Growth and reproduction vary between individual cells and particle aggregates of cyanobacteria

Cyanobacteria grown in the laboratory or cultivated commercially present a uniformly dispersed state of cells without particle aggregation. This growth pattern differs significantly from the suspended particle-like growth characteristic of cyanobacterial populations in natural blooms. Such particles are highly likely to engage in cooperation, environmental adaptation, and metabolic regulation by aggregating. This study aimed to systematically compare the growth characteristics and metabolic responses of individual cyanobacterial cells and particles to identify the key role of population morphology in environmental adaptation and in the formation and maintenance of blooms.

This study used a laboratory-scale, controlled culture system to treat individual cells or particles with different nutritional stresses. The responses were systematically evaluated by monitoring key physiological indicators, including morphological characteristics, dynamic changes in chlorophyll a content, photochemical efficiency (Fv/Fm), and metabolic release characteristics.

The results showed that individual cells were mainly 3–7 μm in diameter, while the particles were primarily between 200–650 μm. Compared with individual cells, the particles exhibited stronger stress tolerance. Under nutritional adversity, biomass decrease was much lower in particles than in individual cells (47.82% vs. 85.22% decline in chlorophyll a), while maintaining photochemical efficiency at a higher level. Population structure effectively delayed cell death. Second, metabolic response patterns differed markedly between the two types. When environmental nutritional composition changed, cyanobacterial particles switched metabolic mechanisms by increasing the production and secretion of humic- and fulvic-like compounds to adopt survival strategies. Under nutritional limitation, although the release of organic compounds by cyanobacterial particles and individual cells was enhanced, organic matter increased relatively meagerly in particles. In contrast, individual cells were more prone to loss of structural integrity under adversity, leading to leakage of intracellular components, which had a significantly greater proportion of protein-like material than organic compounds. From a physiological and metabolic correlation perspective, these results suggest that population morphology involves the construction of a localized microenvironment that effectively buffers the direct impacts of external stress.

Cyanobacteria can significantly enhance their environmental stress buffering capacity and metabolic plasticity by forming particle aggregates. Such a mechanism is key for maintaining physiological function and improving resistance under adverse conditions, such as nutritional stress. It enables cyanobacterial populations to demonstrate a significant advantage in inter- and intraspecific competition in natural water bodies, providing a crucial theoretical and experimental basis for the formation and long-term maintenance of cyanobacterial blooms.