Structural Variations Increase the Upper Limit of Colony Size ofMicrocystis: Implications from Laboratory Cultures and Field Investigations

WildMicrocystishave highly diverse colonial structures and sizes, including variable colony geometry, cell arrangement, and diameter. These structural and dimensional variations may play an important role in continual, frequentMicrocystisblooms during summer and autumn, the cause of which still remains unclear. Here, laboratory cultures and field investigations were applied to assess mechanisms that drive variation in structure and size, as well as factors that influence diversity. The results demonstrated that colonies grew to large sizes at the expense of their structure being loose and inhomogeneous. Furthermore, colonies may spontaneously change structure to relieve the constraints of size in return. Influencing factors (nutrient limits and turbulent shear) tended to promote these variations. Our work highlights that the diversity ofMicrocystiscolonies may be a result of structural variations as survival strategies for gaining a higher upper size limit. Therefore, during seasonal successions, large colonies commonly have porous or loosely arranged structures, such as inM. aeruginosa. Additionally, this study hypothesized three possible transition routes for better understanding structural diversity and variations inMicrocystis.