耐盐希瓦氏菌异化还原铁过程中胞外聚合物的光谱分析

Spectral Analysis of Extracellular Polymers During Iron Dissimilar Reduction by Salt-Tolerant Shewanella Aquimarina

微生物的生长代谢往往受盐度的影响,因此筛选出耐盐性强的菌株对含盐废水的生物处理意义重大。选取一株从海洋分离具备耐盐异化金属还原的功能细菌(DMRB)——耐盐希瓦氏菌(Shewanella aquimarina XMS-1)作为研究对象,探究盐度对XMS-1还原Fe^(3+)过程及胞外聚合物变化的影响。考察了不同盐度下XMS-1的Fe^(3+)还原能力和胞外聚合物(EPS)的含量,并采用三维荧光光谱(3D-EEM)、拉曼光谱(Raman spectra)、红外光谱(FTIR)及其对应的二维相关光谱(2D-COS)分析了XMS-1还原Fe^(3+)过程中EPS的变化。结果表明,蛋白为XMS-1 EPS中主要物质,占EPS含量的80%以上,多糖的含量相对较少,3%盐度条件下会促进XMS-1的EPS产量,表明XMS-1在高盐环境中会分泌更多的EPS来保护细胞进行正常的生理活动。Fe^(3+)还原过程在盐度为1%~4%时得到促进,而在盐度高于5%时则受到抑制,过高盐度会抑制XMS-1的生长,导致Fe^(3+)还原率下降,其中3%盐度下Fe^(3+)还原率最高可达44.1%,相对于对照组增加了2.18倍。FTIR和Raman光谱结果显示XMS-1 EPS中含有羧基、羟基、氨基和羰基等金属离子氧化还原功能基团,其中3%盐度下EPS中蛋白酰胺类和多糖类代表峰增强,蛋白酰胺类代表峰变化显著,含O-和N-基团参与了Fe^(3+)还原过程。此外3D-EEM结果显示,Fe^(3+)还原过程结束后,EPS中色氨酸和酪氨酸两种荧光组分强度均下降,结合2D-COS光谱结果分析,发现色氨酸类蛋白在Fe^(3+)还原过程中先发生了显著变化,表明这两种荧光组分参与了Fe^(3+)的还原过程,其中色氨酸类蛋白在还原过程中作用更强。本研究不仅丰富了对耐盐菌EPS胞外电子转移过程的认识,也突出了EPS在自然环境中铁氧化还原转化的意义。

The growth and metabolism of microorganisms are often affected by salinity,so screening the salt-tolerant strains is of great significance for the biological treatment of saline wastewater.In this paper,Shewanella aquimarina XMS-1,a marine strain with salt tolerant metal reduction function(DMRB),was selected as the research object to explore the effects of salinity on the reduction process of Fe3+and the changes of extracellular polymers.The Fe3+reduction ability of XMS-1and the extracellular polymer(EPS)content under different salinity were investigated.Furthermore,Three dimensional fluorescence excitation-emission(3D-EEM),Raman spectra(Raman),Fourier transform infrared spectroscopy(FTIR),and Twodimensional correlation spectroscopy(2D-COS)were used to analyze the changes in extracellular polymers during the reduction of Fe3+by XMS-1.The results show that protein is the main substance in XMS-1EPS,accounting for more than 80%of EPS content,and polysaccharide content is relatively small.3%salinity conditions promote EPS production.XMS-1will secrete more EPS in the high salt environment to protect cells from normal physiological activities.The reduction process of Fe3+is accelerated at the salinity of 1%~4%,but is inhibited when the salinity is higher than 5%.Too high salinity would inhibit the growth of XMS-1,resulting in the decrease of the Fe3+reduction rate.The reduction rate of Fe3+was increased by 2.18times and reached 44.1%at the salinity of 3%.FTIR and Raman spectra showed that XMS-1EPS contained metal ion redox functional groups such as carboxyl,hydroxyl,amino and carbonyl.The peaks of protein amides and polysaccharides in EPS were enhanced at 3%salinity,and the representative peaks of protein amides changed significantly.The O-and N-groups were effective redox groups in Fe3+reduction.In addition,the Three-dimensional fluorescence results showed that after the Fe3+reduction process,the intensities of the two fluorescent components of tryptophan and tyrosine in EPS decreased.Combined with the analysis of 2D-COS spectral results,it was found that tryptophan-like proteins changed significantly during the reduction of Fe3+,indicating that the two fluorescent components were involved in the reduction process of Fe3+,and tryptophan-like proteins played a stronger role in the reduction process.This study enriched the understanding of the extracellular electron transfer process of EPS in halophilic bacteria,and highlighted the significance of EPS in iron redox transformation in natural environment.