Characterization of energy conversion based on metabolic flux analysis in mixotrophic liverwort cells, Marchantia polymorpha

Abstract

In order to characterize the contributions of respiratory and photosynthetic actions to energy conversions, the mixotrophic cells of Marchantia polymorpha were cultivated in the medium containing 10 kg/m 3 glucose as an organic carbon source. The cultures were conducted with the supply of ordinary air (0.03% CO 2) at constant incident light intensities of 50 and 180 W/m 2. From the results of metabolic analysis, it was found that the cell yield based on ATP synthesis was estimated to be 6.3×10 −3 kg-dry cells/mol-ATP in these cultures. Under the examined conditions, energy conversion efficiency through respiration was larger than that through photosynthesis, and efficiency of overall energy conversion to ATP was maximized when the sum of energies from glucose and light captured by the cells was ≈7.2×10 5 J/(h kg-dry cells). Taking into account the efficiency of overall energy conversion, a batch culture of M. polymorpha in a bioreactor was carried out by regulating incident light intensity ranging from 9 to 58 W/m 2. In the culture with light regulation, the cell yield of 6.2×10 −9 kg-dry cells/J was achieved on the basis of energy provided to the system throughout the culture, and this value was 2.3 and 9.3 times as large as those obtained in the cultures under constant incident light intensities of 50 and 180 W/m 2, respectively.