No abstract

We developed a process for one-pot CO2 conversion and utilization based on simple conversion of CO2 to bicarbonate at ambient temperature with no energy input, by using the cross-linking-based composites of carboxylated polyaniline nanofibers (cPANFs) and carbonic anhydrase. Carbonic anhydrase was immobilized on cPANFs via the approach of magnetically separable enzyme precipitate coatings (Mag-EPC), which consists of covalent enzyme attachment, enzyme precipitation, and cross-linking with amine-functionalized magnetic nanoparticles. Mag-EPC showed a half-life of 236 days under shaking, even resistance to 70% ethanol sterilization, and recyclability via facile magnetic separation. For one-pot CO2 conversion and utilization, Mag-EPC was used to accelerate the growth of microalga by supplying bicarbonate from CO2, representing 1.8-fold increase of cell concentration when compared to the control sample. After two repeated uses via simple magnetic separation, the cell concentration with Mag-EPC was maintained as high as the first cycle. This one-pot CO2 conversion and utilization is an alternative as well as complementary process to adsorption-based CO2 capture and storage as an environmentally friendly approach, demanding no energy input based on the effective action of the stabilized enzyme system.

Zeaxanthin is a xanthophyll pigment that is regarded as one of the best carotenoids for the prevention and treatment of degenerative diseases. In the worldwide natural products market, consumers prefer pigments that have been produced from biological sources. In this study, a Dunaliella tertiolecta strain that has 10–15% higher cellular zeaxanthin content than the parent strain (zea1), was obtained by random mutagenesis using ethyl methanesulfonate (EMS) as a mutagen. This mutant, mp3, was grown under various salinities and light intensities to optimize culture conditions for zeaxanthin production. The highest cellular zeaxanthin content was observed at 1.5 M NaCl and 65–85 μmol photons·m−2·s−1, and the highest daily zeaxanthin productivity was observed at 0.6 M NaCl and 140–160 μmol photons·m−2·s−1. The maximal yield of zeaxanthin from mp3 in fed-batch culture was 8 mg·L−1, which was obtained at 0.6 M NaCl and 140–160 μmol photons·m−2·s−1. These results suggest that random mutagenesis with EMS is useful for generating D. tertiolecta strains with increased zeaxanthin content, and also suggest optimal culture conditions for the enhancement of biomass and zeaxanthin production by the zeaxanthin accumulating mutant strains.

Lectins have the ability to bind specific carbohydrates and they have potential applications as medical and pharmacological agents. The unique structure and usefulness of red algal lectin have been reported, but these lectins are limited to a few marine algal groups. In this study, a novel mannose-binding lectin from Grateloupia chiangii (G. chiangii lectin, GCL) was purified using antiviral screens and affinity chromatography. We characterized the molecular weight, agglutination activity, hemagglutination activity, and heat stability of GCL. To determine the carbohydrate specificity, a glycan microarray was performed. GCL showed strong binding affinity for Maltohexaose-β-Sp1 and Maltoheptaose-β-Sp1 with weak affinity for other monosaccharides and preferred binding to high-mannan structures. The N-terminal sequence and peptide sequence of GCL were determined using an Edman degradation method and LC-MS/MS, and the cDNA and peptide sequences were deduced. GCL was shown to consist of 231 amino acids (24.9 kDa) and the N-terminus methionine was eliminated after translation. GCL possessed a tandem repeat structure of six domains, similar to the other red algal lectins. The mannose binding properties and tandem repeat structure of GCL may confer it the potential to act as an antiviral agent for protection against viral infection.

Carbonic anhydrases convert CO2 to bicarbonate at a high turnover rate up to 106 s–1, but their actual applications in CO2 conversion processes are hampered by their poor stability. This study reports highly loaded and stabilized bovine carbonic anhydrase (bCA) upon being immobilized onto electrospun polymer nanofibers in the form of enzyme precipitate coating (EPC). The EPC protocol, consisting of enzyme covalent attachment, precipitation, and cross-linking, maintained 65.3% of initial activity even after being incubated in aqueous solution at room temperature under shaking at 200 rpm for 868 days. EPC also showed strong resistance to the treatment of the metal chelation agent, ethylenediaminetetraacetic acid, and molecular dynamic simulation was carried out to elucidate the prevention of metal leaching from the active site of bCA upon being cross-linked in the form of EPC. Highly stable EPC with high bCA loading was employed for the conversion of bubbling CO2 to bicarbonate, and the bicarbonate solution was utilized as a carbon source for expedited microalgae growth in a separate bioreactor. The addition of EPC in the bubbling CO2 reactor resulted in 134 and 231% accelerated microalgae growths compared to the controls with and without 25 mM sodium bicarbonate, respectively. EPC with high enzyme loading and unprecedentedly successful stabilization of enzyme stability has a great potential to be used for the development of various enzyme-mediated CO2 conversion and utilization technologies.