| Dissimilatory iron-reducing bacteria-mediated Fe(Ⅲ)is an important process in the biogeochemical cycle.The dissimilated iron reduction process can not only remove heavy metal pollution and degrade organic matter,but also can couple hydrogen production.The experimental strain in this paper is the dissimilated iron reducing bacteria Clostridium sp.LQ25 isolated from the sediments of the Bohai Sea.To study the effects of electron donors,electron acceptors and electron shuttles on the reduction and hydrogen production properties of strains of dissimilated iron,ombined with transcriptome data,the molecular mechanism of reducing hydrogen production by strain LQ25 dissimilated iron was analyzed.The experimental research results have the following aspects:Under different electron donors,the reached and hydrogen production properties of strain LQ25 dissimilated iron show that the strain could grow with sucrose,glucose,sodium pyruvate and sodium lactate as electron donors.When ferric citrated was used as the electron acceptor,strain LQ25 had the highest efficiency of reducing Fe(Ⅲ)by glucose dissimilation,and the concentration of Fe(Ⅱ)reaches 8.87±0.1 mg/L.When the strain used iron hydroxide as the electron acceptor,the reduction of Fe(Ⅲ)by sodium pyruvate is the most efficient,and the concentration of Fe(Ⅱ)reaches 8.27±0.2 mg/L.The strain produced the highest hydrogen production when using sucrose as the electron donor.When ferric citrate and ferric hydroxide were used as the electron acceptors,the hydrogen production was 653.4±7.5 ml/L and 475.2±4.4 ml/L,respectively.The sodium anthraquinone-2,6-sulfonate(AQDS)and riboflavin were set as electron shuttle bodies.When the concentration of AQDS was 0.5 mmol/L,the strain LQ25 dissimilated reduction Fe(Ⅲ)efficiency and hydrogen production were the highest,the concentration of Fe(Ⅱ)could reached 12.95±0.1 mg/L,the cumulative Fe(Ⅱ)concentration increased by 91.6%compared with the control group;the hydrogen production reached 673±3.6 ml/L,increased by 91.7%compared with the control group.When the riboflavin concentration was 100 mg/L,the strain LQ25 had the highest dissimilation reduction Fe(Ⅲ)efficiency and hydrogen production,and the Fe(Ⅱ)concentration reached 11.06±0.05 mg/L.The group increased by 63.6%,the hydrogen production reached 560±2.7 ml/L,which was increased by 60.7%compared with the control group.When ferric citrate and ferric hydroxide were used as electron acceptors,respectively,the strain LQ25 produced Fe(Ⅱ)concentrations of 9.03±0.2 mg/L and 5.12±0.03 mg/L,and iron reductase activity was 1.34 μmol/mg·h and 0.692 μmol/mg·h.Compared with insoluble iron,the efficiency of strain LQ25 using soluble iron for dissimilated Fe(Ⅲ)reduction was significantly improved,and Fe(Ⅱ)concentration and iron reductase activity increased by 76.7%and 93.6%,respectively.When ferric citrate is the electron acceptor,the cumulative hydrogen production of strain LQ25 was 534±2.7 ml/L,an increase of 160.5%compared with the control group,when ferric hydroxide is the electron acceptor,the cumulative hydrogen production of strain LQ25 was 253±4.7 ml/L,an increase of 23.4%compared with the control group.Under the three culture conditions of control group(without iron addition),ferric citrate and ferric hydroxide,strain LQ25 was collected and the transcriptome data was measured,and recorded as S1,S2 and S3 respectively.The results showed that compared with S2 strains,S1 strains had 18 significantly up-regulated genes and 18 down-regulated genes.Compared with S3 strains,S1 strains had 15 differentially expressed genes up-regulated and 9 down-regulated genes.Compared with the S3 strain,the S2 strain had 18 significantly up-regulated genes and 13 down-regulated genes.The protein functions annotated by the differential iron reduction ability genes are riboflavin and extracellular solute binding proteins.The proteins annotated with hydrogen-generating differential genes are Fe-4S binding protein,FMN binding protein,and FAD dehydrogenase:protein FMN transferase. |
