Mycobacterium bovis (M. bovis) is a slow-growing bacteria that can intracellularly reduce selenium ions to elemental selenium nanoparticles (SeNPs). We used bacterial lysates along with vitamin C to help the synthesis of SeNPs coated with M. bovis Bacille Calmette-Guérin (BCG) crude hydrophobic materials. However, the large-scale fabrication, separation, extraction, and purification of intercellular SeNPs which are prepared by using M. bovis, have many complexities. So, we developed a simple method for preparation of above BCG-coated nanoparticles and tested its potential immune-modulatory effects. In the current investigation, we cultivated the M. bovis in conventional media and prepared total cell lysates from this bacterium by just applying freeze and thaw and ultra-sonication. The resulting cell lysates were added to the solution containing selenium ions before adding the ascorbic acid as a reducing agent. At the end of the process, the fabricated selenium nanoparticles were separated by centrifugation and characterized by different instrumentation methods. In the next step, to evaluate the immune-modulatory effects of the hepatitis B surface antigen (HBsAg) vaccine alone, and in combination with plain SeNPs or SeNPs-BCG lysate, the serum level of interferon-gamma (IFN-γ) was determined in different groups by enzyme-linked immunosorbent assay (ELISA). This study showed adjuvant effects of prepared nanoparticles (in both 10 μg/300 μL and 100 μg/300 μL doses) in increasing the level of interferon-gamma (IFN-γ) in comparison with vaccine alone. Moreover, in both doses of SeNPs-BCG lysate, the level of interferon-gamma (IFN-γ) was remarkably higher than the same doses of plain SeNPs. As a result, synthesized SeNPs in the presence of whole-cell lysates of M. bovis indicated a greater ability to induce the interferon-gamma (IFN-γ) compared with other groups. Additionally, its easy fabrication procedure can be considered its superiority.

Many bacteria are potential to reduce the metal ions to elemental nanoparticles and are able to grow in the presence of these inorganic compounds. Whole bacterial cells suspended in aqueous media can also convert some soluble metal ions into elemental nanomaterials. In this study, the reduction of different concentrations of selenium ions was investigated using various amounts of Bacillus sp. MSh-1 whole cell biomass, with the aim of increasing the yield of selenium nanoparticles. The MSh-1 test strain used in this study was previously isolated from the Caspian Sea (north of Iran) which can produce selenium nanoparticles. Reduction of selenium ions by whole Bacillus sp. MSh-1 cells in normal saline had a close relation between the ratio of applied biomass and the selenium ion concentration, as no considerable reduction was detected in the ratios lower than 1 gram of biomass for each 100 mg of selenium. Neither compounds of piperitone nor glucose had positive effects on selenium reduction by Bacillus sp. MSh-1. It also should be mentioned that Se NPs were not efficiently produced even after 20 hours and 32 hours, respectively.