PDF(Pubmed)
Abstract：
Surface blooms of colony-forming Microcystis are increasingly occurring in aquatic ecosystems on a global scale. Recent studies have found that the Microcystis colonial morphology is a crucial factor in the occurrence, persistence, and dominance of Microcystis blooms, yet the mechanism driving its morphological dynamics has remained unknown. This study conducted a laboratory experiment to test the effect of extracellular polymeric substances on the morphological dynamics of Microcystis. Ultrasound was used to disaggregate colonies, isolating the cells and of the Microcystis suspension. The single cells were then re-cultured under three homologous EPS concentrations: group CK, group Low, and group High. The size, morphology, and EPS [including tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS), bound polysaccharides (B-polysaccharides), and bound proteins (B-proteins)] changes of colonies were closely monitored over a period of 2 months. It was observed that colonies were rapidly formed in group CK, with median colony size (D50) reaching 183 µm on day 12. The proportion of colonies with a size of 150-500 µm increased from 1% to more than 50%. Colony formation was also observed in both groups Low and High, but their D50 increased at a slower rate and remained around 130 µm after day 17. Colonies with a size of 50-150 µm account for more than 50%. Groups CK and Low successively recovered the initial Microcystis morphology, which is a ring structure formed of several small colonies with a D50 of 130 µm. During the recovery of the colony morphology, the EPS per cell increased and then decreased, with TB-EPS and B-polysaccharides constituting the primary components. The results suggest that colony formation transitioned from adhesion driven to being division driven over time. It is suggested that the homologous EPS released into the ambient environment due to the disaggregation of the colony is a chemical cue that can affect the formation of a colony. This plays an important but largely ignored role in the dynamics of Microcystis and surface blooms.
摘要：
在全球范围内，水生生态系统中越来越多地出现形成菌落的微囊藻的表面水华。近年来研究发现微囊藻的集落形态是其发生的关键因素,持久性,和微囊藻的优势，然而，驱动其形态动力学的机制仍然未知。本研究进行了一项实验室实验，以测试胞外聚合物对微囊藻形态动力学的影响。超声波用于分解菌落，分离细胞和微囊藻悬液。然后在三个同源EPS浓度下重新培养单细胞：CK组，组低,组高。大小,形态学,和每股收益[包括紧密绑定的每股收益(TB-EPS)，松绑每股收益(LB-每股收益)，结合多糖（B-多糖），和结合蛋白（B蛋白）]在2个月的时间内密切监测菌落的变化。观察到在CK组中迅速形成菌落，在第12天，菌落大小中位数（D50）达到183µm。大小为150-500µm的菌落的比例从1％增加到50％以上。在低和高两组中也观察到集落形成，但他们的D50以较慢的速度增加，并在第17天后保持在130µm左右。大小为50-150μm的菌落占50％以上。CK组和Low组相继恢复了微囊藻的初始形态，它是由几个小菌落形成的环状结构，D50为130µm。在菌落形态恢复过程中，每个细胞的EPS先增加后减少，其中TB-EPS和B-多糖构成主要成分。结果表明，随着时间的推移，集落形成从粘附驱动转变为分裂驱动。建议由于菌落的解聚而释放到周围环境中的同源EPS是可能影响菌落形成的化学线索。这在微囊藻和表面水华的动力学中起着重要但在很大程度上被忽略的作用。
