Haghighi Omid, Shahryari Shahab, Ebadi Mojgan, Modiri Sima, Zahiri Hossein Shahbani, Maleki Hadi, Noghabi Kambiz Akbari
Division of Industrial & Environmental Biotechnology, National Institute of Genetic Engineering and Biotechnology (NIGEB), P.O. Box 14155-6343, Tehran, Iran.
Department of Microbiology and Microbial Biotechnology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran.
Environ Toxicol Pharmacol. 2017 Apr;51:142-155. doi: 10.1016/j.etap.2017.03.008. Epub 2017 Mar 18.
In this study, we isolated five indigenous cyanobacterial strains from different aqueous environments, with heavy metals contamination, in East Azerbaijan Province (northwest portion of Iran). A strain was identified by morphological and 16S rRNA sequence analysis as Limnothrix sp. KO05 and selected for further studies as having the greatest potential for cadmium uptake. Scanning electron microscopy (SEM) demonstrated cyanobacterium Limnothrix sp. KO05 forms filamentous structures and is straight or curved to some extent. The utmost biosorption capacity was found to be 82.18±1.22mgg at a Cd (II) concentration level of 150mgL. Langmuir adsorption isotherm indicated a better fit to the experimental data. Response surface methodology (RSM) on the basis of four independent variables and the predicted maximum biosorption efficiency was 98.7% under the optimum condition. FT-IR spectroscopy profile of the Cd treated sample as demonstrated in confirmation of the benefits of various functional groups of proteins and polysaccharides of cyanobacterial biomass, involved in surface binding of Cd. The determination of catalase (CAT) activity in strain KO05 exposed to Cd (II) concentrations of 2, 5 and 10mgL showed an increase in enzyme activity after 24h exposure compared to unexposed cells. Correspondingly, CAT activity showed a significant decrease after 48h of treatment with Cd (II) concentrations of 5 and 10mgL. CAT activity was decreased significantly at all concentrations within 72h after exposure to Cd. On the contrary, while ascorbate peroxidase (APX) gave the expected lower activity compared to the CAT within 24h after Cd treatment, its activity lasted up to 72h. Limnothrix sp. KO05 cells treated with 5 and 10mgL Cd (II) over 72h exposure showed a reduction in chlorophyll a contents compared to the controls. However, following exposure to Cd, chlorophyll a and carotenoid contents is reduced and after overcoming stress and deployment of an adaptation mechanism, the amounts of these pigments is gradually increased in the cells. The reduction was slower for chlorophyll a pigment compared to carotenoids that may be an indication of the physiological importance of chlorophyll pigment for the phtosynthetic cells. Results related to lipid peroxidation in Limnothrix sp. KO05 represent a significant increase of MDA in the first 24h after exposure to the different concentrations of Cd (2, 5 and 10mgL). However, the MDA levels were decreased over time and no significant difference attained after 72h exposure to Cd concentrations of 2 and 10mgL compared to control.
在本研究中，我们从伊朗东阿塞拜疆省（伊朗西北部地区）不同受重金属污染的水环境中分离出五株本土蓝藻菌株。通过形态学和16S rRNA序列分析，将其中一株鉴定为Limnothrix sp. KO05，并因其具有最大的镉吸收潜力而被选作进一步研究对象。扫描电子显微镜（SEM）显示，Limnothrix sp. KO05蓝藻形成丝状结构，且在一定程度上呈直形或弯曲状。在Cd（II）浓度为150mg/L时，最大生物吸附容量为82.18±1.22mg/g。Langmuir吸附等温线表明其与实验数据拟合度较好。基于四个自变量的响应面法（RSM）显示，在最佳条件下预测的最大生物吸附效率为98.7%。经镉处理样品的傅里叶变换红外光谱（FT-IR）图谱证实了蓝藻生物质中蛋白质和多糖的各种官能团在镉的表面结合中发挥了作用。对暴露于2、5和10mg/L Cd（II）浓度下的KO05菌株中过氧化氢酶（CAT）活性的测定表明，与未暴露细胞相比，暴露24小时后酶活性增加。相应地，在用5和10mg/L Cd（II）处理48小时后，CAT活性显著下降。暴露于镉后72小时内，所有浓度下的CAT活性均显著降低。相反，虽然抗坏血酸过氧化物酶（APX）在镉处理后24小时内的活性预期低于CAT，但其活性持续长达72小时。在72小时的暴露过程中，用5和10mg/L Cd（II）处理的Limnothrix sp. KO05细胞与对照相比，叶绿素a含量降低。然而，暴露于镉后，叶绿素a和类胡萝卜素含量降低，在克服压力并启动适应机制后，细胞内这些色素的含量逐渐增加。与类胡萝卜素相比，叶绿素a色素的降低速度较慢，这可能表明叶绿素色素对光合细胞具有生理重要性。与Limnothrix sp. KO05中脂质过氧化相关的结果表明，在暴露于不同浓度的镉（2、5和10mg/L）后的最初24小时内，丙二醛（MDA）显著增加。然而，随着时间的推移，MDA水平下降，与对照相比，在暴露于2和10mg/L镉浓度72小时后没有显著差异。
