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Molecular Probe Optimization to Determine Cell Mortality in a Photosynthetic Organism Microcystis aeruginosa Using Flow Cytometry
Published on: January 29, 2016
Comprehensive comparisons on the apoptosis of cyanobacteria, green algae, and diatoms under metalimnetic oxygen
Ruihua Cao1, Xi-Jun Wu2, Na Zhang1
1Key Laboratory of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
Abstract:
Algal blooms (including cyanobacteria, green algae, and diatoms) suspended in the metalimnion can lead to the formation of metalimnetic oxygen minimum (MOM). Understanding the fate of the three algal bloom species under MOM conditions helps assess water quality risks. In this study, the apoptosis process of Microcystis aeruginosa (M. aeruginosa), Chlorella vulgaris (C. vulgaris), and Cyclotella meneghiniana (C. meneghiniana), as well as the subsequent algal organic matter (AOM) release, was investigated and compared. MOM stress induced a sequential physiological failure across all species. The decline in viability occurred in the following sequence: first in photosynthetic activity, followed by membrane integrity, and finally in algal density. Notably, C. meneghiniana exhibited the highest membrane damage rate (2.47 min-1), significantly surpassing that of M. aeruginosa (0.66 min-1) and C. vulgaris (0.44 min-1), indicating its superior susceptibility. It can be attributed to a critical energy imbalance: the larger size and higher single-cell photosynthetic activity (1.92/106 cells) resulted in excessive metabolic energy demands under MOM conditions (darkness), accelerating algal apoptosis. Consistent with its rapid membrane damage, C. meneghiniana triggered a swift AOM release within just 4 days, whereas M. aeruginosa and C. vulgaris showed a delayed response after 20 days. Crucially, the AOM released from C. meneghiniana was not only more abundant (0.8-1.75 mg/L vs. 0.08-0.16 mg/L) but also of greater concern, featuring higher aromaticity, fluorescence intensity, and disinfection byproduct formation potential at the same algae density. It revealed that species-specific apoptosis pathways under MOM conditions are a key determinant of AOM quantity and quality. Therefore, understanding the persistence of algae and AOM release under MOM conditions facilitates the monitoring and management strategies of water quality in a stratified reservoir.
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