Modifying luteolin's algicidal effect on Microcystis by virgin and diversely-aged polystyrene microplastics: Unveiling novel mechanisms through microalgal adaptive strategies

Abstract

Luteolin has shown great potential in inhibiting Microcystis-dominated cyanobacterial blooms (MCBs). However, widespread microplastics (MPs) in natural aquatic systems can serve as substrates for cyanobacterial growth, potentially impacting their resistance to external stress and might interfere with luteolin's algicidal effect. This study investigated the impact of virgin and diversely-aged polystyrene microplastics (PS-MPs) on the inhibitory effect of luteolin involving Microcystis growth and microcystins (MCs) content in water. Moreover, the underlying mechanism was also revealed by jointly analyzing the SEM images, oxidative stress, exopolymeric substances (EPSs) content and functional gene expression. Result suggested that 0.5, 5 and 50 mg/L virgin and diversely-aged PS-MPs almost reduced growth inhibition ratio and oxidative damage of Microcysits by both doses of luteolin by stimulating EPSs secretion and inducing cell self-aggregate or hetero-aggregate with PS-MPs. Compared to virgin PS-MPs, photo-aged PS-MPs possessed rougher flaky surfaces, and hydrothermal-aging cracks the MPs internally, which were more conducive to interacting and hetero-aggregating with cells, and exhibiting more significant protective effects to Microcystis. However, MPs further reduced MCs content in water, possibly attributed to their adsorption effect on MCs, compared to luteolin stress alone. Such toxic hetero-aggregate formed by MCs, MPs, and Microcystis cells are more likely to be consumed, thus entering the food chain and triggering toxic bioaccumulation, posing greater eco-risks. This is the first study to clarify the impact and mechanisms of virgin and diversely-aged MPs on allelopathic algicidal effects from the perspective of microalgal inherent detoxifying abilities and self-protective strategies.