Inhibitory effect of malonic acid on Microcystis aeruginosa: Cell morphology, oxidative stress and gene expression

Abstract

The utilization of allelochemicals, which are regarded as eco-friendly algaecides for mitigating harmful cyanobacterial blooms (HCB), has attracted increasing attention, owing to their negligible toxicity, high selectivity and excellent degradability. In the present study, the inhibitory effects of malonic acid on Microcystis aeruginosa were investigated in terms of growth indicators, cell morphology, antioxidant enzymes activities and gene expression. The results indicated that the exposure to 0.5 mmol L−1 malonic acid for 7 d caused a high microalgae inhibition rate of 86.88 %. Furthermore, the analysis of scanning electron microscopy (SEM) and transmission electron microscope (TEM) showed that the presence of malonic acid resulted in the disruption of cell integrity and the changes in cell morphology. Specifically, malonic acid was observed to cleave microalgae cells, while concurrently oxidizing the microalgae organic matter. In addition, under the exposure of 0.5 mmol L−1 malonic acid, the levels of malondialdehyde (MDA) were 3.28 times as the control group on d-5, while the activities of superoxide dismutase (SOD) and catalase (CAT) were first increased by 5.96 and 11.73 fold compare to the control group on d-5, and then decreased, due to oxidative stress induced by malonic acid. Transcriptome-based gene expression analysis revealed that the presence of malonic acid significantly inhibited the transcription of genes (rbcL, psbA1) associated with photosynthesis, and the expression of DNA repair gene (recA), stress response gene (ftsH) and microcystin synthesis genes (mcyD, mcyH) were up-regulated. These findings provide novel insights into the inhibitory effect of malonic acid on M. aeruginosa, suggesting that malonic acid has the potential to control M. aeruginosa blooms.