Comparison of Cerium Nanoparticles Toxicity against Bacillus subtilis Grown in Two Different Types of Biofilm

New chemicals including nanomaterials are being created and spread at high speed. In the E.U., REACH compliance imposes to manufacturers some tests but they are limited. Often, they cannot detect anything if the cells or organisms are able to overcome the toxic effect at the macroscopic level, preventing the suspicion of a potential long-term effect. Concerning bacteria that are essential for ecosystems and human health (microbiota), they are often considered as a whole in a consortium and only global parameters are measured. To overcome these limitations, we performed a study on the essential soil bacterium Bacillus subtilis. Two types of biofilm that are closer to its natural growth mode (particularly around plant roots) than the usual liquid type culture have been assayed: pellicle biofilm and swarming. We then used the power of shotgun proteomics to analyze in details these two somehow similar modes of cultures. Several physiological and metabolic patterns including proteins implicated in sporulation have shown significant differences. The effect of two types of nanoparticles (silicon and cerium oxide nanoparticles) has then been studied in the same way. This allowed us to investigate in details the response of the bacteria and focus on the differences observed depending on the biofilm type. This clearly highlighted the importance of testing several growth conditions and pinpointed the power of proteomics.