Effect of magnetite nanoparticles addition on modification of cobalamins production via Propionibacterium freudenreichii PTCC1674 using oily sludge of lubricant industry as the carbon source

Cobalamins are one of the most complicated cofactors produced by the 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 to create more efficient aeration step. Initially, the modified production of Fe3O4 nanoparticle through coprecipitation method was investigated, and the smallest size of nanoparticles optimized to 13.86 nm via Box-Behnken design of response to surface methodology (RSM). The optimum condition was at the synthesis temperature of 60 °C, reaction duration of 10 minutes, and the medium agitation speed of 700 rpm. Synthesized nanoparticles characterized by SEM images, PXRD and EDS analysis while EDS spectrum reflects 39.33% of Fe and 51.8% of oxygen atomic distribution, which confirms Fe3O4 nanoparticles synthesis. Magnetite nanoparticle suspension added to the fermentation medium to compare the effect of nanoparticles incorporation and dimethylbenzimidazole addition on the cobalamin production via Propionibacterium freudenreichii. NPs incorporation in the fermentation broth was able to increase 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 to CCD optimum condition.