoption. This research seeks to increase oil yield by identifying the process that directly instigates TAG synthesis, which would allow oil accumulation to be induced without starving cells. The putative safety valve function of TAG in relieving electron buildups in the photosynthetic apparatus is evaluated. Methods/Materials Thin-layer chromatography (TLC) and Gas Chromatography Flame Ionization Detection (GCFID) were used to identify four redox-defective strains, three of which also demonstrated high growth kinetics. Chlorophyll fluorescence showed that photosynthetic electron transport rate and photosystem II yield were enhanced at low light intensities in the high-TAG mutants and provided evidence of excessive electron accumulation in the photosynthetic apparatus when TAG synthesis was halted. Results Blocking fatty acid synthesis caused the photosynthetic electron carrier plastoquinone to become highly reduced. This result demonstrates for the first time a causative link between reduction pressure and TAG accumulation, and indicates that offset of electron accumulation is a major physiological role of TAG. Four knockout strains that are defective in putative electron carriers where identified and shown to produce up to 30% more TAG than wild-type, as well as higher growth. Conclusions/Discussion The elucidation of this major physiological role of TAG accumulation in microalgae opens avenues for genetic engineering to enhance biodiesel yields. The four strains identified by this study simultaneously demonstrate high growth and TAG hyper-accumulation, and thus hold significant promise for industrial applications. By specifically activating the pathway that senses abnormal electron accumulation in the photosynthetic apparatus and signals TAG accumulation, biodiesel production can be achieved with no growth constraints.

Competition history

• CSEF 2015 Microbiology (General) · Entry S1503

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