Rapid flotation of Microcystis wesenbergii mediated by high light exposure: implications for surface scum formation and cyanobacterial species succession

Front Plant Sci. 2024 Apr 3:15:1367680. doi: 10.3389/fpls.2024.1367680. eCollection 2024.


Increasing occurrences of Microcystis surface scum have been observed in the context of global climate change and the increase in anthropogenic pollution, causing deteriorating water quality in aquatic ecosystems. Previous studies on scum formation mainly focus on the buoyancy-driven floating process of larger Microcystis colonies, neglecting other potential mechanisms. To study the non-buoyancy-driven rapid flotation of Microcystis, we here investigate the floating processes of two strains of single-cell species (Microcystis aeruginosa and Microcystis wesenbergii), which are typically buoyant, under light conditions (150 μmol photons s-1 m-2). Our results showed that M. wesenbergii exhibited fast upward migration and formed surface scum within 4 hours, while M. aeruginosa did not form visible scum throughout the experiments. To further explore the underlying mechanism of these processes, we compared the dissolved oxygen (DO), extracellular polymeric substance (EPS) content, and colony size of Microcystis in different treatments. We found supersaturated DO and the formation of micro-bubbles (50-200 µm in diameter) in M. wesenbergii treatments. M. aeruginosa produces bubbles in small quantities and small sizes. Additionally, M. wesenbergii produced more EPS and tended to aggregate into larger colonies. M. wesenbergii had much more derived-soluble extracellular proteins and polysaccharides compared to M. aeruginosa. At the same time, M. wesenbergii contains abundant functional groups, which was beneficial to the formation of agglomerates. The surface scum observed in M. wesenbergii is likely due to micro-bubbles attaching to the surface of cell aggregates or becoming trapped within the colony. Our study reveals a species-specific mechanism for the rapid floatation of Microcystis, providing novel insights into surface scum formation as well as succession of cyanobacterial species.

Keywords: Microcystis; cell aggregation; extracellular polymeric substance; micro-bubbles; surface scum formation.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study was financially supported by China’s National Key R&D Programmes (2022YFC3203601), Hubei Province Postdoctoral Innovation Research Position (Letter No. 153 of Hubei Human Resources and Social Security). Additional support was provided by the National Natural Science Foundation of China (42061134013) and the Yunnan Province-Kunming City Major Science and Technology Project (202202AH210006). Additionally, the authors are indebted to Yuan Xiao, and Fang Zhou (Analysis and Testing Center, Institute of Hydrobiology, CAS), and the Laboratory for Downstream Process Technology and Engineering of Microalgae (LDPTEM) for lab equipment support.