Effects of rhamnolipids on growth， microcystin production and release of <italic>Microcystis aeruginosa</italic>

Rhamnolipid， a common biosurfactant， has an inhibitory effect on some marine microalgae. To investigate the effects of rhamnolipids on the growth and microcystin production of Microcystis aeruginosa and the impact mechanism， the growth， microcystin production and release， intracellular oxygen radicals， malondialdehyde content， and cell membrane morphology of Microcystis aeruginosa under rhamnolipid stress were measured. The results indicated that 8 mg/L rhamnolipid inhibited more than 90% of Microcystis aeruginosa at the beginning of the logarithmic growth period by day 10， and 95.5% by the end of the test， with significant inhibition of algal growth within 21 days. Rhamnolipids enhanced the MC-LR production capacity of the algal cells， with the mcyD gene up-regulated to 1.1 times that of the blank group， but the total amount of MC-LR produced by the algal cells was significantly reduced， and no significant difference in the amount of extracellular MC-LR released was observed. The overloading of superoxide anion in algal cells under rhamnolipid stress caused lipid peroxidation of cell membranes， decomposition of membrane lipids into malondialdehyde， disruption of membrane structure， and consequent release of intracellular MC-LR. The result can provide a theoretical basis for the practical application of rhamnolipids.鼠李糖脂（rhamnolipid）是一种常见的生物表面活性剂，对部分海洋微藻具有抑制作用。为探究鼠李糖脂对铜绿微囊藻（Microcystis aeruginosa）生长及产毒特性的影响及其作用机制，本研究测定了铜绿微囊藻在鼠李糖脂胁迫下的生长情况、微囊藻毒素的产生与释放、细胞内氧自由基水平、丙二醛含量以及细胞膜形态。结果表明，8 mg/L的鼠李糖脂在对数生长期初期（第10天）即可抑制90%以上的铜绿微囊藻，试验结束时抑制率可达95.5%，且在21天内对藻类生长具有显著抑制效果。鼠李糖脂可提升藻细胞的微囊藻毒素-LR（MC-LR）合成能力，其mcyD基因的表达量上调至空白组的1.1倍，但藻细胞总MC-LR产量显著降低，且胞外释放的MC-LR总量无显著差异。鼠李糖脂胁迫下，藻细胞内超氧阴离子过载会引发细胞膜脂质过氧化，膜脂降解为丙二醛，破坏膜结构并最终导致胞内MC-LR释放。本研究结果可为鼠李糖脂的实际应用提供理论依据。