Ho-Sung Yoon’s research while affiliated with Kyungpook National University and other places

The increasing demand for sustainable and eco-friendly energy sources has intensified research into alternative biofuel feedstocks. Microalgae, recognized for their rapid growth and production of high-value products, have emerged as promising candidates for third-generation biofuels. This study evaluates the potential of Protosiphon botryoides KNUA219, a microalga isolated from Dokdo Island, South Korea, as a biodiesel feedstock. Molecular and morphological analyses confirmed its identity, while growth experiments demonstrated its species-specific physiological characteristics, including an optimal pH range of 5−7, limited salinity tolerance, and high biomass productivity. Biochemical analysis revealed significant levels of carbohydrates (30.42 ± 1.65%), proteins (26.18 ± 1.14%), and lipids (14.86 ± 0.33%) in P. botryoides KNUA219, with glucose and galactose as the dominant monosaccharides. Fatty acid methyl ester profiling identified a lipid composition consisting of saturated (20.54%), monounsaturated (19.03%), and polyunsaturated fatty acids (42.65%), with palmitic, oleic, and linolenic acids as key components. Biodiesel quality assessments indicated compliance with critical standards for cetane number and cold filter plugging point, although optimization was required for iodine value and density. Proximate and ultimate analyses revealed favorable energy properties, including a high volatile matter content (88.94 ± 0.33%) and a calorific value of 23.11 ± 0.11 MJ/kg. These findings establish P. botryoides KNUA219 as a promising and sustainable resource for biodiesel production, while highlighting its potential for broader industrial applicability.

The management of swine wastewater (SW) presents significant environmental challenges, requiring solutions that combine effective treatment with resource recovery. This study highlights the dual role of microalgae in wastewater remediation and bioenergy production. H. rubescens KNUA214 was cultivated in media containing varying concentrations of diluted swine wastewater (DSW; 0%, 25%, 50%, and 100%). Cultivating with Blue Green-11 (BG-11) medium + 50% DSW maximized biomass growth, the chlorophyll content, and carotenoid production. Nutrient removal efficiency in 100% DSW over 8 days demonstrated reductions of 59.3% in total nitrogen, 67.7% in ammonia nitrogen, and 40.7% in total phosphorus, confirming the species’ capacity for effective wastewater treatment. The carotenoid analysis using HPLC revealed that astaxanthin, lutein, canthaxanthin, and beta-carotene exhibited the highest levels in BG-11 + 50% DSW. Furthermore, the biomass analyses confirmed its potential for bioenergy applications, with high calorific values and significant polyunsaturated fatty acid concentrations, enhancing its utility for bioenergy and biolubricant production. These findings position H. rubescens KNUA214 as an effective resource for integrating SW management with the sustainable production of high-value biochemicals, offering environmental and economic benefits.

The study of microalgal communities is critical for understanding aquatic ecosystems. These communities primarily comprise diatoms (Heterokontophyta), with two methods commonly used to study them: Microscopy and metabarcoding. However, these two methods often deliver different results; thus, their suitability for analyzing diatom communities is frequently debated and evaluated. This study used these two methods to analyze the diatom communities in identical water samples and compare the results. The taxonomy of the species constituting the diatom communities was confirmed, and both methods showed that species belonging to the orders Bacillariales and Naviculales (class Bacillariophyceae) are the most diverse. In the lower taxonomic levels (family, genus, and species), microscopy tended to show a bias toward detecting diatom species (Nitzschia frustulum, Nitzschia inconspicua, Nitzschia intermedia, Navicula gregaria, Navicula perminuta, Navicula recens, Navicula sp.) belonging to the Bacillariaceae and Naviculaceae families. The results of the two methods differed in identifying diatom species in the communities and analyzing their structural characteristics. These results are consistent with the fact that diatoms belonging to the genera Nitzschia and Navicula are abundant in the communities; furthermore, only the Illumina MiSeq data showed the abundance of the Melosira and Entomoneis genera. The results obtained from microscopy were superior to those of Illumina MiSeq regarding species-level identification. Based on the results obtained via microscopy and Illumina MiSeq, it was revealed that neither method is perfect and that each has clear strengths and weaknesses. Therefore, to analyze diatom communities effectively and accurately, these two methods should be combined. Supplementary Information The online version contains supplementary material available at 10.1007/s00248-024-02396-x.

The study of microalgal communities is critical for understanding aquatic ecosystems. These communities are primarily composed of diatoms (Bacillariophyta), and two methods are commonly used to study them: microscopy and Illumina MiSeq. These two methods are distinct, and their differences are reflected in the results they yield. Thus, their suitability for analyzing diatom communities is often debated and evaluated. In this study, these two methods were used to analyze the diatom communities in the same water samples, and the results obtained were compared. The taxonomy of the species constituting the diatom communities was confirmed, and both methods showed that the species belonging to the Bacillariales and Naviculales orders (class Bacillariophyceae) are diverse. However, at the lower taxonomic levels (family, genus, and species), microscopy tended to show a bias toward detecting diatom species belonging to the Bacillariaceae and Naviculaceae families. The results obtained from the two methods differed in terms of the identification of each diatom present in the communities and the analysis of their structural characteristics. These results are consistent with the fact that diatoms belonging to the Nitzschia and Navicula genera are abundant in the communities, furthermore, only the Illumina MiSeq showed the abundance of the Melosira , Entomonis , and Amphiprora genera. Although the results obtained from microscopy tended to be biased, they were superior to those of Illumina MiSeq regarding species-level identification. Based on the results obtained via microscopy and Illumina MiSeq, it was revealed that neither method is perfect and that each has clear strengths and weaknesses. Therefore, for the effective and accurate analysis of diatom communities, it is desirable to combine the two methods.

Sargassum horneri which seasonally enters East Asian waters frequently leads to negative economic consequences despite its ecological importance. It damages vessel engines and fishing gear and releases hydrogen sulfide and ammonia as it rots. Traditionally, seaweed drifts have been used as fertilizers in certain coastal areas in Korea, but there have been no scientific reports regarding this kind of application of seaweeds. Hence, this study attempted to use Sargassum biomass as a soil amendment by monitoring soil properties and microbiome changes and soybean growth in Sargassum-added soil. Our results suggested that the addition of S. horneri biomass to soil improved soil physicochemical properties such as cation exchange capacity (CEC) levels that represents soil’s capacity to retain cations leading to more soil fertility. As (max. value 24.97 mg kg⁻¹) and Cd (max. value 0.58 mg kg⁻¹) concentration increases were notable in the soil, but all the metal levels were well below the Korean soil quality standards for agricultural uses except for As (25 mg kg⁻¹ limit) which is just a little lower than the limit. Diversity index results indicated that fungal and bacterial diversities were affected by the amount of Sargassum added. Our study demonstrated that seasonal drifts of S. horneri could be used as an excellent soil amendment. Moreover, Glycine max (L.) Merr. cultivation experiments suggested that 4% of S. horneri was the optimal amount to enhance soybean growth in agricultural practice.

Global water scarcity increased the demand for clean water, leading to attention on microalgae-based biological treatment for wastewater due to economic feasibility and sustainable biomass applications. This study isolated indigenous microalga Coelastrella sp. KNUA068 from a wastewater treatment plant, observed its admissible growth rate in diluted cattle wastewater (DCW), and used it for wastewater treatment analysis. The microalga showed high growth rates in indoor and outdoor cultivation with 100% DCW. In addition, the ammonia nitrogen and nitrate nitrogen removal rates of the microalga were 69.97 and 60.35%, respectively, in indoor cultivation, and 50.63 and 67.20%, respectively, in outdoor cultivation. Carotenoid content analysis revealed lutein as the highest productivity carotenoid, and zeaxanthin production was higher in outdoor cultivation. The biomass exhibited suitable biodiesel quality with a cetane number of 50.8 for high-quality biodiesel production. Coelastrella sp. KNUA068 demonstrates potential for bioenergy feedstock, carotenoid production, and wastewater treatment.

The prokaryotic microalga Limnothrix redekei KNUA012 isolated from a freshwater bloom sample from Lake Hapcheon, Hapcheon-gun, South Korea, was investigated for its potential as a biofuel feedstock. Microalgae produce straight-chain alkanes/alkenes from acyl carrier protein-linked fatty acyls via aldehyde decarbonylase (AD; EC 1.2.1.3), which can convert aldehyde intermediates into various biofuel precursors, such as alkanes and free fatty acids. In L. redekei KNUA012, long-chain ADs can convert fatty aldehyde intermediates into alkanes. After heterologous AD expression in Escherichia coli (pET28-AD), we identified an AD in L. redekei KNUA012 that can synthesize various alkanes, such as pentadecane (C 15 H 32 ), 8-heptadecene (C 17 H 34 ), and heptadecane (C 17 H 36 ). These alkanes can be directly used as fuels without transesterification. Biodiesel constituents including dodecanoic acid (C 13 H 26 O 2 ), tetradecanoic acid (C 15 H 30 O 2 ), 9-hexa decenoic acid (C 17 H 32 O 2 ), palmitoleic acid (C 17 H 32 O 2 ), hexadecanoic acid (C 17 H 34 O 2 ), 9-octadecenoic acid (C 19 H 36 O 2 ), and octadecanoic acid (C 19 H 38 O 2 ) are produced by L. redekei KNUA012 as the major fatty acids. Our findings suggest that Korean domestic L. redekei KNUA012 is a promising resource for microalgae-based biofuels and biofuel feedstock.

Various abiotic stress factors, such as high temperatures and salinity, have a significant impact on the development and growth of crop plants and ultimately impact crop yield. Previous studies have reported that overexpression of heat-shock-protein (HSP) genes in transgenic plants can enhance stress tolerance under controlled conditions in laboratories and greenhouses. Despite the significance of multiple environmental stressors on plants in natural paddy fields, there is still a lack of research regarding the contribution of HSP genes to stress tolerance and crop yield. In this study, we cloned and characterized the function of OsHSP 17.9, an HSP gene from Oryza sativa, in rice plants grown under diverse conditions. Our results showed that overexpressing OsHSP 17.9 in rice plants enhanced the activity of antioxidant enzymes under high-temperature and salinity stresses. Moreover, transgenic rice plants overexpressing OsHSP 17.9 exhibited significantly improved adaptability after transplantation from greenhouses to natural paddy fields. In particular, OsHSP 17.9-overexpressing transgenic rice plants established improved agronomic traits and increased grain yields even under unfavorable natural-paddy-field conditions. These results suggest that OsHSP 17.9 transgenic plants can be a promising strategy for cultivating crops in adverse environmental conditions.