Abstract <p>The bacterium <i>Azospirillum thiophilum</i> found in a sulfide-bearing spring (described by Lavrinenko et al. Int J Syst Evol Microbiol 60:2832–2837, 2010) is reported to be able to reduce Se^VI oxyanions (SeO₄^2–; selenate) in static conditions, representing microaerobic environments that are characteristic of many bacteria of the genus <i>Azospirillum</i>, forming selenium(0) nano-sized spheres (Se⁰-NSs). Their presence, resulting in a brick-red tint of the sediments of bacterial cells (at SeO₄^2– concentrations from 1 to 15 mM), was confirmed by TEM as nano-sized spheres within the bacterial cell biomass. Raman spectroscopic studies of the cell sediment samples obtained by static cultivation with SeO₄^2– exhibited an intensive Raman line at ca. 248&#xa0;cm^–1 with an increased linewidth, which is characteristic of amorphous elemental selenium(0) in its nano-sized structures. This is the first demonstration of the ability of an <i>Azospirillum</i> species (observed so far for <i>A. thiophilum</i> only) to reduce selenate to selenium(0). Noteworthy is that this process occurs in contact with air, which is accompanied by the formation of Se⁰-NSs of amorphous nature. Hence this ability of strain <i>A. thiophilum</i> BV-S to detoxify selenate (as the most toxic, well soluble and therefore mobile inorganic selenium chemical species) to non-soluble and non-toxic SeNPs is of clear environmental value.</p> Graphical abstract <p></p>