Interspecific interactions modulate atrazine and S-metolachlor toxicity on aquatic microbial autotrophs

Atrazine and S-metolachlor are frequently detected herbicides in streams in agricultural areas, sometimes at concentrations of concern that may affect photosynthetic organisms. In the present study, we exposed a coculture of the green alga Enallax costatus, the diatom Gomphonema parvulum and the cyanobacteria Phormidium sp. and Microcystis aeruginosa to a gradient of atrazine and S-metolachlor (0, 10, 100 and 1000 µg·L-1) for 7 days. The results showed that species interactions in a coculture can modulate herbicide toxicity compared to responses observed in monocultures. Green algae and cyanobacteria were more sensitive to atrazine in coculture than in monoculture, while diatoms showed better tolerance in coculture. S-metolachlor affected the chlorophyll fluorescence of organisms in coculture to a greater extent than atrazine, particularly for the green alga and the diatom. Despite its mode of action as an inhibitor of the synthesis of very long chain fatty acids (VLCFAs), S-metolachlor did not result in a significant reduction in these fatty acids. In general, the two herbicides had a more pronounced effect on fluorescence than on lipids in coculture. The modification in photosynthetic organisms composing the coculture was accompanied by a change in fatty acid profiles, reflecting the specific fatty acid profiles of each group of organisms. In addition, herbicide exposure may have caused lipid peroxidation, leading to a decrease in the relative abundance of polyunsaturated fatty acids (PUFAs) in the coculture. This study highlights the importance of considering interspecific interactions in ecotoxicology, as they can modulate herbicide toxicity on aquatic photosynthetic communities. In addition, lipid and fatty acid profiles provide sensitive information that complements ‘traditional’ descriptors such as cell density and photosynthesis parameters. Lipidomics can be used to study changes in coculture composition (community composition) as well as to assess the potential of herbicides to affect organisms at the cellular level.

莠去津（Atrazine）与异丙甲草胺（S-metolachlor）是农业区域溪流中频繁检出的除草剂，部分检出浓度已达到值得关注的水平，可能对光合生物造成不良影响。本研究将由被衣藻（Enallax costatus）、小型异极藻（Gomphonema parvulum）、席藻属（Phormidium sp.）及铜绿微囊藻（Microcystis aeruginosa）组成的共培养体系，置于含有不同浓度梯度莠去津与异丙甲草胺（0、10、100及1000 µg·L⁻¹）的培养基中培养7天。研究结果显示，相较于单培养体系中的生物响应，共培养体系内的物种相互作用可调控除草剂的毒性效应。共培养体系中，绿藻与蓝细菌对莠去津的敏感性显著高于单培养体系，而硅藻则在共培养环境中表现出更强的耐受性。异丙甲草胺对共培养体系中生物的叶绿素荧光的影响程度强于莠去津，尤其对绿藻与硅藻的影响更为显著。尽管其作用机制为超长链脂肪酸（very long chain fatty acids, VLCFAs）合成抑制剂，但异丙甲草胺并未引发此类脂肪酸的显著减少。总体而言，在共培养体系中，两种除草剂对叶绿素荧光的影响显著强于对脂质的影响。共培养体系内光合生物的组成变化伴随脂肪酸谱的改变，这一现象反映了不同类群生物特有的脂肪酸谱特征。此外，除草剂暴露可能引发脂质过氧化反应，导致共培养体系中多不饱和脂肪酸（polyunsaturated fatty acids, PUFAs）的相对丰度降低。本研究强调了在生态毒理学研究中考虑种间相互作用的重要性，因为此类相互作用可调控除草剂对水生光合群落的毒性效应。此外，脂质与脂肪酸谱可提供敏感的检测信息，作为细胞密度、光合参数等“传统”表征指标的有效补充。脂质组学（lipidomics）可用于探究共培养体系的群落组成变化，同时也可用于评估除草剂在细胞层面影响生物的潜在风险。