School of Civil and Environmental Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0512, USA.
School of Chemical and Biomolecular Engineering, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th Street, N.W., Atlanta, GA 30318, USA.
Water Res. 2014 Jul 1;58:71-81. doi: 10.1016/j.watres.2014.03.062. Epub 2014 Apr 2.
Phytosterols are plant-derived sterols present in pulp and paper wastewater and have been implicated in the endocrine disruption of aquatic species. Bioassays were performed to assess the effect of an additional carbon source and/or solubilizing agent on the aerobic biotransformation of a mixture of three common phytosterols (β-sitosterol, stigmasterol and campesterol). The aerobic biotransformation of the phytosterol mixture by a mixed culture developed from a pulp and paper wastewater treatment system was examined under three separate conditions: with phytosterols as the sole added carbon source, with phytosterols and dextrin as an additional carbon source, and with phytosterols added with ethanol as an additional carbon source and solubilizing agent. Significant phytosterol removal was not observed in assays set up with phytosterol powder, either with or without an additional carbon source. In contrast, all three phytosterols were aerobically degraded when added as a dissolved solution in ethanol. Thus, under the experimental conditions of this study, the bioavailability of phytosterols was limited without the presence of a solubilizing agent. The total phytosterol removal rate was linear for the first six days before re-spiking, with a rate of 0.47 mg/L-d (R(2) = 0.998). After the second spiking, the total phytosterol removal rate was linear for seven days, with a rate of 0.32 mg/L-d (R(2) = 0.968). Following the 7th day, the phytosterol removal rate markedly accelerated, suggesting two different mechanisms are involved in phytosterol biotransformation, more likely related to the production of enzyme(s) involved in phytosterol degradation, induced under different cell growth conditions. β-sitosterol was preferentially degraded, as compared to stigmasterol and campesterol, although all three phytosterols fell below detection limits by the 24th day of incubation.
植物甾醇是存在于纸浆和造纸废水中的植物衍生甾醇，已被牵连到水生物种的内分泌干扰中。进行生物测定以评估额外碳源和/或增溶剂对三种常见植物甾醇（β-谷甾醇、豆甾醇和菜油甾醇）混合物的好氧生物转化的影响。在三种不同条件下检查了从纸浆和造纸废水处理系统中开发的混合培养物对植物甾醇混合物的好氧生物转化：仅添加植物甾醇作为唯一外加碳源，添加植物甾醇和糊精作为外加碳源，以及添加植物甾醇和乙醇作为外加碳源和增溶剂。在添加植物甾醇粉末的测定中，无论是有无外加碳源，均未观察到明显的植物甾醇去除。相比之下，当以乙醇中的溶解溶液添加时，所有三种植物甾醇均被好氧降解。因此，在本研究的实验条件下，在不存在增溶剂的情况下，植物甾醇的生物利用度受到限制。在前六天重新添加之前，总植物甾醇去除率呈线性，去除率为 0.47 mg/L-d（R(2) = 0.998）。第二次添加后，总植物甾醇去除率在七天内呈线性，去除率为 0.32 mg/L-d（R(2) = 0.968）。第 7 天后，植物甾醇去除率明显加快，这表明植物甾醇生物转化涉及两种不同的机制，更可能与参与植物甾醇降解的酶的产生有关，这是在不同的细胞生长条件下诱导的。与豆甾醇和菜油甾醇相比，β-谷甾醇优先降解，尽管所有三种植物甾醇在孵育的第 24 天都低于检测限。
