(495g) Probing Carbon Flow Patterns in a Photosynthetically Efficient Marine Diatom Toward Biofuel Production

Diatoms are unicellular, photosynthetic, marine algae that constitute a major component of phytoplankton. The abundant lipid content of diatoms motivates their use in the manufacture of lipid-derived biofuels such as biodiesel. The recent sequencing of diatom genomes has led to the hypothesis that diatom biochemistry is unusual as compared to that of other algae or plants. Specifically, the observation that diatoms exhibit high photosynthetic productivity (>20% of global photosynthetic productivity and molecular oxygen output) despite surviving in CO₂-depleted environments points to the operation of an efficient photosynthetic mechanism in them. However, a quantitative investigation of diatom biochemistry in terms of metabolic flux measurements through central carbon metabolism has not been reported in the literature. Performing this investigation will have implications toward engineering diatoms for improved CO₂ fixation and lipid production and ultimately toward engineering synthetic CO₂-sequestering devices.

Towards this objective we performed isotope-assisted metabolic flux analysis (MFA) on the model diatom Phaeodactylum tricornutum. This organism is an ideal choice for studying diatom biochemistry because both a sequenced genome and reverse genetics tools are available for it. In steady state isotope labeling experiments performed under constant light, we supplied P. tricornutum cultures with combinations of several ¹³C/¹²C carbon sources including CO₂ and glucose. We measured isotopomer abundances of biomass components such as proteinogenic amino acids by mass spectrometry, and employed metabolic network modeling to convert the isotopomer abundances to metabolic fluxes. In this presentation we will discuss how the isotopomer data and flux results from these experiments suggest atypical and previously unexpected metabolic flux patterns, such as the path traced by CO₂ through central carbon metabolism to lipids. We anticipate that the knowledge generated from this investigation to be pivotal towards developing metabolic engineering strategies for P. tricornutum and other diatoms.