While phytoplankton are a major component of coastal ecosystems and experience a wide range of oxygen conditions, the survival and physiological responses of common phytoplankton species under hypoxia remain insufficiently understood. To explore these effects, cell densities of the two dinoflagellate species Prorocentrum triestinum and Amphidinium carterae, and the two diatom species Cylindrotheca closterium and Chaetoceros curvisetus-isolated from waters with a dissolved oxygen (DO) concentration of 1.5 mg O-2 L-1-were measured under target DO concentrations of 0.5, 1.0, 1.5, 4.0, and >7.0 mg O-2 L-1. Using these data, the growth rate, net photosynthesis rate, and dark respiration rate of each species were determined. While A. carterae, Cy. closterium, and Ch. curvisetus survived at all tested DO concentrations, P. triestinum survived only at >= 1.0 mg O-2 L-1. The two dinoflagellate species examined here, which possess active swimming ability, exhibited the highest growth rates at >7.0 mg O-2 L-1, whereas the two diatom species examined here showed peak growth rate at 1.5 mg O-2 L-1. Net photosynthesis rates of all four species peaked at 1.5 mg O-2 L-1, while dark respiration rates were highest at >7.0 mg O-2 L-1. These findings suggest that although these phytoplankton species can grow under hypoxic conditions, dinoflagellate species achieve maximal growth at higher oxygen concentrations, possibly due to the energetic demands of motility. This study provides a useful basis for understanding species-specific responses of phytoplankton to varying oxygen conditions in coastal environments.
Prasiola japonica is a freshwater green alga distributed in Northeast Asia. This study investigated the effects of 70% ethanol extract of P. japonica (Pj-EE) under testosterone-induced hair loss conditions using C57BL/6 mice and human dermal papilla (HDP) cells. Topical application of Pj-EE promoted hair regrowth, increased hair length, and enhanced follicular density and activity in vivo. Pj-EE treatment also partially restored hair type distribution by reducing the proportion of zigzag hairs and increasing guard and awl hairs. Although these effects were less pronounced than those observed with minoxidil, consistent improvements were detected across multiple parameters. Mechanistic studies showed that Pj-EE inhibited 5 alpha-reductase activity and reduced dihydrotestosterone (DHT) production in HDP cells, accompanied by downregulation of androgen receptor expression. Additionally, Pj-EE decreased proapoptotic Bax levels while increasing proliferation-associated markers (Ki67 and proliferating cell nuclear antigen) and the anti-apoptotic protein Bcl-2 in a dose-dependent manner. Functionally, Pj-EE enhanced HDP cell proliferation and migration and attenuated testosterone-induced apoptotic responses, indicating improved follicular cell viability under androgen-stimulated conditions. High-performance liquid chromatography analysis based on comparison with an authentic phytol standard identified phytol as a representative constituent of Pj-EE, and its high abundance was associated with 5 alpha-reductase inhibitory activity. Collectively, these findings suggest that Pj-EE may attenuate androgen-responsive hair loss conditions by modulating 5 alpha-reductase/DHT signaling and supporting follicular cell proliferation and survival in a testosterone-induced model.
While gamma-aminobutyric acid (GABA) promotes nutrient accumulation in green microalgae, its effects on marine diatoms-critical aquaculture feed-remain understudied. Understanding the physiological response of diatoms to exogenous GABA is vital for optimizing high-quality feed production. In this study, we investigated the impact of GABA on diatom growth, photosynthetic performance, proximate composition (lipids, proteins, carbohydrates, and fatty acids), and oxidative stress markers of two commonly used feed diatoms Phaeodactylum tricornutum and Chaetoceros muelleri. GABA effects were species-specific: low doses (0.2-1.0 pmol cell-1) inhibited P. tricornutum at the exponential onset, while C. muelleri remained resilient to higher doses (1.5-16.2 pmol cell-1). Notably, this resilience in C. muelleri shifted to growth promotion when GABA was applied at the late stage, demonstrating clear stagedependency. In P. tricornutum, supplementation with 0.2-1.0 pmol cell-1 GABA triggered a significant accumulation of cellular carbohydrates, proteins, and lipids accompanied by a broad-spectrum increase in various cellular fatty acid concentrations including polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid and docosahexaenoic acid, important PUFAs. Notably, 1.0 pmol cell-1 GABA induced a three-fold increase in carbohydrate and lipid levels over the control. GABA triggered significant oxidative stress and photosynthetic inhibition in P. tricornutum in a dose-dependent manner, while C. muelleri exhibited high physiological tolerance with no marked changes in reactive oxygen species and superoxide dismutase or photosynthetic efficiency. A two-stage cultivation strategy involving initial biomass maximization and subsequent GABA-induced nutrient enrichment can be effectively utilized to biofortify P. tricornutum for use as aquaculture feed.
Zeaxanthin epoxidase (ZEP) plays a central role in carotenoid metabolism, but its evolution and function in red algae remain unclear. Here, we comprehensively identified ZEP homologs across red algal lineages through phylogenetic reconstruction, conserved motif analysis, structural comparison, and branch-specific selection pressure analyses to uncover adaptive evolutionary patterns. The ZEP homolog from Pyropia haitanensis (PhZEP) was selected for functional characterization, including promoter cis-element analysis, heterologous expression, in vitro enzymatic assays, and expression profiling under high light and desiccation-rehydration stress. Thirteen ZEP homologs were identified and clustered into three clades, indicating early divergence and a cyanobacterial origin. Lineage-specific structural divergence and purifying selection with relaxed constraints in Bangiophyceae were observed. Recombinant PhZEP specifically converted zeaxanthin to antheraxanthin, but not further to violaxanthin. PhZEP expression was moderately induced by high light and strongly upregulated during desiccation, peaking at 9.52-fold at 4.8% relative water content. These results demonstrate that PhZEP exhibits specific zeaxanthin epoxidase activity and may be associated with abiotic stress responses, providing insights into carotenoid pathway evolution and photoprotection strategies in red algae.
Dinoflagellate harbors diverse associated bacterial communities (ABCs) that play crucial roles in host physiology and ecological interactions. Coolia malayensis is a benthic dinoflagellate distributed from temperate to tropical regions. Despite growing knowledge about the morphology, distribution, and toxicity of C. malayensis, little is known about its associated bacteria, particularly under changing environmental conditions. Given that climate change alters microbial interactions through temperature shifts, this study investigated the composition, diversity, and dynamics of ABCs across four C. malayensis strains, under varying temperatures and growth time. Despite differences in strain origin, a stable core microbiome, comprising Alteromonas, Marinobacter, Muricauda, and Ruegeria, was consistently observed, suggesting these taxa are functionally important members of the ABC. However, strain-specific differences and temperature-driven shifts were also detected, especially among low-abundance bacterial taxa. Negative interactions among abundant amplicon sequence variants, such as those between Ruegeria and Muricauda, and between Alteromonas and Marinobacter, were conserved across conditions, suggesting stable patterns of co-occurrence. Functional predictions and Kyoto Encyclopedia of Genes and Genomes pathway analysis suggested potential involvement of ABCs in chemoheterotrophy, fermentation, hydrocarbon degradation, energy metabolism, and the metabolism of cofactors and vitamins, implying potential diverse metabolic exchanges between the bacteria and C. malayensis. These findings highlight both the ecological stability and environmental sensitivity of C. malayensis culture-associated microbiomes, with important implications for host health and ecosystem dynamics under climate change.
