In the present study, Authors analyse dynamics of growth, selenite reduction rate and elemental selenium formation in cultures of Stenotrophomonas maltophilia, strain SeITE02, originally isolated from the rhizosphere of the Se hyperaccumulator legume Astragalus bisulcatus, grown in a seleniferous soil. Selenium nanoparticles synthesized by S. maltophilia SeITE02 were tested for their possible antibacterial activity against Staphylococcus aureus ATTC25923 and Pseudomonas aeruginosa PAO1 grown either as planktonic cells or in biofilm mode