Background: Microorganisms commonly employed in food industry, such as Lactobacillus
plantarum and Saccharomyces cerevisiae, are also excellent natural nanotechnologists. They
reduce selenite (SeO3
2-) to form nanoparticles of red selenium (Se) of exceptional quality and with
interesting physical and (bio-)chemical properties.
Objectives: The production of these nanoparticles has been studied in several relevant microorganisms
to gain a better picture of the overall properties and quality of these particles, possible differences
between producers, ease of production and, in particular, biological activity.
Methods: Several common microorganisms, namely L. plantarum, S. cerevisiae and E. coli have
been cultured under standard conditions and 1 mM concentrations of SeO2 have been converted into
red particles of elemental selenium. These particles are characterized extensively with respect to
uniformity, size, shape, consistency and, in particular, biological activity against infectious microbes.
Results: Highly uniform amorphous spherical particles of 100 nm to 200 nm in diameter could be
produced by several microorganisms, including Lactobacillus. Although originating in bacteria and
yeast, these particles exhibit antimicrobial activity when employed at concentrations of around 100
μM. This activity may in part be due to the inherent chemistry of selenium and /or of the protein
coating of the particles. Interestingly, yeast also forms larger rod-like structures. These micro-needles
with around 85 nm in diameter and up to 3 μm in length exhibit considerable antibacterial activity,
possibly resulting from additional, physical interactions with cellular structures.
Conclusion: Common microorganisms traditionally employed in the preparation of food produce
nanoparticles of selenium which may be harvested and explored as natural antimicrobial agents or
antioxidants. These particles provide a fine example of natural nanotechnology with biological activity
and applications in the food and food supplementation, medicine, agriculture and cosmetics.