Abstract
The wide anthropogenic use of selenium compounds represents the major source of selenium pollution worldwide, causing environmental issues and health concerns. Microbe-based strategies for metal removal/recovery have received increasing interest thanks to the association of the microbial ability to detoxify toxic metal/metalloid polluted environments with the production of nanomaterials. This study investigates the tolerance and the bioconversion of selenite (SeO32−) by the aerobically grown Actinomycete Rhodococcus aetherivorans BCP1 in association with its ability to produce selenium nanoparticles and nanorods (SeNPs and SeNRs). The BCP1 strain showed high tolerance towards SeO32− with a Minimal Inhibitory Concentration (MIC) of 500mM. The bioconversion of SeO32− was evaluated considering two different physiological states of the BCP1 strain, i.e. unconditioned and/or conditioned cells, which correspond to cells exposed for the first time or after re-inoculation in fresh medium to either 0.5 or 2mM of Na2SeO3, respectively. SeO32− bioconversion was higher for conditioned grown cells compared to the unconditioned ones. Selenium nanostructures appeared polydisperse and not aggregated, as detected by electron microscopy, being embedded in an organic coating likely responsible for their stability, as suggested by the physical-chemical characterization. The production of smaller and/or larger SeNPs was influenced by the initial concentration of provided precursor, which resulted in the growth of longer and/or shorter SeNRs, respectively. The strong ability to tolerate high SeO32− concentrations coupled with SeNP and SeNR biosynthesis highlights promising new applications of Rhodococcus aetherivorans BCP1 as cell factory to produce stable Se-nanostructures, whose suitability might be exploited for biotechnology purposes.
Highlights
IntroductionSelenium (Se) is present in the earth crust as a rare element or associated in minerals (e.g., crooksite and calusthalite), with concentrations ranging from 0.01 to 1200 mg/kg [1,2,3]
Selenium (Se) is present in the earth crust as a rare element or associated in minerals, with concentrations ranging from 0.01 to 1200 mg/kg [1,2,3]
Gram-positive bacteria belonging to the Bacillus genus have been noted for their ability to grow in the presence of either SeO42− or SeO32−, including Bacillus mycoides SelTE01, Bacillus cereus CM100B and Bacillus selenitireducens MLS10
Summary
Selenium (Se) is present in the earth crust as a rare element or associated in minerals (e.g., crooksite and calusthalite), with concentrations ranging from 0.01 to 1200 mg/kg [1,2,3]. It is an essential micronutrient for living systems, being present as seleno-cysteine in at least 25 human selenoproteins [4]. Se2− present in organic compounds (e.g. dimethyl selenide, trimethyl selenonium, selenomethionine, selenocysteine and Se-methylselenocysteine) and Se0 showed lower toxicity levels [7,8,9] compared to SeO42− and SeO32−, which were described as the most toxic, soluble and, bioavailable forms. Gram-positive bacteria belonging to the Bacillus genus have been noted for their ability to grow in the presence of either SeO42− or SeO32−, including Bacillus mycoides SelTE01, Bacillus cereus CM100B and Bacillus selenitireducens MLS10
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