Institute of Biology for Engineers and Biotechnology of Wastewater, Karlsruhe Institute of Technology, 76131, Karlsruhe, Germany.
Microb Cell Fact. 2012 Jul 9;11:64. doi: 10.1186/1475-2859-11-64.
Selenium (Se) is an essential trace element, but is toxic at high concentrations. Depending upon the geological background, the land use or on anthropogenic pollution, different amounts of Se may be present in soil. Its toxicity is related to the oxyanions selenate and selenite as they are water soluble and bioavailable. Microorganisms play an important role in Se transformations in soil and its cycling in the environment by transforming water-soluble oxyanions into water insoluble, non-toxic elemental Se (0). For this study, soil samples were collected from selenium-contaminated agricultural soils of Punjab/India to enrich and isolate microbes that interacted with the Se cycle.
A mixed microbial culture enriched from the arable soil of Punjab could reduce 230 mg/l of water soluble selenite to spherical Se (0) nanoparticles during aerobic growth as confirmed by SEM-EDX. Four pure cultures (C 1, C 4, C 6, C 7) of Gram negative, oxidase and catalase positive, aerobic bacteria were isolated from this mixed microbial consortium and identified by 16 S rDNA gene sequence alignment as two strains of Duganella sp. (C 1, C 4) and two strains of Agrobacterium sp.(C 6, C 7). SEM/TEM-EDX analyses of the culture broth of the four strains revealed excretion of uniformly round sharply contoured Se (0) nanoparticles by all cultures. Their size ranged from 140-200 nm in cultures of strains C 1 and C 4, and from 185-190 nm in cultures of strains C 6 and C 7. Both Duganella sp. revealed better selenite reduction efficiencies than the two Agrobacterium sp.
This is the first study reporting the capability of newly isolated, aerobically growing Duganella sp. and Agrobacterium sp. from soils of Punjab/India to form spherical, regularly formed Se (0) nanoparticles from water soluble selenite. Among others, the four strains may significantly contribute to the biogeochemical cycling of Se in soil. Bioconversion of toxic selenite to non-toxic Se (0) nanoparticles under aerobic conditions in general may be useful for detoxification of agricultural soil, since elemental Se may not be taken up by the roots of plants and thus allow non-dangerous fodder and food production on Se-containing soil.
硒（Se）是一种必需的微量元素，但在高浓度下是有毒的。根据地质背景、土地利用或人为污染的不同，土壤中可能含有不同量的硒。其毒性与含氧阴离子硒酸盐和亚硒酸盐有关，因为它们水溶性和生物可利用。微生物在土壤中硒的转化及其在环境中的循环中起着重要作用，通过将水溶性含氧阴离子转化为不溶性、无毒的元素硒（0）。为此，本研究从旁遮普邦受硒污染的农业土壤中采集土壤样本，以富集和分离与硒循环相互作用的微生物。
从旁遮普邦耕地中富集的混合微生物培养物在有氧生长过程中可以将 230mg/L 的水溶性亚硒酸盐还原为球形硒（0）纳米颗粒，这一点通过 SEM-EDX 得到证实。从该混合微生物联合体中分离出 4 株革兰氏阴性、氧化酶和过氧化氢酶阳性、需氧细菌的纯培养物（C1、C4、C6、C7），并通过 16S rDNA 基因序列比对鉴定为两株 Duganella sp.（C1、C4）和两株 Agrobacterium sp.（C6、C7）。对 4 株菌的培养液进行 SEM/TEM-EDX 分析表明，所有培养物均分泌均匀圆形、轮廓分明的硒（0）纳米颗粒。它们的大小范围为菌株 C1 和 C4 的培养物中为 140-200nm，菌株 C6 和 C7 的培养物中为 185-190nm。 Duganella sp. 的亚硒酸盐还原效率均优于两株 Agrobacterium sp.。
这是首次报道从印度旁遮普邦土壤中分离出的、需氧生长的 Duganella sp.和 Agrobacterium sp.能够从水溶性亚硒酸盐形成球形、规则形成的硒（0）纳米颗粒。此外，这 4 株菌可能会显著促进土壤中硒的生物地球化学循环。在有氧条件下将有毒的亚硒酸盐转化为无毒的硒（0）纳米颗粒通常可用于农业土壤的解毒，因为元素硒可能不会被植物根系吸收，从而允许在含硒土壤上进行无危险的饲料和食物生产。
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