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

ABSTRACT

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]AbbreviationsBP 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.