Insights on the synthesis of iron-oxide nanoparticles and the detection of iron-reducing genes from soil microbes

This study explores the potential of some soil bacteria in the synthesis of iron oxide nanoparticles (IONPs), highlighting their advantages in terms of iron uptake and tolerance capacity. Soil samples collected from a metal fabricating workshop were successively screened in nutrient broth containing 1% iron salts (Fe₂O₃, FeCl_3, and FeSO₄) following a standard microbiological sampling technique. The recovered bacterial isolates (persister cells) were identified using polymerase chain reaction (PCR) and 16S rRNA sequencing. Ten bacterial isolates identified as Sporosarcina luteola, Bacillus badius (2), Bacillus subtilis (2), Bacillus tropicus, Bacillus cereus, Klebsiella pneumoniae, Klebsiella quasipneumoniae and Klebsiella africana were recovered. The method reports that six of the bacterial isolates extracellularly synthesize IONPs and the result from the energy dispersion x-ray (EDX) spectral analysis indicated varying weight percentages of bio-reduced iron by Bacillus subtilis-A12 (48.59%), Klebsiella quasipneumoniae (39.99%), Bacillus subtilis-B1 (39.97%), Bacillus cereus (38.62%), Bacillus badius (33.79%) and Klebsiella africana (32.61%). The IONPs exhibited absorbance peaks in the range of 250–350 nm, with a mean area size estimated between 31–72 nm using ImageJ software. Additionally, the presence of iron reductase (fhu) and cysteine desulfurase (suf) genes were detected in the recovered Bacillus and Klebsiella species through PCR analysis. This study has provided valuable insights into the physiology and genomic functions essential for microbial synthesis of IONPs and their relevance to nano-bioremediation.