The high resilience of the bacterioplankton community in the face of a catastrophic disturbance by a heavy Microcystis bloom.

The accumulation and breakdown of cyanobacterial blooms often causes catastrophic changes in the aquatic fauna of lakes. Recovery from these changes is always prolonged. However, little is known about the resilience and recovery of the bacterioplankton community composition (BCC) after this type of disturbance. In this study, we examined the resistance and resilience of the BCC following a Microcystis bloom disturbance with in situ mesocosm experiments with varying levels of Microcystis biomass ranging from 75 to 13 012 μg L(-1) , as measured by the chlorophyll-a concentration, over 13 days. The BCC was assessed with denaturing gradient gel electrophoresis of 16S rRNA genes, followed by cloning and sequencing of the selected samples. We observed a strong shift of the BCC from the control on the first day of the bloom disturbance. The most dramatic change in the BCC occurred in the mesocosm with the highest Microcystis biomass, in which the dissolved oxygen varied strongly. However, we observed a rapid recovery of the BCC from day 7, when most of the investigated environmental factors had also recovered. On day 12, the BCC in the different mesocosms resembled the control at day 0 to a greater extent than during the accumulation and breakdown of the Microcystis bloom. Our study indicated that although the resistance of the BCC is low, the resilience is high, even following a catastrophic disturbance by a Microcystis bloom in a freshwater lake.