Differences in survivability and toxic potential among Microcystis colonies of different sizes in sediment.

Microcystis colonies have the ability to persist for extended periods in sediment and function as a "seed bank" for the succeeding summer bloom in water column. The colonial morphology and toxin production ability of Microcystis are important for their population maintenance and life history. However, it is unclear about the influence of the colony morphology and toxic potential of Microcystis colonies on their benthic process. To address this question, we classified field Microcystis samples into three groups based on their size (< 150 μm, 150-300 μm, and > 300 μm) and compared their survivability and toxic potential during culturing in sediment. The results showed that Microcystis colonies in sediments disappeared quickly at 25℃ but survived for long periods at 5℃. The survivability of smaller Microcystis colonies (< 300 μm) was significantly higher than that of larger ones (> 300 μm). The activities of catalase (CAT) were significantly increased in large colonies compared to small colonies at 15℃ and 25℃. Real-time PCR indicated that smaller colonies had higher proportion of potential toxic genotype, and Microcystis colonies cultured at 15℃ and 25℃ showed higher percentage of microcystin-producing genotype. These results indicate that Microcystis colonies survived longer at low temperature and that larger Microcystis colonies are more susceptible to oxidative stress in sediments. The difference of toxic potential of Microcystis colonies of different sizes in sediments may be related to their survival ability in sediments.