Algae blooms with resistance in fresh water: Potential interplay between Microcystis and antibiotic resistance genes

Microcystis, a type of cyanobacteria known for producing microcystins (MCs), is experiencing a global increase in blooms. They have been recently recognized as potential contributors to the widespread of antibiotic resistance genes (ARGs). By reviewing approximately 150 pieces of recent studies, a hypothesis has been formulated suggesting that significant fluctuations in MCs concentrations and microbial community structure during Microcystis blooms could influence the dynamics of waterborne ARGs. Among all MCs, microcystin-LR (MC-LR) is the most widely distributed worldwide, notably abundant in reservoirs during summer. MCs inhibit protein phosphatases or increase reactive oxygen species (ROS), inducing oxidative stresses, enhancing membrane permeability, and causing DNA damage. This further enhances selective pressures and horizontal gene transfer (HGT) chances of ARGs. The mechanisms by which Microcystis regulates ARG dissemination have been systematically organized for the first time, focusing on the secretion of MCs and the alterations of bacterial community structure. However, several knowledge gaps remain, particularly concerning how MCs interfere with the electron transport chain and how Microcystis facilitates HGT of ARGs. Concurrently, the predominance of Microcystis forming the algal microbial aggregates is considered a hotspot for preserving and transferring ARGs. Yet, Microcystis can deplete the nutrients from other taxa within these aggregates, thereby reducing the density of ARG-carrying bacteria. Therefore, further studies are needed to explore the 'symbiotic - competitive' relationships between Microcystis and ARG-hosting bacteria under varied nutrient conditions. Addressing these knowledge gaps is crucial to understand the impacts of the algal aggregates on dynamics of waterborne antibiotic resistome, and underscores the need for effective control of Microcystis to curb the spread of antibiotic resistance. Constructed wetlands and photocatalysis represent advantageous strategies for halting the spread of ARGs from the perspective of Microcystis blooms, as they can effectively control Microcystis and MCs while maintaining the stability of aquatic ecosystem.