School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan, 430072, China.
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan, 430072, China; The James Hutton Institute, Craigiebuckler, Aberdeen, ABI5 8QH, UK.
Chemosphere. 2022 Mar;291(Pt 2):132878. doi: 10.1016/j.chemosphere.2021.132878. Epub 2021 Nov 12.
As an important carbon (C) storage in biological soil crusts (BSCs), exopolysaccharides (EPSs) are not only a part of the desert C cycle, but also the key materials for cyanobacteria to resist desert stress. In this study, the influence of initial N concentrations (10, 25 and 50 mg L designated as N10, N25 and N50 respectively) on Microcoleus vaginatusis growth and the excretion of EPSs including RPS (released exopolysaccharides) and CPS (capsule exopolysaccharides) were evaluated at different growth periods. In logarithmic period, higher ratio of biomass to EPSs indicated by (DW-CPS)/EPSs was observed in the N50 group with the highest N concentration (about 40 mg L) in the medium, while no difference was observed among the three groups in stationary period when the N concentrations of medium were lower than 25 mg L. The CPS/RPS showed similar results with (DW-CPS)/EPSs, and stayed higher than 1 in each group. Notably, obvious difference displayed in the monosaccharidic composition and morphologies between CPS and RPS, but not the N levels. The changes of C/N in cells at different growth period indicate that the excretion of EPSs, a mechanism that maintains the balance of cell C/N ratio, only works when the N in the environment is sufficient. Our results showed that, as the raw material and environmental signal, environmental N concentration regulates the elements (C and N) percentage of cyanobacterial cells and its EPSs excretion pattern, but not the monosaccharidic composition or the morphologies. These results also implied that, as the essential self-protecting materials, more EPSs with higher proportion of CPS would be excreted to response the low N environment.
作为生物土壤结皮（BSC）中重要的碳（C）储存库，胞外多糖（EPS）不仅是沙漠碳循环的一部分，也是蓝细菌抵抗沙漠胁迫的关键物质。本研究评估了不同初始氮浓度（10、25 和 50mgL 分别表示为 N10、N25 和 N50）对微鞘藻生长和 EPS（包括 RPS（释放的胞外多糖）和 CPS（胶囊胞外多糖））排泄的影响。在对数生长期，在培养基中具有最高氮浓度（约 40mgL）的 N50 组中观察到更高的生物量与 EPS 之比（DW-CPS）/EPSs，而在氮浓度低于 25mgL 的静止期，三组之间没有差异。CPS/RPS 表现出与（DW-CPS）/EPSs 相似的结果，并且在每组中均高于 1。值得注意的是，CPS 和 RPS 之间在单糖组成和形态上存在明显差异，但在氮水平上没有差异。不同生长时期细胞中 C/N 的变化表明，EPS 的排泄（一种维持细胞 C/N 比平衡的机制）仅在环境中的 N 充足时起作用。我们的结果表明，作为原料和环境信号，环境氮浓度调节蓝细菌细胞的元素（C 和 N）百分比及其 EPS 排泄模式，但不调节单糖组成或形态。这些结果还暗示，作为必需的自我保护材料，将分泌更多比例更高的 CPS 的 EPS 以响应低 N 环境。
