The cadmium tolerance and bioaccumulation mechanism of Tetratostichococcus sp. P1: insight from transcriptomics analysis.

Cadmium (Cd) has become a severe issue in relatively low concentration and attracts expert attention due to its toxicity, accumulation, and biomagnification in living organisms. Cd does not have a biological role and causes serious health issues. Therefore, Cd pollutants should be reduced and removed from the environment. Microalgae have great potential for Cd absorption for waste treatment since they are more environmentally friendly than existing treatment methods and have strong metal sorption selectivity. This study evaluated the tolerance and ability of the microalga Tetratostichococcus sp. P1 to remove Cd ions under acidic conditions and reveal mechanisms based on transcriptomics analysis. The results showed that Tetratostichococcus sp. P1 had a high Cd tolerance that survived under the presence of Cd up to 100 µM, and IC50, the half-maximal inhibitory concentration value, was 57.0 µM, calculated from the change in growth rate based on the chlorophyll content. Long-term Cd exposure affected the algal morphology and photosynthetic pigments of the alga. Tetratostichococcus sp. P1 removed Cd with a maximum uptake of 1.55 mg g-1 dry weight. Transcriptomic analysis revealed the upregulation of the expression of genes related to metal binding, such as metallothionein. Group A, Group B transporters and glutathione, were also found upregulated. While the downregulation of the genes were related to photosynthesis, mitochondria electron transport, ABC-2 transporter, polysaccharide metabolic process, and cell division. This research is the first study on heavy metal bioremediation using Tetratostichococcus sp. P1 and provides a new potential microalga strain for heavy metal removal in wastewater.[Figure: see text]Abbreviations:BP: Biological process; bZIP: Basic Leucine Zipper; CC: Cellular component; ccc1: Ca (II)-sensitive cross complementary 1; Cd: Cadmium; CDF: Cation diffusion facilitator; Chl: Chlorophyll; CTR: Cu TRansporter families; DAGs: Directed acyclic graphs; DEGs: Differentially expressed genes; DVR: Divinyl chlorophyllide, an 8-vinyl-reductase; FPN: FerroportinN; FTIR: Fourier transform infrared; FTR: Fe TRansporter; GO: Gene Ontology; IC50: Growth half maximal inhibitory concentration; ICP: Inductively coupled plasma; MF: molecular function; NRAMPs: Natural resistance-associated aacrophage proteins; OD: Optical density; RPKM: Reads Per Kilobase of Exon Per Million Reads Mapped; VIT1: Vacuolar iron transporter 1 families; ZIPs: Zrt-, Irt-like proteins.

Enhancement of Squalene Production by Constitutive Expression of the 3-Hydroxy-3-Methylglutaryl-CoA Reductase in Aurantiochytrium sp. 18W-13a.

Squalene has a wide range of applications in the industry sectors of dietary supplements, cosmetics, immunization, and pharmaceuticals. Yet, suitable organisms as the source of squalene are limited. It is reported that the thraustochytrid Aurantiochytrium sp. strain 18W-13a can accumulate high content of squalene. However, squalene production in this organism is fluctuated under various conditions and is not yet optimized for commercialization. In this organism, the mevalonate pathway supplies isopentenyl pyrophosphate, the initial substrate for squalene production. In this pathway, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) is the rate-limiting enzyme. We found that the HMGR activity had a strong positive correlation with the squalene contents in the strain. We constitutively expressed the HMGR in this organism and found that the transformant showed increased and stable production of squalene as well as carotenoids and biomass. These results clearly indicated that the HMGR expression is the bottleneck of squalene synthesis in Aurantiochytrium sp.