Abstract:

Inorganic sulfur（S^2-）was used as the target pollutant,and an indigenous microorganism capable of efficient S^2--oxidizing was isolated from Dongsha river,a black-odor water body in Beijing. Through 16S rRNA sequencing experiment,this strain was identified as Citrobacter and named as Citrobacter sp.sp1. The optimal S ^2--oxidizing conditions of this strain sp1 were as follows：25℃,initial pH of 7.0,and initial glucose concentration of 1.00 g/L along with initial cell concentration of 1.00 g/L. Under the above optimal conditions,the highest S^2--oxidizing ratio of artificial sulfur-containing wastewater by this strain sp1 reached 97.1%. Five chemical forms of sulfur including S⁰、S₂O₃^2-、SO₃^2-、S₄O₆^2- and SO₄^2- were produced in the whole bio-reaction process,and the concentration of SO₄^2- increased slowly with the decreasing of S^2-. Results of high-throughput sequencing showed that the strain sp1. transformed the unsteady-state S^2-into steady-state SO₄^2-via two main S^2--oxidizing metabolic pathways of Paracoccus sulfur oxidation（PSO）and S4 intermediate（S4I）. In PSO pathway,S^2- partially was oxidized to be S⁰ and then the generated S⁰ continuously was oxidized to be SO₃²,while other part of S^2- were directly bio-converted to SO₃²,and intermediate SO₃^2- were further oxidized to SO₄^2- by both directly and indirectly oxidation pathways;in addition,S⁰ reacted with SO₃^2- spontaneously to form S₂O₃^2-,while S₂O₃^2- released SO₃^2- and S⁰ by the disproportionate reaction. In S4I pathway,S₂O₃^2- partially was oxidized to S₄O₆^2-,and S₄O₆^2- subsequently was then oxidized to SO₄^2-.

Key words: black-odor water body, S^2-, sulfur-oxidizing bacterium, sulfur-oxidizing characteristics, metabolic pathway