胞外聚合物对三角褐指藻砷酸盐富集和形态转化的影响

Effects of extracellular polymeric substances on the accumulation and transformation of As(Ⅴ)by Phaeodactylum tricornutum

微生物分泌的胞外聚合物(EPS)对重金属吸附有重要作用,然而EPS对硅藻生长及砷(As)的富集和转化有何影响尚不清楚。为此本文选取三角褐指藻,研究了不同浓度砷酸盐(As(Ⅴ))处理下EPS各组分含量、藻细胞生长以及细胞形貌的变化,并比较了EPS提取前后藻细胞对砷的富集和形态转化的差异。结果表明,三角褐指藻对As(Ⅴ)有一定的耐性,72 h的EC10值为1.75 mg·L^(−1)。随着As(Ⅴ)浓度的升高,EPS的分泌量呈增加的趋势,最大可达到对照组的1.47倍。藻细胞吸收As(Ⅴ)后,转化为亚砷酸盐(As(Ⅲ))、二甲基砷(DMA)和一甲基砷(MMA)并外排至培养液,EPS能促进藻细胞对As(Ⅴ)的富集、还原和甲基化。衰减全反射傅里叶变换红外光谱(ATR-IR)数据表明,EPS中存在—OH、—NH、C—O—C等官能团,增加了藻细胞对砷的吸附,从而限制了As的跨膜运输。总之,EPS增强了三角褐指藻对As(Ⅴ)的耐性、富集和形态转化。研究结果可为利用硅藻EPS治理水体As污染提供理论依据。

Extracellular polymeric substances(EPS)secreted by microorganisms play an important role in the adsorption of heavy metals.However,effects of EPS on the accumulation and transformation of arsenic(As)in diatoms are still unclear.As such,Phaeodactylum tricornutum was selected to study the variations in the composition of EPS,growth and morphology of algal cells under different treatments of arsenate(As(Ⅴ)).Besides,the accumulation and transformation of As by algae cells before and after EPS extraction were compared.The results showed that P.tricornutum had certain tolerance to As(Ⅴ),and the EC10 value at 72 h was 1.75 mg·L^(−1).With the increase of As(Ⅴ)concentration,the secretion of EPS showed an increasing trend,which maximally reached 1.47 times higher than those of the control group.Arsenate(As(Ⅴ))absorbed into the cells was converted into arsenite(As(Ⅲ)),dimethyl arsenic(DMA)and monomethyl arsenic(MMA),which were then released into the culture medium.The EPS also promoted the As(Ⅴ)accumulation,reduction and methylation by the algae cells.At the same time,ATR-IR data confirmed the presence of—OH,—NH and C—O—C functional groups,which increased the extracellular adsorption of As by algal cells and thereby limited the As transport across membrane.In summary,EPS promoted the As(Ⅴ)tolerance,accumulation and transformation by P.tricornutum to As(Ⅴ).The results of this study may provide a theoretical basis for remediation of As pollution in water bodies using diatom EPS.