Abstract
Selenium (Se) is an essential element for the cell that has multiple applications in medicine and technology; microorganisms play an important role in Se transformations in the environment. Here we report the previously unidentified ability of the soil bacterium Pseudomonas putida KT2440 to synthesize nanoparticles of elemental selenium (nano-Se) from selenite. Our results show that P. putida is able to reduce selenite aerobically, but not selenate, to nano-Se. Kinetic analysis indicates that, in LB medium supplemented with selenite (1 mM), reduction to nano-Se occurs at a rate of 0.444 mmol L−1 h−1 beginning in the middle-exponential phase and with a final conversion yield of 89%. Measurements with a transmission electron microscope (TEM) show that nano-Se particles synthesized by P. putida have a size range of 100 to 500 nm and that they are located in the surrounding medium or bound to the cell membrane. Experiments involving dynamic light scattering (DLS) show that, in aqueous solution, recovered nano-Se particles have a size range of 70 to 360 nm. The rapid kinetics of conversion, easy retrieval of nano-Se and the metabolic versatility of P. putida offer the opportunity to use this model organism as a microbial factory for production of selenium nanoparticles.
Highlights
To date, the crucial components of the global process of biotransformation have not been completely elucidated
It is thought that the reduction of selenium oxyanions involves two steps: first selenate is reduced to selenite and selenite is reduced to elemental selenium
Selenite is transformed into selenium, SeO3−2 → Se0, by the following mechanism[28]: (i) selenite becomes chelated first by thiol-containing molecules such as glutathione, leading to the production of selenodiglutathione. (ii) this compound is the substrate of the enzyme glutathione reductase that produces unstable intermediates eventually converted to elemental selenium
Summary
To test whether P. putida is capable of reducing aerobically selenate and selenite to elemental selenium, we performed growth experiments in rich medium (LB; Fig. 1) and minimal medium (M9, citrate 0.2% w/v; data not shown) in the presence and absence of each oxyanion SeO3−2 or SeO4−2 (1 mM). Because of the differences between cell growth rates in rich (LB) and minimal media (M9 citrate), red elemental selenium appeared in LB after culturing for 15 h, whereas in M9 citrate it occurred after nearly 72 h (data not shown) For this reason, and due to the inability of P. putida to reduce selenate, we focused the following experiments exclusively on the reduction of selenite in LB. This property makes P. putida more suitable to catalyse reduction processes such as the synthesis of selenium from selenite
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
