Cloning and characterization of selenoprotein thioredoxin reductase gene in Haematococcus pluvialis

Systematic Analysis of Genes Related to Selenium Bioaccumulation in Microalgae: A Review

Se is one of the essential nutrients for human health and animal growth; it participates in various physiological functions, such as antioxidant and immune response and metabolism. Se deficiency is related in the animal industry to poor production performance and the appearance of health problems in humans. Therefore, interest has arisen in producing fortified foods, nutritional supplements, and animal feed products enriched with Se. A sustainable strategy for bio-based products enriched with Se is microalgae. These are characterized by the ability to bioaccumulate inorganic Se and metabolize it into organic Se for product formulations of industrial interest. Although there are some reports on Se bioaccumulation, further exploration is needed to understand the effects of Se bioaccumulation in microalgae. Therefore, this article presents a systematic review of the genes or groups of genes that trigger biological responses associated with the metabolization of Se in microalgae. A total of 54,541 genes related to Se metabolization distributed in 160 different classes were found. Similarly, trends were identified through bibliometric networks on strains of greatest interest, bioproducts, and scientific production.

Characterization of a new selenoprotein methionine sulfoxide reductase from Haematococcus pluvialis and its antioxidant activity in response to high light intensity, hydrogen peroxide, glyphosate, and cadmium exposure

Selenium incorporates into selenocysteine (Sec) which is a key component of selenoproteins implicated in antioxidant defense and redox homeostasis. Methionine sulfoxide reductases (Msr) play crucial roles in cellular defense against environmental stress. Whereas mammals have the MsrB selenoprotein form, unicellular organisms have MsrA. The Sec residue at the conserved catalytic sites of selenoprotein MsrA confers a metabolic advantage over the non-selenoprotein type MsrA. In the present study, the novel selenoprotein HpMsrA from Haematococcus pluvialis was cloned by the rapid amplification of cDNA ends and transformed into the model green alga Chlamydomonas reinhardtii. Alignment of homologs revealed the presence of the conserved catalytic domain GUFW and showed that the HpMsrA protein comprises Sec (U) at the N-terminus but no recycled Cys at the C-terminus. We studied the response of HpMsrA expression to selenite, high light intensity, hydrogen peroxide, cadmium nitrate, and glyphosate exposure via real-time quantitative PCR and enzyme activity analysis. The results demonstrated that HpMsrA protects cellular proteins against oxidative and environmental stressors. Compared with wild type C. reinhardtii, the transformant exhibited a superior antioxidant ability. The discoveries made herein shed light on the antioxidant physiology and environmental stress resistance mechanisms of the selenoproteins in microalgae. This information may aid in conducting environmental risk assessments of aquatic ecosystems involving microalgae known to respond rapidly and quantitatively to abiotic stress factors promoting excessive reactive oxygen species generation.

Sequencing and Characterization of Novel PII Signaling Protein Gene in Microalga Haematococcus pluvialis

The PII signaling protein is a key protein for controlling nitrogen assimilatory reactions in most organisms, but little information is reported on PII proteins of green microalga Haematococcus pluvialis. Since H. pluvialis cells can produce a large amount of astaxanthin upon nitrogen starvation, its PII protein may represent an important factor on elevated production of Haematococcus astaxanthin. This study identified and isolated the coding gene (HpGLB1) from this microalga. The full-length of HpGLB1 was 1222 bp, including 621 bp coding sequence (CDS), 103 bp 5' untranslated region (5' UTR), and 498 bp 3' untranslated region (3' UTR). The CDS could encode a protein with 206 amino acids (HpPII). Its calculated molecular weight (Mw) was 22.4 kDa and the theoretical isoelectric point was 9.53. When H. pluvialis cells were exposed to nitrogen starvation, the HpGLB1 expression was increased 2.46 times in 48 h, concomitant with the raise of astaxanthin content. This study also used phylogenetic analysis to prove that HpPII was homogeneous to the PII proteins of other green microalgae. The results formed a fundamental basis for the future study on HpPII, for its potential physiological function in Haematococcus astaxanthin biosysthesis.

A Novel Organic Electrochemical Transistor-Based Platform for Monitoring the Senescent Green Vegetative Phase of Haematococcus pluvialis Cells

The freshwater unicellular microalga Haematococcus pluvialis (H. pluvialis) has gained increasing attention because of its high-value metabolite astaxanthin, a super anti-oxidant. For the maximum astaxanthin production, a key problem is how to determine the senescent green vegetative phase of H. pluvialis cells to apply the astaxanthin production inducers. The conventional methods are time-consuming and laborious. In this study, a novel platform based on organic electrochemical transistor (OECT) was produced. A significant channel current change of OECTs caused by settled H. pluvialis cells on the poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) film was recorded commencing from 75 min and a stationary stage was achieved at 120 min after the combined treatment of blue light irradiation and sodium bicarbonate solution additives, which indicate the onset and maturation of the senescent green vegetative phase, respectively. Therefore, the appropriate time point (120 min after sample loading) to apply astaxanthin production inducers was determined by as-fabricated OECTs. This work may assist to develop a real-time biosensor to indicate the appropriate time to apply inducers for a maximum astaxanthin production of H. pluvialis cells.

Effects of selenite on green microalga Haematococcus pluvialis: Bioaccumulation of selenium and enhancement of astaxanthin production

Algae are at a low trophic level and play a crucial role in aquatic food webs. They can uptake and accumulate the trace element selenium (Se), which can be either essential or toxic to algal growth depending on the dosage and species. Se toxicity and algae resistance varied across different organisms. In order to investigate the effects of Se on the unicellular green alga Haematococcus pluvialis, an important industrial resource for natural astaxanthin, the algal growth rate, chlorophyll content, and fluorescence parameters were derived from experimental treatment with different concentrations of selenite. The results showed that the EC₅₀ for the algal growth rate was 24mg/L, and that a low dosage of selenite (3mg/L) may not hinder H. pluvialis cell growth, but selenite at levels higher than 13mg/L do restrain cell growth. Bioaccumulation experiments showed that H. pluvialis accumulated up to 646μg/g total Se and 380μg/g organic Se, dry weight. However, treatment with high concentrations of selenite significantly increased intracellular hydrogen peroxide levels, antioxidant enzyme activity, and the production of astaxanthin, suggesting that Se bioaccumulation might be toxic to H. pluvialis.