Insights into Alexandrium minutum Nutrient Acquisition, Metabolism and Saxitoxin Biosynthesis through Comprehensive Transcriptome Survey

Abstract

The toxin-producing dinoflagellate Alexandrium minutum is responsible for the outbreaks of harmful algae bloom (HABs). It is a widely distributed species and is responsible for producing paralytic shellfish poisoning toxins. However, the information associated with the environmental adaptation pathway and toxin biosynthesis in this species is still lacking. Therefore, this study focuses on the functional characterization of A. minutum unigenes obtained from transcriptome sequencing using the Illumina Hiseq 4000 sequencing platform. A total of 58,802 (47.05%) unigenes were successfully annotated using public databases such as NCBI-Nr, UniprotKB, EggNOG, KEGG, InterPRO and Gene Ontology (GO). This study has successfully identified key features that enable A. minutum to adapt to the marine environment, including several carbon metabolic pathways, assimilation of various sources of nitrogen and phosphorus. A. minutum was found to encode homologues for several proteins involved in saxitoxin biosynthesis, including the first three proteins in the pathway of saxitoxin biosynthesis, namely sxtA, sxtG and sxtB. The comprehensive transcriptome analysis presented in this study represents a valuable resource for understanding the dinoflagellates molecular metabolic model regarding nutrient acquisition and biosynthesis of saxitoxin.

Nutrient Deficiencies Impact on the Cellular and Metabolic Responses of Saxitoxin Producing Alexandrium minutum: A Transcriptomic Perspective

“…RNA-seq datasets used throughout this study were obtained from our previous research. These data can be downloaded from the NCBI Sequence Read Archive (SRA) Database under the BioProject id: PRJNA914202 [ 16 ]. In brief, A. minutum cells were grown in nutrient-replete ES-DK media until they reached the exponential phase before being transferred using a 15 m mesh filter to new ES-DK media lacking nitrogen/phosphorus components to induce nitrogen/phosphorus limitation in A. minutum cultures ( Figure 6 ).…”

“…Then, the RNA was harvested from A. minutum cells that were starved of nitrogen and phosphorus for 72 h. A HACH DR2800 spectrophotometer was used to confirm the growth media’s lack of nitrogen/phosphorus. The complete annotation pipeline for A. minutum transcriptome was described in our previous study [ 16 ]. A complete annotation of A. minutum unigenes is available in Table S3 .…”

“…Our previous study described a comprehensive gene catalog for A. minutum that highlights various metabolic pathways and critical adaptations to the marine environment [ 16 ]. A. minutum might exhibit physiological adaptability in response to a variety of environmental challenges, including nutrition deprivation [ 8 , 9 , 17 , 18 ].…”

Environmental Factors Modulate Saxitoxins (STXs) Production in Toxic Dinoflagellate Alexandrium: An Updated Review of STXs and Synthesis Gene Aspects

“…In detail, STXs biosynthesis requires the use of additional C skeletons produced during photosynthesis, such as amino acids and acetate, as well as high-energy light intermediates, such as ATP and NADH/NADPH [108]. Such amino acids are produced during short periods of photo-assimilation [109], and this also requires incorporated NO 3 [110,111]. Therefore, the decrease in light intensity can suppress the fresh synthesis of amino acids and N assimilation [84], affecting growth and varied metabolisms, including the production of secondary metabolites.…”

Exploring potential polysaccharide utilization loci involved in the degradation of typical marine seaweed polysaccharides by Bacteroides thetaiotaomicron

“…The paired-end sequencing with a read length of 150 base pairs was conducted according to the manufacturer's guidelines for whole genome sequencing, utilizing the Illumina HiSeq 2500 sequencer on the Illumina HiSeq 2500 platform (San Diego, CA, United States), achieving a 100-fold sequencing depth. After the completion of Illumina sequencing, the raw data undergo a series of data analysis operations, including quality control, statistical analysis, genome assessment, and de novo assembly (Akbar et al, 2021;Dang et al, 2022).…”