Potential Risk and Mechanism of Microcystin Induction by Chiral Metalaxyl

Abstract

Pesticide-induced oxidative stress has been widely observed in aquatic algae. The production of microcystin caused by Microcystis aeruginosa intensified under the oxidative stress induced by solar radiation during an algal bloom. However, whether oxidative stress caused by the pollutants also contributed to toxic microcystin generation and the potential mechanism remain unknown, especially for chiral environmental contaminants. Metalaxyl, a high-volume chiral fungicide, was selected as the model to compare the risks to M. aeruginosa. Our results revealed a significant induction of algal growth or photosynthetic pigments at 30−50 mg/L R-metalaxyl (fungicidally active enantiomer) compared with 300−400 mg/L racmetalaxyl at 48 h. At the nontoxic time point, the lowest observed effect concentration (LOEC) of reactive oxygen species (ROS) induction was 10 mg/L in R-metalaxyl, which was 30 times lower than the corresponding value for the rac form. The LOECs of extra-and intra-microcystin induction of R-metalaxyl were 3.3 and 30.0 times higher than that of rac-metalaxyl, respectively. R-Metalaxyl enantioselectively induced M. aeruginosa genes encoding components of microcystin synthesis and secretion. The potency estimation revealed that only the level of ROS and genes encoding microcystin synthesis were positively correlated with the upregulation of intra-microcystin. Furthermore, we confirmed that attenuation of ROS by N-acetylcysteine mostly alleviated intra-microcystin induction. This demonstrates that the enantiomer that can cause oxidative stress may pose risks to the aquatic system, especially during an algal bloom.

Differential responses of two cyanobacterial species to R-metalaxyl toxicity: Growth, photosynthesis and antioxidant analyses

“…Our results revealed that R-metalaxyl treatment induced significant oxidative damage in both A. laxa and N. muscorum. In agreement, Wang et al (2018) reported that R-metalaxyl enantioselectively induced oxidative stress in the cyanobacterium M. aeruginosa. Metalaxyl stress induced a cell damage e.g., lipid peroxidation and DNA damage that was mainly mediated through ROS generation (de Sousa et al, 2013(de Sousa et al, , 2017.…”

“…Metalaxyl toxicity inhibited mitotic cell division by impairing the biosynthesis of RNA (Fisher and Hayes, 1982). It also inhibited the nitrogen fixation (Monkiedje et al, 2002) and the photosynthetic reactions (de Sousa et al, 2017) and induced oxidative stress in M. aeruginosa (Wang et al, 2018). On the other hand, higher plants could mitigate metalaxyl induced-oxidative damage by increasing their cellular antioxidant defenses (Teixeira et al, 2011;de Sousa et al, 2013de Sousa et al, , 2017.…”

Synthesis, biological evaluation, and molecular docking of novel ferulic acid derivatives containing a 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine skeleton

“…1 While pesticides remain a crucial component in the arsenal against these diseases in modern farming practices, their indiscriminate and prolonged use has given rise to two signicant challenges. [2][3][4] Firstly, it has led to the rapid development of resistance among pathogens, rendering many pesticides less effective. Secondly, the environmental pollution caused by these chemicals has become a cause for serious concern.…”

Exploiting Natural Maltol for Synthesis of Novel Hydroxypyridone Derivatives as Promising Anti-Virulence Agents in Bactericides Discovery

“…After invading rice plants, Xoo multiplies rapidly and disperses to the xylem vessels, causing symptoms of blight disease on rice leaves . These susceptible crops generally show up to 80% reduction in yield in severe cases. , Although chemical control has substantially contributed in alleviating diseases caused by plant pathogens, the long-term use of traditional agrochemicals (bismerthiazol [BT] and thiodiazole copper [TC]) has led to the predicament of resistance and aggravated environmental pollution because of the increasing dosages required for ensuring control efficiency. , For example, bismerthiazol has been observed to have less inhibitory activity than before against Xoo due to the emergence of BT-resistant strains. − These problems highlight the need to identify green pesticides bearing broad-spectrum antibacterial activity and novel action mechanisms to manage these plant bacterial diseases.…”