| Microbial dissimilatory Fe(III)reduction is ananaerobic respiration metabolic process of microorganisms.Dissimilatory Fe(?)reduction and Fe(?)-reducing bacteria can be found in any anaerobic environment of nature.Marine sediment is the main habitat of the dissimilatory Fe(?)-reducing bacteria because of its unique anaerobic environment.Therefore,FeI?)-reducing bacteria were enriched from the bohai sea sediment.Characteristics of dissimilatory Fe(?)reduction by Fe(?)-reducing bacteria were analyzed.The effect of dissimilatory Fe(?)reduction on morphology of Cr(VI)and biological hydrogen-producing were investigated.The main research results are following:(1)Marine sediments collected from Bohai of Tianjin were anaerobically enriched to obtain dissimilatory Fe(?)-reducing bacteria.Characteristics of dissimilatory Fe(III)reduction by Fe(?)-reducing bacteria were investigated under different electron acceptors.After fermentation for 12 h,the Fe(?)concentration of culture was 100.67 ± 0.75 mg·L-1 and 53.24 ± 3.63 mg·L-1 respectively,using ferric citrate and ferric hydroxide as electron acceptors.After 60 h,the Fe(?)concentration of culture was 118.95 ± 1.47 mg·L-1 and 119.74±3.96 mg·L-1 respectively.The results indicated that soluble and insoluble electron acceptors could significantly affect Fe(?)reduction processes,but had no significant effect on the accumulation of Fe(?).(2)Diversity of mixed culture and composition of dominant bacteria under different electron acceptors were analyzed by high throughput sequencing.Shannon diversity index of the bacterial community was 3.40 and 3.11 using ferric citrate and ferric hydroxide as electron acceptor,respectively,being higher than that of control group(with Shannon index 2.07).Such a result indicated that cultivation system with Fe(?)addition could significantly enhance the diversity of mixed culture.Analysis of microflora structure showed that the dominant populations in the Fe(?)-reducing bacteria were Clostridium and Romboutsia,belonging to Clostridiales,which indicated that Clostridiales were the dominant bacteria in the mixed culture under Fe(?)-reducing conditions.(3)A Fe(?)-reducing bacterium,Enterococcus sp.ZQ21(GenBank MF192756),was isolated using three layer plate method from the marine sediment in Bohai and identified by 16S rRNA gene sequence analysis.Characteristics of Fe(?)reduction by strain ZQ21 was investigated under different conditions.The results showed that strain ZQ21 had high Fe(?)-reducing activity using pyruvate with Fe(? concentration of 113.14 ± 3.46 mg·L-1,among different electron donors of EDTA,citrate,glucose,acetate,pyruvate and formate,under ferric citrate as electron acceptors.And strain ZQ21 had high Fe(III)-reducing activity using glucose with Fe(?)concentration of 91.38 ±2.41 mg·L-1,under iron hydroxide as electron acceptors.The Fe(?)-reducing activity by strain ZQ21 was improved by the addition of anthraquinone-2-sulfonic acid sodium(AQS)when iron hydroxide was as electron acceptors,which increased Fe(?)concentration by 47%compared with that of the control group.(4)The effects of dissimilatory Fe(?)reduction by strains ZQ21 on morphology of Cr(VI)were investigated.Different Cr(?)concentrations were set,such as 0,5,10,15,20,25,30mg·L-1.The results showed that the strains ZQ21 could grow well at low Cr(?)concentration(0?10 mg·L-1).Under Cr(VI)concentration 10 mg·L-1,strains ZQ21 A600 was 0.16 ± 0.004,and Cr(?)reduction rate was 18%.Different Fe(?)concentrations were set,such as 0,200,400,600,800,1000mg·L-1.The cell growth by strains ZQ21and Cr(?)-reducing activity were improved when Fe(?)was added to the culture.With Fe(?)concentration 800 mg·L-1,strains ZQ21 had the highest Cr(VI)reduction rate of 83%,which increased Cr(?)reduction rate by 4 times compared with that of the control group.(5)Characteristics of dissimilatory Fe(?)-reduction by strain ZQ21 was different using ferric citrate and iron hydroxide as electron acceptors with Fe(?)concentration of 119.80 ± 0.77 mg-L-1 and 30.61 ± 0.89 mg-L-1 respectively.The corresponding hydrogen production of 1395.30 ± 4.79 mL·L-1 and 174.30 ± 3.23 mL·L-1 respectively,which were 60 times and 8 times compared with that of the control group.The metabolic pathways of hydrogen-producing by strain ZQ21were different using ferric citrate and iron hydroxide as electron acceptors with ethanol fermentation,butyric fermentation respectively.Dissimilatory Fe(III)reduction by strain ZQ21 was coupling with hydrogen production. |
PDF Full Text Request