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The spatial and temporal environmental conditions in the southern coastal waters of Korea (SCWK) as a complex area, which is influenced by both ocean currents and anthropogenic nutrient inputs, are highly variable. The impacts of environmental factors on the distribution of phytoplankton community structure in the SCWK remain unclear. Based on high-performance liquid chromatography (HPLC) analysis of a variety of photosynthetic pigments, spatial and temporal variations in phytoplankton community compositions were investigated in the SCWK. Cluster analysis, correlation analysis, and generalized additive models (GAMs) were used to explore the major phytoplankton groups and their response patterns to temperature, salinity, depth, and macronutrients. The results indicated that diatoms were the absolute dominant groups in the SCWK for all seasons, especially in cold seasons. Diatoms mainly concentrated at 1% light depths, while high chlorophyll-a concentrations (>3 µg/L) occurred at 100% and 30% light depths with good light conditions. Both clustering and correlation analyses showed that diatoms had a strong positive correlation with macronutrients such as dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP), and dissolved silica (DSi). The temperature and salinity discrepancy between surface and bottom layers in summer caused a strong water stratification resulting in blocking nutrient-rich bottom water upwelling and leading cyanobacteria to become the dominant groups at 100% and 30% light depths in summer. Consistently, the cyanobacteria were highly associated with high temperature and low salinity in the correlation analysis and GAM results. Compared with diatom-predominant sites, cryptophytes and diatom-dominated sites are characterized by higher average excess nitrate (ExN). Further research on the responses of small-sized prokaryotic phytoplankton especially cyanobacteria to environmental variations and their primary production contributions would warrant a better understanding of the SCWK ecosystem.

The relative importance of interannual environmental changes in shaping phytoplankton community structure remains unclear in the East China Sea (ECS), which is the largest marginal sea in the western North Pacific Ocean. Based on high-performance liquid chromatography (HPLC) analysis of a variety of photosynthetic pigments, we investigated spatiotemporal variations in the phytoplankton community in the northern East China Sea (NECS) from 2018 to 2020 to understand biomass and compositional responses to environmental conditions in a complex current system. Correlation heatmaps and generalized additive models (GAMs) were used to explore the variations in major phytoplankton groups and their relationships to temperature, salinity, depth, and nutrients. The results indicated that the phytoplankton community structure was significantly different between 2018/2019 and 2020. Under the conditions of high dissolved inorganic nitrogen (DIN) and low dissolved inorganic phosphate (DIP) concentrations in winter 2020, cryptophytes replaced diatoms as the dominant species and were observed for the first time in this study area. Dinoflagellates predominated throughout the euphotic zone in spring 2020, and statistical analysis showed that dinoflagellates tended to prevail at low DIP and high DIN conditions compared with diatoms. Summer was the only season with strong water stratification that reoccurred every year, and diatoms were mainly concentrated at nutrient-enriched 1% light depths in the summers of 2018/2019. However, a large amount of Changjiang River Diluted Water (CDW) from the surface and western part of the study area affected all sampling sites eastward to 126°E in 2020, allowing diatoms to be dominant at 100% and 30% light depths in the westernmost stations in the NECS. In autumn 2020, diatoms decreased significantly because of DIP-limited environmental conditions and were replaced by small phytoplankton. Under expected warming ocean scenarios with human-induced nutrient inputs, small phytoplankton will become dominant, while spring dinoflagellate blooms will occur more frequently in the NECS. International monitoring programs for marine ecosystems are currently needed in the ECS.

The novel cellobiohydrolase gene ctcel7 was identified from Chaetomium thermophilum, and its recombinant protein CtCel7, a member of glycoside hydrolase family 7, was heterologously expressed in Pichia pastoris and biochemically characterized. Compared with commercial hydrolases, purified CtCel7 exhibited superior bifunctional cellobiohydrolase and xylanase activities against microcrystalline cellulose and xylan, respectively, under optimal conditions of 60°C and pH 4.0. Moreover, CtCel7 displayed remarkable thermostability with over 90% residual activity after heat (60°C) treatment for 180 min. CtCel7 was insensitive to most detected cations and reagents and preferentially cleaved the β-1,4-glycosidic bond to generate oligosaccharides through the continuous saccharification of lignocellulosic substrates, which are crucial for various practical applications. Notably, the hydrolysis effect of a commercial cellulase cocktail on pretreated wheat straw was substantively improved by its combination with CtCel7. Taken together, these excellent properties distinguish CtCel7 as a robust candidate for the biotechnological production of biofuels and biobased chemicals.