College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China; Jiangsu Provincial Key Lab for Organic Solid Waste Utilization, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
Ecotoxicol Environ Saf. 2019 Jun 15;174:484-490. doi: 10.1016/j.ecoenv.2019.03.004. Epub 2019 Mar 8.
Microorganisms have been widely applied to heavy metal adsorption due to their strong secretion of extracellular polymeric substances (EPS). This study explored the responses of Rhodotorula mucilaginosa (R1, a red yeast with substantial EPS supply) under Pb stress. The maximum sorption of Pb cations by R1 was ~650 mg/L. In particular, despite the declined microbial biomass, the total Pb sorption after incubation was actually elevated in the solution with high Pb concentration. At 0-1000 mg/L Pb(NO) level, the longitudinal sizes of the yeast capsules increased from 2.04 to 2.90 µm. At 1500 mg/L, however, the survived yeast started to lose the membrane integrity of the cells. Meanwhile, the percentages of organic carbon contents of EPS decreased from 40% to 33% when the Pb(NO) concentration raised to 2500 mg/L, confirming the incorporation of Pb cations into the fungal EPS during the sorption. For the survived R1 cells, function of polysaccharides to resist Pb toxicity only worked at extremely high Pb(NO) levels (>= 1500 mg/L). In contrast, proteins showed continuously enhanced ability to resist Pb toxicity, consistent with their increasing content (per cell) in the EPS. Moreover, ATR-IR spectra showed that the intensity of amide II peak at 1540 cm was significantly increased, indicating elevated glutathione (GSH) in EPS. This suggested that GSH could be the critical Pb-binding component in EPS proteins. This study hence elucidated roles of polysaccharides and proteins in EPS under the toxicity caused by heavy metals.
微生物由于其强烈分泌细胞外聚合物（EPS）而被广泛应用于重金属吸附。本研究探讨了 Rhodotorula mucilaginosa（R1，一种具有大量 EPS 供应的红酵母）在 Pb 胁迫下的反应。R1 对 Pb 阳离子的最大吸附量约为 650mg/L。特别是，尽管微生物生物量下降，但在高 Pb 浓度的溶液中，孵育后总的 Pb 吸附量实际上增加了。在 0-1000mg/L Pb(NO)水平下，酵母胶囊的纵向尺寸从 2.04µm 增加到 2.90µm。然而，在 1500mg/L 时，存活的酵母开始失去细胞的膜完整性。同时，当 Pb(NO)浓度升高到 2500mg/L 时，EPS 中有机碳含量的百分比从 40%下降到 33%，这证实了 Pb 阳离子在吸附过程中被整合到真菌 EPS 中。对于存活的 R1 细胞，多糖抵抗 Pb 毒性的功能仅在 Pb(NO)水平极高（>=1500mg/L）时起作用。相比之下，蛋白质表现出持续增强的抵抗 Pb 毒性的能力，与它们在 EPS 中的含量（每细胞）增加一致。此外，ATR-IR 光谱显示 1540cm 处酰胺 II 峰的强度显著增加，表明 EPS 中的谷胱甘肽（GSH）增加。这表明 GSH 可能是 EPS 蛋白质中与 Pb 结合的关键成分。因此，本研究阐明了多糖和蛋白质在 EPS 中在重金属毒性作用下的作用。
