isolation and identification of obligately chemolithoautotrophic, haloalkaliphilic bacterium thioalkalivibrio sp. strain ema and optimizing its thiosulfate removal activity in haloalkaliphilic condition

Introduction: Dischargeing hazardous pollutants of oil and gas industries such as spent caustic into the soil and water is an environmental concern for which biological treatment could offer a solution. To remove high levels of sulfur compounds in spent caustic waste, isolation of chemolithoautotrophic sulfur-oxidizing bacteria from Meighan wetland was considered in this study. Materials and methods: For isolation of chemolithoautotroph haloalkaliphile sulfur-oxidizing bacteria, alkaline sulfur-respiring medium with sodium thiosulfate as the sole electron and energy source and sodium carbonate/bicarbonate as carbon source were utilized. To confirm that the purified isolates are obligated autotroph, their growth on nutrient agar medium was surveyed and selected strains were identified based on 16S rRNA sequence analysis. The growth and activity of selected strain named EMA were optimized at various pHs and salt conditions by assessment of protein content and remained thiosulfate in the culture medium. Results: Following enrichment, 10 chemolithoautotrophic, haloalkaliphilic sulfur-oxidizing strains were isolated. 16S rRNA sequence analysis, showed that the strains belonged to the genus Thioalkalivibrio. The optimal growth and thiosulfate removal of the selected strain were obtained at pH 10 and 50 g/l of salt (sodium chloride or sodium sulfate). At higher salt concentrations, thiosulfate removal was higher in the presence of sodium sulfate, rather than sodium chloride. Discussion and conclusion: high sulfur removal activity of the isolated haloalkaliphilic Thioalkalivibrio strains in extreme conditions with these bacteria could be promising for the biotreatment of spent caustic.