Enrichment And Mechanism Of An Aerobic Bacterial Consortium For Autotrophic Biodegradation Of Thiocyanate

Thiocyanate is widely used in a variety industrial producing,it will generate many environmental problems if the effluent containing thiocyanate was poorly treated.Microbial bioremediation is the most reliable and efficient approach for environmental pollution problem and ecological crisis currently,except the high efficiency,bioremediation won't produce other pollution.Thiocyanate was degraded into sulfate,carbon dioxide and ammonium by microbial organism which can utilize thiocyanate as energy source.In this paper,we got the aerobic autotrophic microbial consortium.By high throughput sequence,it was clear that the proportion of Thiobacillus had an distinct increase,from 0.67%of environmental sample increased to 43.3%of enrichment.Except Thiobacillus,the enrichment consortium also contain Terrimonas?9.2%?,Pseudomonas?5.9%?,Thermomonas?5.7%?,uncultured Betaproteobacteria?19.4%??The consortium can tolerate thiocyanate with concentration of 70 m M.In a continuously bioflim reactor,HRT was progressively decreased from48h to 10 h and the vvm(air volume·culture volume^-1·min^-1)was simultaneously increased from 0.125to 0.375 during the operation period.In the biofilm bioreactor,the loading concentration of SCN^-was increased from 3.5 mmol L^-1 to 34.5 mmol L^-1 across 160days inoculation,the consortium can degrade thiocyanate with the maximum rate of1.4 mmol L^-1 h^-1.Within the genomes,the SQR is widely distributed in all bins except for the uncultured Chitinophagaceae SCNH1,which suggests the oxidation of H₂S to S⁰was prevalent in the bacterial consortium.The presence of fcc B in the genomes of Hydrogenophaga SCNH2,Pelomonas SCNH6,Thiobacillus SCN1 and Thiobacillus SCN2 also demonstrated their ability to oxidize sulfide.Besides the SQR and Fcc B,the Sox enzyme complex and Dsr AB are also able to perform sulfide oxidation,which generates SO₄^2-and SO₃^2-as final products,respectively.The Sox complex was found in the genomes of Hydrogenophaga SCNH2,Pelomonas SCNH6,Thiobacillus SCN1and Thiobacillus SCN2,however,the Sox system in both Thiobacillus bins are incomplete because they lacking a Sox CD complex.Due to the lack of Sox CD,the intermediate could not be further oxidized into SO₄^2-via the sox pathway and then would be plausibly fed into other sulfur oxidation pathways or into storage forms of sulfur.As a consequence,the sulfide was completely oxidized into SO₄^2-by the Hydrogenophaga and Pelomonas groups while into sulfur granules by the Thiobacillus group.Because the Dsr AB and Sdo encoding genes were also detected in the genome?s?of Thiobacillus,the sulfide if diffusing into cytoplasm would be oxidized into SO₃^2-by the Dsr AB and the stored sulfur would also be further oxidized into SO₃^2-by the periplasmic Sdo.Moreover,the genes encoding Apr AB were identified in the genomes of Thiobacillus SCN1 and Thiobacillus SCN2,and enzyme Soe ABC in the genomes of Hydrogenophaga SCNH2,Dokdonella SCNH5,Thiobacillus SCN1 and Thiobacillus SCN2.Apr AB and Soe ABC are two kinds of membrane-bound enzymes and were reported to catalyze the oxidation of SO₃^2-to SO₄^2-in the cytoplasm.Then,the Thiobacillus group was able to oxidize the SO₃^2-that produced through the Dsr AB catalysis or transported from periplasm into cytoplasm.According to the genome-based analysis,a cross-feeding pattern between the SCN^--degrading autotrophs?produce sulfide and organics?and sulfide-oxidizing heterotrophs?completely oxidized sulfide into sulfate?was proposed,which then helped to make the SCN^--removal a net free energy-yielding process,contributing to the high removal efficiency.