13C metabolic flux analysis (MFA) to find out the metabolic fluxes of biomass production and lipid accumulation in Neochloris oleoabundans UTEX 1185

Abstract

Neochloris oleoabundans UTEX 1185 is a green microalga that is considered as a promising feedstock for microalgal biodiesel production as it contains high amount of lipids. Our preliminary work has shown that a faster growth, more biomass, and higher lipid content could be achieved in mixotrophic mode of growth of the strain in medium with reduced nitrate concentration. In order to estimate the central carbon flux distribution of N. oleoabundans UTEX 1185 under these conditions that improve lipid productivity, we conducted a stationary 13C-metabolic flux analysis (MFA). Our study shows that in addition to Calvin-Benson-Bassham (CBB) and tricarboxylic acid (TCA) cycles, the glyoxylate shunt is active, and a positive flux for the synthesis of storage carbohydrates was also observed in the mixotrophic growth condition. Consistent with the increased lipid content of the organism, about 33% of carbon taken up goes to the acetyl-CoA sink. A comparison of the flux distributions in the metabolic networks with and without the Entner-Doudoroff (ED) pathway showed that the network with ED pathway gave a more plausible flux distribution and suggested that ED pathway is active under the conditions tested. Therefore, this work provides quantitative assessment of the activity of the major pathways associated with growth and lipid production of N. oleoabundans under mixotrophy in reduced N condition.