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生物膜通常存在于水生系统中,其内存在水通道,水是饱和生物膜中关键的运输介质[1]。生物膜存在形式相比于游离态的细胞能更好地抵抗重金属的毒性[2]。然而,受重金属和其他污染物污染的土壤大多与非饱和生物膜有关[3]。非饱和生物膜内的传质与饱和生物膜内的传质有很大的不同,其内没有水通道[4]。此外,非饱和环境中的水以及土壤的物理化学性质将直接影响生物膜中微生物的生存和代谢活动。非饱和生物膜通常以细胞和微生物分泌的胞外聚合物(EPS)连接而成[5],这也是自然界最常见的细菌生长形式[6]。
胞外聚合物(EPS)主要由蛋白质、多糖以及少量核酸组成,在细菌抵抗外界环境胁迫中起着非常重要的作用[7]。EPS的产生可以形成一种含水微环境,有助于维持细胞环境的稳态,从而保护细胞免受环境压力和有毒物质的胁迫[8]。Zhang等[9]认为,EPS中多糖的增加是细菌抵抗高盐度胁迫的一种保护机制。Sheng等[10]发现,胞外蛋白的增加可以保护细胞免受有毒物质的侵害。EPS还能结合有毒重金属保护细胞免受有毒重金属的胁迫[11]。Sharma等[12]报道了细胞胞外沉淀是木糖氧化无色杆菌去除铅的主要机制。Hou等[13]也证实了EPS在Cu2+固定化中起着关键的作用。以往的研究都集中在饱和环境中环境压力和污染物对EPS的影响,虽然在土壤非饱和生物膜中EPS可能会出现类似的影响,但是EPS的产生和组成取决于生长条件[14]。因此,了解非饱和环境中环境压力和污染物对EPS的影响是生物修复技术的一个重要任务。
研究表明,Shewanella putrefaciens CN32能够降解多种重金属,并能够调节土壤中重金属的迁移[15-17]。本研究选择Shewanella putrefaciens CN32模拟在非饱和环境中生长的生物膜,探究在不同pH、温度、渗透压条件下非饱和生物膜的胞内外大分子物质的产生和组成变化。再将非饱和生物膜暴露于重金属铬,研究非饱和生物膜对铬的结合作用以及结合机理。
Shewanella putrefaciens CN32非饱和生物膜对环境压力的响应以及与铬的作用
Responses of Shewanella putrefaciens CN32 unsaturated biofilms to environmental stress and interaction with chromium
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摘要: Shewanella putrefaciens CN32模拟在非饱和环境中生长的生物膜,探究不同环境条件对非饱和生物膜胞内外大分子物质的影响,以及生物膜对重金属Cr的作用。在84 h、219 mmol·L−1 NaCl、pH 6.2和35 ℃条件下,生物膜分泌胞外聚合物的量达到最大,每片生物膜胞外聚合物总量为400.6 μg;生长12 h的每片生物膜中胞外聚合物吸附了9.77 μg Cr,占生物膜总吸附量的63.8%;三维荧光光谱表明,生物膜吸附Cr后胞外聚合物中色氨酸蛋白类物质与酪氨酸蛋白类物质荧光强度明显降低。结果表明,一定强度的渗透压、低pH和高温能促进生物膜分泌更多的胞外聚合物。非饱和生物膜中,胞外聚合物是重金属Cr的主要结合区域,并且胞外聚合物中的色氨酸蛋白类物质与酪氨酸蛋白类物质可能在与Cr络合中起重要作用。Abstract: Shewanella putrefaciens CN32 was selected to simulate the biofilm growing in unsaturated environment. The influence of different environmental factors on the extracellular and intracellular macromolecular substances of unsaturated biofilms, as well as the interactions between the unsaturated biofilms and heavy metal Cr were explored. Under the conditions of 84 h, 219 mmol·L−1 NaCl, pH 6.2 and 35°C, the extracellular polymeric substances (EPS) secreted by biofilms reached the maximum content of 400.6 μg per biofilm. The EPS in each biofilm grown for 12 h adsorbed 9.77 μg Cr, accounting for 63.8% of the total amount of the adsorbed Cr. Three-dimensional fluorescence spectroscopy shows that the fluorescence intensities of tryptophan and tyrosine proteins in the EPS was significantly reduced after Cr adsorption. In addition, a certain strength of osmotic pressure, low pH and high temperature could promote the EPS secretion by the biofilms. The EPS in the unsaturated biofilms were the main binding area of Cr, and the tryptophan and tyrosine proteins were suggested to play an important role in the complexation between biofilms and Cr.
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Key words:
- unsaturated biofilms /
- Cr /
- extracellular polymeric substances /
- complexation
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