Uranium sequestration by biofilm-forming bacteria isolated from marine sediment collected from Southern coastal region of India

Abstract

The present study was aimed at isolation of unique bacteria with radio-tolerance capability, biofilm formation as well as having an ability to sequester uranium. Marine sediment bacteria were isolated and were molecularly characterized. Among the 13 isolates (denoted as MS-1 to MS-13), 9 isolates showed good biofilm-forming ability. The bacterial isolates MS-8 and MS-13 were found to be radio-tolerant, they could survive up to 1000 Gy of radiation dose. Three bacterial strains namely MS-8, MS-11 and MS-13 showed both efficient biofilm formation and uranium sorption ability. These isolates were identified as Exiguobacterium profundum (MS-8), Pseudomonas putida (MS-11), and Bacillus marisflavi (MS-13). Removal of uranium from aqueous solution was studied in batch mode using these bacterial biofilms. The maximum biosorption capability of uranium on MS-8, MS-11 and MS-13 were 45%, 65% and 55% respectively with an initial uranium concentration of 100 mg/L. MS-11 biofilm showed highest U uptake when compared to that of other biofilm-forming strains. In MS-11, U sequestration was up to 88%, when treated with lower U concentrations (1 mg/L to 50 mg/L). The autoclaved biofilm biomasses were able to retain their U sorption capacity proving that the U bioremediation process is mainly a biosorption phenomenon. Further experiments showed ambient temperature and pH range of 3.0–5.0 are optimum physicochemical parameters for maximum uranium removal efficiency by E. profundum MS-8, P. putida MS-11, and B. marisflavi MS-13. FTIR results further confirmed the adsorption of uranium by amino, hydroxyl and amide groups. Among the 13 isolates, overall, P. putida MS-11 showed good biofilm formation and significant U removal at both higher and lower concentrations, with radiation dose tolerance up to 100 Gy. This study specifies the potential application of this bacterium for bioremediation.