Key Laboratory of Groundwater Resources and Environment Ministry of Education, College of Environment and Resources, Jilin University, Changchun, 130012, China.
The First Hospital of Jilin University, Changchun, 130021, China.
Environ Pollut. 2019 Apr;247:1100-1109. doi: 10.1016/j.envpol.2019.01.005. Epub 2019 Jan 3.
The effects of fulvic acid (FA) and ions on mesophilic pathogenic bacteria survival under freeze-thaw (FT) stress in natural water and its resistant mechanisms are rarely understood. Therefore, survival patterns of Escherichia coli in river water added with various concentrations of FA or FA-ion under FT stress were studied in this work. Meanwhile, cell surface hydrophobicity (CSH), unit activities of superoxide dismutase (SOD) and catalase (CAT) were determined and Escherichia coli morphologies were observed to explore the bacterial resistant mechanisms against FT stress. The results demonstrated that FT cycles significantly reduced bacterial quantities as sampling time, i.e. freeze-thaw cycle time increased. And the biggest reducing rate was observed after the first FT cycle in every system. Ttd values, time needed to reach detection limit under FT stress decreased under FT stress as FA was added into water, while the changes of ttd values were quite complicated when FA and various ions existed together. Generally, the ttd values of FA-cation systems exceeded that of FA system except FA-Ca systems, but it was opposite for FA-anion systems. CSH was heightened after FT cycles and reached peak value at last sampling time in every system. Mechanical constraint from extracellular ice crystals and high CSH induced bacterial aggregation, which protect inner cells of aggregation from extracellular ice crystals. And the unit activities of SOD were significantly higher than those of CAT. Unit activities of SOD and CAT in large part of tested systems increased with sampling time under FT stress, which reduced reactive oxygen species produced from repeated FT cycles. Thus, these could improve the resistance of Escherichia coli to freeze-thaw stress and promote their survival. This work explored the survival pattern and strategy of Escherichia coli in natural water under FT stress.
富里酸（FA）及其离子对自然水中嗜温致病菌在冻融（FT）胁迫下的存活及其抗性机制的影响尚不清楚。因此，本研究考察了不同浓度 FA 或 FA-离子添加条件下河水水样中大肠杆菌在 FT 胁迫下的存活模式。同时，测定了细胞表面疏水性（CSH）、超氧化物歧化酶（SOD）和过氧化氢酶（CAT）的比活力，并观察了大肠杆菌的形态，以探讨其对 FT 胁迫的抗性机制。结果表明，FT 循环显著降低了细菌数量，随着采样时间（即冻融循环时间）的增加而减少。每个体系中，第一次 FT 循环后观察到最大的减少率。在 FT 胁迫下，添加 FA 会降低 Ttd 值（达到 FT 胁迫检测限所需的时间），而当 FA 与各种离子共存时，ttd 值的变化则相当复杂。一般来说，除 FA-Ca 体系外，FA-阳离子体系的 ttd 值均大于 FA 体系，但 FA-阴离子体系则相反。FT 循环后 CSH 升高，在每个体系的最后一次采样时达到峰值。细胞外冰晶的机械约束和高 CSH 导致细菌聚集，从而保护聚集物内的细胞免受细胞外冰晶的影响。并且 SOD 的单位活性明显高于 CAT。在 FT 胁迫下，大部分测试体系中的 SOD 和 CAT 单位活性随采样时间的增加而增加，从而减少了由反复 FT 循环产生的活性氧。因此，这可以提高大肠杆菌对冻融胁迫的抵抗力，促进其存活。本研究探讨了自然水中大肠杆菌在 FT 胁迫下的存活模式和策略。
