Biogenic selenium and tellurium nanoparticles synthesized by environmental microbial isolates efficaciously inhibit bacterial planktonic cultures and biofilms

The present study deals with Se ⁰- and Te ⁰-based nanoparticles bio-synthesized by two selenite- and tellurite-reducing bacterial strains, namely Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1, isolated from polluted sites. We evidenced that, by regulating culture conditions and exposure time to the selenite and tellurite oxyanions, differently sized zero-valent Se and Te nanoparticles were produced. The results revealed that these Se ⁰ and Te ⁰ nanoparticles possess antimicrobial and biofilm eradication activity against Escherichia coli JM109, Pseudomonas aeruginosa PAO1, and Staphylococcus aureus ATCC 25923. In particular, Se ⁰ nanoparticles exhibited antimicrobial activity at quite low concentrations, below that of selenite. Toxic effects of both Se ⁰ and Te ⁰ nanoparticles can be related to the production of reactive oxygen species upon exposure of the bacterial cultures. Evidence so far achieved suggests that the antimicrobial activity seems to be strictly linked to the dimensions of the nanoparticles: indeed, the highest activity was shown by nanoparticles of smaller sizes. In particular, it is worth noting how the bacteria tested in biofilm mode responded to the treatment by Se ⁰ and Te ⁰ nanoparticles with a susceptibility similar to that observed in planktonic cultures. This suggests a possible exploitation of both Se ⁰ and Te ⁰ nanoparticles as efficacious antimicrobial agents with a remarkable biofilm eradication capacity.