(746e) Carbon and Nitrogen Instationary Metabolic Flux Analysis On the Source Recovery Urea Cycle of a Unicellular Diatom

The urea cycle is known to produce urea from ammonia in vertebrates, thus enabling organs to remove excess nitrogen. It was previously assumed that this cycle operates only unidirectionally, always eliminating metabolized nitrogen. However, recent studies have found that in the unicellular, marine diatom Phaeodactylum tricornutum, this cycle may perform a biosynthetic role by assimilating nitrogen under nitrogen-depleted conditions. Previous studies have suggested (i) the operation of an incomplete ornithine-urea cycle in this diatom, and (ii) a role for amino acids such as aspartic acid and glutamic acid in nitrogen assimilation, perhaps in conjunction with the tricarboxylic acid cycle.

Diatoms are already known to be photosynthetically efficient. This, combined with an unusual role for the urea cycle, may explain the ecological success of diatoms in adapting to challenging environment. Yet, very little is known about fluxes through diatom metabolic pathways that facilitate carbon and nitrogen assimilation. In this presentation, we will report isotopes labeling experiments and metabolic flux analysis to elucidate fluxes through these pathways. Our metabolic flux analysis involves design of labeling experiments, isotopomer measurements using mass spectrometry and mathematical modeling of metabolic networks. We expect this analysis to reveal pathways of inorganic carbon and nitrogen assimilation including fluxes through the urea cycle and the interrelationship between the urea and tricarboxylic acid cycles. The coordination of nitrogen assimilation and photosynthesis will also be discussed, as well as the roles of these processes on biomass production.