Effect of iron nanoparticles synthesized by a sol-gel process on Rhodococcus erythropolis T902.1 for biphenyl degradation

Nanoparticles (NPS) are considered as a new generation of compounds to improve environmental
remediation and biological processes. The aim of this study is to investigate the effect of iron NPS
encapsulated in porous silica (SiO2) on the biphenyl biodegradation by Rhodococcus erythropolis
T902.1 (RT902.1). The iron NPS (major iron oxide FexOy form) were dispersed in the porosity of a
SiO2 support synthesized by sol-gel process. These Fe/SiO2 NPS offer a stimulating effect on the
biodegradation rate of biphenyl, an organic pollutant that is very stable and water-insoluble. This
positive impact of NPS on the microbial biodegradation was found to be dependent on the NPS
concentration ranging from 10−6 M to 10−4 M. After 18 days of incubation the cultures containing
NPS at a concentration of 10−4 M of iron improved RT902.1 growth and degraded 35% more biphenyl than those without NPS (positive control) or with the sole SiO2 particles. Though the microorganism could not interact directly with the insoluble iron NPS, the results show that about
10% and 35% of the initial 10−4 M iron NPS encapsulated in the SiO2 matrix would be incorporated inside or adsorbed on the cell surface respectively and 35% would be released in the supernatant.
These results suggest that RT902.1 would produce siderophore-like molecules to attract iron from
the porous silica matrix.