Aerobic reduction of selenite and tellurite to elemental selenium and tellurium nanostructures by Alteromonas sp. under saline conditions

Abstract

Selenium (Se) and tellurium (Te) wastewaters are typically characterized with higher salinities. Limited studies have determined microbial reduction of Se/Te oxyanions under saline conditions. This study reports bacterial reduction of Se(IV)/Te(IV) oxyanions at different salinities by a bacterial strain isolated from selenite-reducing halophilic aerobic granular sludge. Among several isolates, ORB-2 was consistent and efficient in reducing selenite and tellurite under saline conditions. This strain showed higher tolerance and grew rapidly in the presence of 10 mM selenite (790 mg L−1 Se(IV)) and 7.5 mM tellurite (957 mg L−1 Te(IV)). Growth was accompanied by Se(IV)/Te(IV) removal and conversion to cell-associated red/black elemental forms. Selenite (0.25–2 mM; 20–158 mg L−1 Se(IV)) removal efficiencies ranged between 82 and 96% with maximum removal by 48 h. For tellurite (0.25–2 mM; 32–254 mg L−1 Te(IV)), the removal efficiencies were 75–92% in 72 h. Growth of ORB-2 and concomitant removal of selenite or tellurite was observed in the presence of 2–8% NaCl. Biogenesis of Se(0) and Te(0) nanostructures was confirmed by micro-Raman spectroscopy. Extracted Se(0) and Te(0) nanostructures had a hydrodynamic diameter of 180 and 111 nm, respectively. Based on 16S rRNA gene sequencing, ORB-2 was identified as Alteromonas sp. Efficient conversion and association of biogenic Se(0)/Te(0) nanostructures with the cells under saline conditions shows promising use in bioremediation and scarce metal(loid) recovery.