RESUMO
Bioremediation of chromium (Cr(â ¥)) contaminations has been widely reported, but the research on its removal mechanism is still scarce. Studies on Cr(â ¥) removal by strains affiliated to genus Pseudochobactrum revealed the Cr(â ¥) efficiency removal through the reduction of Cr(â ¥) to Cr(â ¢). However, the location of Cr(â ¥) reduction reaction and exact mechanism are still unspecified. In this work, a Gram-positive bacterial strain, Pseudochrobactrum saccharolyticum W1 (P. saccharolyticum W1) was isolated and tested to remove approximately 53.7% of Cr(â ¥) (initial concentration was 200â¯mgâ¯L-1) from the MSM medium. Analysis of SEM-EDS and TEM-EDS indicated that chromium-containing particles precipitated both on the cell surface and in the cytoplasm. Batch experiments indicated that the heat-treated bacterial cells almost had no ability to remove Cr(â ¥) from solution, while the resting cells could remove 62.0% of Cr(â ¥) at the initial concentration of 10â¯mgâ¯L-1. Additionally, at this concentration, 64.8% and 70.8% of Cr(â ¥) was reduced by cell envelope components and intracellular soluble substances after 6â¯h, respectively. These results suggested that the removal of Cr(â ¥) by P. saccharolyticum W1 was through direct reduction, which occurred on both cell envelop and cytoplasm. The results also showed that cytoplasm was the main site for Cr(â ¥) reduction compared to the cell envelop. Further analysis of FTIR and XPS verified that C-H, C-C, CO, C-OH and C-O-C groups of cells involved in correlation with chromium during Cr(â ¥) reduction. The study offered an insight into the Cr(VI) reduction mechanism of P. saccharolyticum W1.