Fucoxanthin biosynthesis has a positive correlation with the specific growth rate in the culture of microalga Phaeodactylum tricornutum

Abstract

In this study, the correlation between the specific growth rate of Phaeodactylum tricornutum and fucoxanthin (fucoxanthin) biosynthesis was investigated both in batch and in semi-continuous cultures. Fucoxanthin content from P. tricornutum biomass showed a positive correlation with specific growth rate during the normal culture period. The maximum yield of fucoxanthin (2.42 mg g(-1) dry biomass) was observed at day 5, and the highest specific growth rate (1.91) was observed at day 4, both of which were during the exponential phase. Upon treatment with growth inhibitors (AZD-8055 or norflurazon) during the exponential phase, fucoxanthin content decreased with growth rate in a concentration-dependent manner. In a semi-continuous culture of P. tricornutum with dilution rates from 0.1 to 0.5 day(-1), we found a positive correlation between specific growth rate and fucoxanthin biosynthesis in a steady-state condition. Based on the transcriptome analysis results, different metabolic and key regulatory genes were active at different growth phases. Particularly, during the exponential growth phase, various genes related to regulatory mechanisms, such as cell growth and replication, were expressed, whereas in the stationary phase, their expression was reduced. In the fucoxanthin biosynthesis pathway, 1-deoxy-d-erythritol 2,4-cyclodiphosphate synthase (ISPD) and violaxanthin deepoxidase (VDE) genes showed higher expression levels in the exponential phase, thus indicating that they are critical genes for the regulation of fucoxanthin biosynthesis in P. tricornutum. Our results are valuable to our understanding of the basic mechanism of fucoxanthin biosynthesis, thus providing theoretical guidance for the commercial production of fucoxanthin derived from P. tricornutum.