Rudjer Boskovic Institute, Division for Marine and Environmental Research, HR-10002, Zagreb, Croatia.
University of Thessaly, Department of Biochemistry and Biotechnology, Ploutonos 26 and Aeolou Str, 412 21, Larisa, Greece.
Environ Sci Pollut Res Int. 2016 Mar;23(5):4320-33. doi: 10.1007/s11356-015-5645-6. Epub 2015 Oct 31.
The action mode of sulfonylurea herbicides is the inhibition of the acetohydroxyacid synthase (AHAS) required for the biosynthesis of amino acids valine and isoleucine in plants. However, this enzyme is also present in a range of non-targeted organisms, among which soil microorganisms are known for their pivotal role in ecosystem functioning. In order to assess microbial toxicity of sulfonylurea herbicide nicosulfuron (NS), a tiered microcosm (Tier I) to field (Tier II) experiment was designed. Soil bacteria harboring AHAS enzyme tolerant to the herbicide nicosulfuron were enumerated, isolated, taxonomically identified, and physiologically characterized. Results suggested that application of nicosulfuron drives the selection towards NS-tolerant bacteria, with increasing levels of exposure inducing an increase in their abundance and diversity in soil. Tolerance to nicosulfuron was shown to be widespread among the microbial community with various bacteria belonging to Firmicutes (Bacillus) and Actinobacteria (Arthrobacter) phyla representing most abundant and diverse clusters. While Arthrobacter bacterial population dominated community evolved under lower (Tier II) nicosulfuron selection pressure, it turns out that Bacillus dominated community evolved under higher (Tier I) nicosulfuron selection pressure. Different NS-tolerant bacteria likewise showed different levels of sensitivity to the nicosulfuron estimated by growth kinetics on nicosulfuron. As evident, Tier I exposure allowed selection of populations able to better cope with nicosulfuron. One could propose that sulfonylureas-tolerant bacterial community could constitute a useful bioindicator of exposure to these herbicides for assessing their ecotoxicity towards soil microorganisms.
磺酰脲类除草剂的作用模式是抑制植物中必需氨基酸缬氨酸和异亮氨酸生物合成所需的乙酰羟酸合酶 (AHAS)。然而，这种酶也存在于一系列非靶标生物中，其中土壤微生物以其在生态系统功能中的关键作用而闻名。为了评估磺酰脲类除草剂烟嘧磺隆 (NS) 对微生物的毒性，设计了一个从微宇宙 (第 I 层)到野外 (第 II 层)的分层实验。对含有对除草剂烟嘧磺隆具有耐受性的 AHAS 酶的土壤细菌进行了计数、分离、分类鉴定和生理特征分析。结果表明，烟嘧磺隆的使用会导致对 NS 耐受细菌的选择，随着暴露水平的增加，土壤中它们的丰度和多样性也会增加。研究表明，对烟嘧磺隆的耐受性在微生物群落中广泛存在，各种属于厚壁菌门（芽孢杆菌）和放线菌门（节杆菌）的细菌代表了最丰富和最多样化的聚类。虽然在较低（第 II 层）烟嘧磺隆选择压力下，节杆菌种群主导的群落进化，但事实证明，在较高（第 I 层）烟嘧磺隆选择压力下，芽孢杆菌主导的群落进化。不同的 NS 耐受细菌对烟嘧磺隆的敏感性也不同，这可以通过在烟嘧磺隆上的生长动力学来估计。显然，第 I 层暴露允许选择能够更好地应对烟嘧磺隆的种群。人们可以提出，对磺酰脲类耐受的细菌群落可以作为这些除草剂暴露的有用生物标志物，用于评估它们对土壤微生物的生态毒性。
