Application of the luminous bacterium Photobacterium phosphoreum for toxicity monitoring of selenite and its reduction to selenium(0) nanoparticles

Luminous marine bacteria are traditionally used as a bioassay due to the convenience and high rate of registering the intensity of their physiological function - luminescence. This study aimed to develop the application of Photobacterium phosphoreum in traditional and novel fields - toxicity monitoring and biotechnology. We demonstrated (1) effects of selenite ions on bioluminescence, and (2) biotransformation of selenite to selenium(0) in the form of nanoparticles. The effects of selenite (SeO₃^2-) on the intensity of bacterial bioluminescence were studied, and its dependencies on exposure time and concentration of Na₂SeO₃ were analyzed. Bioluminescence activation and inhibition were revealed; dose-effect dependencies corresponded to the hormesis model. The toxicity of SeO₃^2- was characterized by an effective concentration of 10^-3 M. Effects of SeO₃^2- on reactive oxygen species (ROS) in bacterial suspensions were studied. High positive correlations were found between the bioluminescence intensity and ROS content, which indicates the decisive role of ROS and associated redox processes in the bioeffects of selenite ions. Scanning and transmission electron microscopy revealed the presence of nano-structures in the bacteria exposed to selenite. The energy dispersion spectrum detected a high content of selenium in the nanoparticles. The particle size distribution depended on Na₂SeO₃ concentration; maxima of the distribution varied within 45-55 nm.