Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
Water Res. 2012 Oct 15;46(16):5028-36. doi: 10.1016/j.watres.2012.06.040. Epub 2012 Jul 6.
The role that antibiotics and other "emerging contaminants" play in shaping environmental microbial communities is of growing interest. The use of the prokaryotic metabolic inhibitors tylosin (T), lincomycin (L), and ciprofloxacin (C) in livestock and humans is both global and extensive. Each of these antibiotic compounds exhibits an affinity for sediment particles, increasing the likelihood of their deposition in the benthos of aquatic systems and each are often present in environmental samples. The purpose of this study was to determine if T, L, and C and their mixtures exhibit significant toxicity to two species of marine diatoms, an algal class comprised of ubiquitous eukaryotic primary producers. Subpopulations from laboratory cultures of Cylindrotheca closterium and Navicula ramosissima were reared in 24-well microtiter plates in the presence of single or combined antibiotics in dilution series. Population growth rates were assessed via epifluorescent microscopic cell counts, from which the half-max inhibitory concentrations (IC(50)) were calculated and used as part of a toxic unit (TU) method for assessing mixture interactions. The single-compound IC(50)'s were, for C. closterium: T = 0.27 mg L(-1), L = 14.16 mg L(-1), C = 55.43 mg L(-1), and for N. ramosissima: T = 0.99 mg L(-1), L = 11.08 mg L(-1), C = 72.12 mg L(-1). These values were generally higher than similar metrics for freshwater species. Mixture IC(50)'s were generally synergistic against C. closterium and additive for N. ramosissima. Both single and combined treatments reduced or eliminated diatom motility. Monochemical responses were similar between species and were not useful for predicting mixture interactions. Mixtures had compound-specific and species-specific effects, favoring N. ramosissima. These results suggest that anthropogenic antibiotics may play a significant role in the ecology of environmental benthic microbial communities. They also suggest single-compound/species studies do not yield useful predictions of the ecological impact of anthropogenic pharmaceuticals.
抗生素和其他“新兴污染物”在塑造环境微生物群落方面的作用越来越受到关注。在全球范围内，广泛使用抗生素泰乐菌素（T）、林可霉素（L）和环丙沙星（C）来治疗牲畜和人类疾病。这些抗生素化合物都对沉积物颗粒具有亲和力，增加了它们在水生系统底栖环境中沉积的可能性，并且它们经常存在于环境样本中。本研究的目的是确定 T、L 和 C 及其混合物对两种海洋硅藻（一种普遍存在的真核初级生产者）是否具有显著毒性。从实验室培养的 Cylindrotheca closterium 和 Navicula ramosissima 的亚种群在 24 孔微量滴定板中培养，在稀释系列中存在单一或组合抗生素。通过荧光显微镜细胞计数评估种群增长率，从中计算出半最大抑制浓度（IC 50 ），并用作评估混合物相互作用的毒性单位（TU）方法的一部分。单一化合物的 IC 50 值为：C. closterium：T = 0.27 mg L(-1)，L = 14.16 mg L(-1)，C = 55.43 mg L(-1)，N. ramosissima：T = 0.99 mg L(-1)，L = 11.08 mg L(-1)，C = 72.12 mg L(-1)。这些值通常高于类似的淡水物种的度量值。混合物 IC 50 值通常对 C. closterium 具有协同作用，对 N. ramosissima 具有加性作用。单一和组合处理均降低或消除了硅藻的运动性。单一化合物的反应在物种之间相似，并且不能用于预测混合物相互作用。混合物具有化合物特异性和物种特异性的影响，有利于 N. ramosissima。这些结果表明，人为抗生素可能在环境底栖微生物群落的生态学中发挥重要作用。它们还表明，单一化合物/物种研究不能对人为药物的生态影响做出有用的预测。
