Microbiological treatment of selenium containing materials

Abstract

Two selenite reducing bacteria Se1 and Se5 exhibited high capability to remediate selenite and production of elemental selenium were isolated from Ismailia canal in front of Abu Zaabal Fertilizers & Chemicals Company and Car maintenance facility, Co-operative gas station, Musturad, Egypt respectively. These 2 isolates were identified by 16S rRNA gene into Zobellella denitrificans Se1 and Pseudomonas stutzeri Se5. Thioredoxin reductase B (trxB) gene that belongs to selenite reduction pathway was successfully genotyped from both strains using newly designed primers. Phylogenetic analysis showed that trxB of Z. denitrificans Se1 was grouped with P. stutzeri Se5 and scored a single point missense mutation 89 G >T (A30L). Moreover, the results demonstrated that a horizontal gene transfer of trxB gene from P. stutzeri Se5 to Z. denitrificans Se1. Several growth conditions including different types and concentrations of electron donor, electron acceptor concentrations, incubation periods, pH, inoculum sizes and incubation temperatures were studied to achieve maximum reduction of selenite. The optimum conditions for maximum reduction were 100 mM lactate, 10 mM, 7 days, 7, 1 ml and 30°C respectively with maximum Se° production reached to 15.01 ± 0.31 and 20.53 ± 0.75 mg l-1 for Z. denitrificans Se1 and P. Abstract 1 stutzeri Se5 respectively. TEM analysis revealed the formation of nano size spherical selenium particles in the bacterial cells.