Aerobic biogenesis of selenium nanospheres by Bacillus cereus isolated from coalmine soil

Soniya Dhanjal,Swaranjit Cameotra

doi:10.1186/1475-2859-9-52

Abstract

BackgroundMicroorganisms that are exposed to pollutants in the environment, such as metals/metalloids, have a remarkable ability to fight the metal stress by various mechanisms. These metal-microbe interactions have already found an important role in biotechnological applications. It is only recently that microorganisms have been explored as potential biofactories for synthesis of metal/metalloid nanoparticles. Biosynthesis of selenium (Se0) nanospheres in aerobic conditions by a bacterial strain isolated from the coalmine soil is reported in the present study.ResultsThe strain CM100B, identified as Bacillus cereus by morphological, biochemical and 16S rRNA gene sequencing [GenBank:GU551935.1] was studied for its ability to generate selenium nanoparticles (SNs) by transformation of toxic selenite (SeO32-) anions into red elemental selenium (Se0) under aerobic conditions. Also, the ability of the strain to tolerate high levels of toxic selenite ions was studied by challenging the microbe with different concentrations of sodium selenite (0.5 mM-10 mM). ESEM, AFM and SEM studies revealed the spherical Se0 nanospheres adhering to bacterial biomass as well as present as free particles. The TEM microscopy showed the accumulation of spherical nanostructures as intracellular and extracellular deposits. The deposits were identified as element selenium by EDX analysis. This is also indicated by the red coloration of the culture broth that starts within 2-3 h of exposure to selenite oxyions. Selenium nanoparticles (SNs) were further characterized by UV-Visible spectroscopy, TEM and zeta potential measurement. The size of nanospheres was in the range of 150-200 nm with high negative charge of -46.86 mV.ConclusionsThis bacterial isolate has the potential to be used as a bionanofactory for the synthesis of stable, nearly monodisperse Se0 nanoparticles as well as for detoxification of the toxic selenite anions in the environment. A hypothetical mechanism for the biogenesis of selenium nanoparticles (SNs) involving membrane associated reductase enzyme(s) that reduces selenite (SeO32-) to Se0 through electron shuttle enzymatic metal reduction process has been proposed.

Highlights

Microorganisms that are exposed to pollutants in the environment, such as metals/metalloids, have a remarkable ability to fight the metal stress by various mechanisms
Microorganism and Growth Conditions The strain CM100B was isolated from coalmine soil by enrichment of the soil sample for one week with sodium selenite (0.5 mM) followed by standard method of dilution plating on tryptic soy agar (TSA) medium supplemented with 0.5 mM sodium selenite
Characterization of selenite tolerant bacterium isolated from coalmine soil Selenium is a very coalphile element, having strong affinity to organic and inorganic matter present in coals

Summary

Introduction

Microorganisms that are exposed to pollutants in the environment, such as metals/metalloids, have a remarkable ability to fight the metal stress by various mechanisms These metal-microbe interactions have already found an important role in biotechnological applications. Amorphous selenium nanoparticles (SNs) possess unique photoelectric, semiconducting and X-ray-sensing properties These nanoparticles show biological activity and good adsorptive ability due to interaction between the nanoparticles and NH, C = O, COO_ and C-N groups of proteins [2]. There has been increasing interest in synthesis of nanoparticles using biological systems leading to the development of various biomimetic approaches. Microorganisms, such as bacteria, yeast and fungi play an important role in recycling of minerals in the environment. The toxicity of metal ions is reduced or eliminated by changing the redox state of the metal ions and in the process leading to the formation of well-defined nanoscale particles in some cases [9]

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Conclusion