Influence of carbon sources and biosurfactants on selenite and lead bioremediation by Enterococcus sp

• Explored the bioremediation potential of Enterococcus sp. for selenite (SeO32−) and lead (Pb2+) contamination. • Carbon source selection (glucose, cooking oil, crude oil) significantly influenced removal rates. • Achieved rapid SeO32− and Pb2+ reduction rates with glucose and cooking oil, but slow rates with crude oil. • Biosurfactant production possible across all carbon sources. • Reduction mechanisms: bioprecipitation for SeO32− and biosorption for Pb2+ This study explored Enterococcus sp.'s potential for bioremediating selenite (SeO 3 2− ) and lead (Pb 2+ ) contamination using different carbon sources (glucose, cooking oil and crude oil) while elucidating the underlying mechanisms. Aerobic batch reduction experiments were conducted (35±2°C, 120 rpm, pH≈8, 50 h) with an initial 1 mM concentration of either SeO 3 2− or Pb 2+ which was quantified by Ion Chromatography and Atomic Absorption Spectroscopy respectively. Key results showed that carbon source selection significantly influenced SeO 3 2− and Pb 2+ removal rates, elemental selenium (Se 0 ) formation, and protein synthesis. Glucose and cooking oil were found to be the most efficient, leading to rapid SeO 3 2− reduction (58 % and 55 % reduction, respectively), compared to crude oil (39 %). Similarly, Pb 2+ removal rates followed a similar trend, with 38 %, 33 %, and 25 % reduction using glucose, cooking oil, and crude oil, respectively. The study also highlighted Enterococcus sp.'s varied mechanisms for SeO 3 2− and Pb 2+ reduction, with SeO 3 2− precipitating to Se 0 while no precipitation of Pb 2+ to Pb 0 was observed. Furthermore, the bacteria exhibited versatility in biosurfactant production across the various carbon substrates. The biosurfactants notably promoted Se 0 precipitation thus shedding light on their potential role in metal ion bioreduction.