Transcriptomics and Metabolomics Analyses Provide Novel Insights into Glucose-Induced Trophic Transition of the Marine Diatom Nitzschia laevis.

Xuemei Mao,Jianfeng Yu,Xia Wang,Feng Chen,Bin Liu,Xiaojie Li,Mengdie Ge

doi:10.3390/md19080426

Abstract

Diatoms have important ecological roles and are natural sources of bioactive compounds. Nitzschia laevis is a member of marine diatoms that accumulates high-value products including fucoxanthin and eicosapentaenoic acid (EPA). In this study, physiological data showed that comparing to autotrophic growth, mixotrophic cultivation with glucose supplementation led to a decrease of chlorophyll and fucoxanthin content in N. laevis, and an increase of biomass density and EPA yield. To further examine the metabolic barriers for fucoxanthin and EPA biosynthesis, comparative transcriptomic and metabolome analyses were conducted, with a focus on the genes related to carotenoids biosynthesis and fatty acid metabolism. The results indicated that phytoene desaturase (PDS) and zeta-carotene isomerase (ZISO) could be the rate-limiting enzymes in carotenoid biosynthesis. The transcription regulation of 3-ketoacyl-CoA synthase (KCS) and elongation of very long chain fatty acids protein (EVOVL) are important contributors associated with polyunsaturated fatty acids (PUFAs) accumulation. Furthermore, we also investigated the glucose-associated regulatory genes using weighted gene co-expression network analysis, and identified potential hub genes linked with cell cycle, carbohydrate metabolism, purine biosynthesis, and lipid metabolism. This study offers a high-quality transcriptome resource for N. laevis and provides a molecular framework for further metabolic engineering studies on fucoxanthin and EPA production.

Highlights

Diatoms are important producers in the aquatic systems, as they are estimated to undertake 20–25% of the global carbon fixation and contribute ~40% of net primary productions [1,2]
The cellular abundance of fucoxanthin was decreased in mixotrophic cells after 4-day culture with glucose (Figure 1B)
The decrease of both chlorophyll (Figure 1B) and fucoxanthin content indicates a general downregulation of the photosynthetic apparatus under glucose addition

Summary

Introduction

Diatoms are important producers in the aquatic systems, as they are estimated to undertake 20–25% of the global carbon fixation and contribute ~40% of net primary productions [1,2]. They play important roles in taking part in the biogeochemical cycling of silicon and carbon in the ecosystem [3]. Diatoms are important sources of bioactive compounds like fucoxanthin, polyunsaturated fatty acids (PUFAs), e.g., eicosapentaenoic acid (EPA), flavonoids, phenolic compounds, as well as lipid production for biofuels [4,5]. Chrysolaminarin (β-1,3-glucan), the principal storage polysaccharide in the diatom stored in

Methods

Results

Conclusion