Effect of Magnetite Nanoparticles Addition on Modification of Cobalamins Production via Propionibacterium freudenreichii PTCC1674 Using Oily Sludge of Lubricant Industry as a Carbon Source

Cobalamins are one of the most complicated cofactors produced by microorganisms. Propionibacterium freudenreichii has to follow the anaerobic and aerobic conditions respectively during a course of batch fermentation, for the production of the biologically active form of cobalamins. Magnetite (Fe3O4) nanoparticles can modify gas-liquid volumetric mass transfer coefficient in the fermentation system in order to create a more efficient aeration step. Initially, the modified production of Fe3O4 nanoparticles through the coprecipitation method was investigated, and the smallest size of nanoparticles was optimized to 13.86 nm via the Box-Behnken design of response to surface methodology (RSM). The optimum condition was present at the synthesis, including the temperature of 60 °C, reaction duration of 10 minutes, and the medium agitation speed of 700 rpm. Synthesized nanoparticles were characterized by SEM images, PXRD, and EDS analysis; additionally, the EDS spectrum reflects 39.33% of Fe and 51.8% of oxygen atomic distribution, which confirms the Fe3O4 nanoparticles synthesis. Magnetite nanoparticle suspension was added to the fermentation medium in order to compare the effects of nanoparticle incorporation and dimethylbenzimidazole addition on the cobalamin production via Propionibacterium freudenreichii. NPs incorporation in the fermentation broth was able to increase the cyanocobalamin production by 20%, while there was no incorporation of external DMBI in the medium. Finally, by the central composite design analysis, cyanocobalamin production from Propionibacterium freudenreichii fermentation was optimized to 1.548 mg.L-1. Oily sludge (as a new carbon source) of 4 %w/v, magnetite nanoparticles suspension of 7.5 %v/v, and the fermentation temperature of 37 °C caused the CCD optimum condition.