09:00 〜 09:15
[AOS17-01] Temporal changes in the composition of extracellular polymeric substances of diatoms and their potential link to cell lysis
キーワード：細胞外ポリマー物質、透明細胞外ポリマー粒子、クーマシーブリリアントブルー染色粒子、珪藻
Extracellular polymeric substances (EPS), a component of marine particles, include transparent exopolymer particles (TEP), made of acidic polysaccharides, and Coomassie Brilliant Blue-stained particles (CSP), containing proteinaceous materials. The ratio of proteins to carbohydrates (CSP/TEP ratio) has been suggested as a potential indicator of hydrophobicity, stickiness, aggregation efficiency, and sedimentation of EPS in seawater (Santschi et al., 2020). The concentrations of TEP and CSP in the ocean have been reported to be associated with phytoplankton blooms. TEP concentrations increase even after the bloom (Alldredge et al., 1995; Mari and Kiørboe, 1996; Engel, 2002; Engel et al., 2004), while CSP concentrations increase during the exponential growth phase of the bloom and decrease afterward (Cisternas-Novoa et al., 2015). Therefore, the CSP/TEP ratio is expected to peak during the exponential growth phase of phytoplankton blooms. However, bacteria, viruses, and zooplankton also influence EPS production by phytoplankton (Gärdes et al., 2012; Møller, 2007; Yamada et al., 2018), and the CSP/TEP ratio of EPS produced by phytoplankton remains largely unexplored in marine environments.
In this study, we investigated the CSP/TEP ratio of EPS produced by two diatom species, Thalassiosira weissflogii and Thalassiosira pseudonana, under different nutrient conditions. These diatoms were pure-cultured for four weeks, and EPS concentrations and the CSP/TEP ratio were measured twice a week. TEP and CSP concentrations increased over time, ranging from 1.1 to 30.3 GXeq. mg L-1 and 0.1 to 21.3 BSAeq. mg L-1, respectively. Although the CSP/TEP ratio roughly increased over time, ranging from 0.1 to 1.0, it peaked at 2 weeks and 3.5 weeks for T. weissflogii under different nutrient levels, while for T. pseudonana, the peak occurred at 3.5 weeks, regardless of nutrient conditions. Microscopic observations and cell counts revealed that cell abundance peaked during weeks 3–4, with cell lysis becoming significant during weeks 2–3. This suggests that the rise in CSP/TEP ratio is linked to cell lysis. Our results highlight that EPS characteristics change depending on diatom growth stages, potentially influencing marine biogeochemical cycles through particle aggregation and sedimentation processes.
In this study, we investigated the CSP/TEP ratio of EPS produced by two diatom species, Thalassiosira weissflogii and Thalassiosira pseudonana, under different nutrient conditions. These diatoms were pure-cultured for four weeks, and EPS concentrations and the CSP/TEP ratio were measured twice a week. TEP and CSP concentrations increased over time, ranging from 1.1 to 30.3 GXeq. mg L-1 and 0.1 to 21.3 BSAeq. mg L-1, respectively. Although the CSP/TEP ratio roughly increased over time, ranging from 0.1 to 1.0, it peaked at 2 weeks and 3.5 weeks for T. weissflogii under different nutrient levels, while for T. pseudonana, the peak occurred at 3.5 weeks, regardless of nutrient conditions. Microscopic observations and cell counts revealed that cell abundance peaked during weeks 3–4, with cell lysis becoming significant during weeks 2–3. This suggests that the rise in CSP/TEP ratio is linked to cell lysis. Our results highlight that EPS characteristics change depending on diatom growth stages, potentially influencing marine biogeochemical cycles through particle aggregation and sedimentation processes.