Reduction of selenite to Se(0) nanoparticles by filamentous bacterium Streptomyces sp. ES2-5 isolated from a selenium mining soil.

Rong Yao,Dan Wang,Yuanqing Tan,Gejiao Wang,Rui Wang,Shixue Zheng

doi:10.1186/s12934-016-0554-z

Abstract

BackgroundSelenium (Se) is an essential trace element in living systems. Microorganisms play a pivotal role in the selenium cycle both in life and in environment. Different bacterial strains are able to reduce Se(IV) (selenite) and (or) Se(VI) (selenate) to less toxic Se(0) with the formation of Se nanoparticles (SeNPs). The biogenic SeNPs have exhibited promising application prospects in medicine, biosensors and environmental remediation. These microorganisms might be explored as potential biofactories for synthesis of metal(loid) nanoparticles.ResultsA strictly aerobic, branched actinomycete strain, ES2-5, was isolated from a selenium mining soil in southwest China, identified as Streptomyces sp. based on 16S rRNA gene sequence, physiologic and morphologic characteristics. Both SEM and TEM-EDX analysis showed that Se(IV) was reduced to Se(0) with the formation of SeNPs as a linear chain in the cytoplasm. The sizes of the SeNPs were in the range of 50–500 nm. The cellular concentration of glutathione per biomass decreased along with Se(IV) reduction, and no SeNPs were observed in different sub-cellular fractions in presence of NADPH or NADH as an electron donor, indicating glutathione is most possibly involved in vivo Se(IV) reduction. Strain ES2-5 was resistant to some heavy metal(loid)s such as Se(IV), Cr(VI) and Zn(II) with minimal inhibitory concentration of 50, 80 and 1.5 mM, respectively.ConclusionsThe reducing mechanism of Se(IV) to elemental SeNPs under aerobic condition was investigated in a filamentous strain of Streptomyces. Se(IV) reduction is mediated by glutathione and then SeNPs synthesis happens inside of the cells. The SeNPs are released via hypha lysis or fragmentation. It would be very useful in Se bioremediation if Streptomyces sp. ES2-5 is applied to the contaminated site because of its ability of spore reproduction, Se(IV) reduction, and adaptation in soil.

Highlights

Selenium (Se) is an essential trace element in living systems
The reducing mechanism of Se(IV) to elemental Se nanoparticles (SeNPs) under aerobic condition was investigated in a filamentous strain of Streptomyces
Se(IV) reduction is mediated by glutathione and SeNPs synthesis happens inside of the cells

Summary

Introduction

Selenium (Se) is an essential trace element in living systems. Microorganisms play a pivotal role in the selenium cycle both in life and in environment. The biogenic SeNPs have exhibited promising application prospects in medicine, biosensors and environmental remediation. These microorganisms might be explored as potential biofactories for synthesis of metal(loid) nanoparticles. Selenium (Se) is an essential trace element for the adequate and healthy life of human, animal, bacterium and other living systems and has an uneven distribution in the Earth’s crust [1]. Diverse microorganisms are involved in the transformation of selenium from one oxidation state to another and play a pivotal role on the selenium biogeochemical cycle [4, 7, 8]. The biosynthesized SeNPs have been found applications in various fields including medicine as antimicrobial, antioxidant and anticancer agents [15,16,17,18], biosensors [19, 20] and environmental remediation [21,22,23]

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