Study On The Role Of Microbial Metabolite Substances On Goethite And Methanogenic Archaea Coexistence System

In the process of biological wastewater treatment,microbial metabolite substances play an important role in the formation of microbial aggregates and transformation of pollutants.In recent years,the enhancement of anaerobic methanogenesis by iron oxide has been widely concerned by scholars at home and abroad.However,there are few reports about the role of microbial metabolite substances in this process.This study builds the goethite-methanogenesis system,using dialysis bags to concentrate microbial metabolite substances and investigate the changes of methane production efficiency and microbial community.Taking Shewanella oneidensis MR-1 as an example,the characteristics of microbial metabolite substances in different iron reduction system were investigated.The methanogens-iron reducing bacteria-goethite system was constructed,microbial metabolite substances of goethite-methanogenesis system were analyzed by iTRAQ proteomics and microbial community are characterized by high-throughput sequencing.The main conclusions are as follows:1)The use of dialysis bags was beneficial to improve the contact possibility between goethite and microorganisms,but the dialysis with larger molecular weight(10kDa)had little effect on methane production rate.However,the use of dialysis with smaller molecular weight(2000Da)significantly increased the concentration of SMP and methanogenesis rate.It was also found that SMP especially flavins secreted from microorganisms could play an important role in the goethite facilitated methane production process.Additionally,enrichment of SMP not only improved the abundance of electroactive bacteria and but also promoted the growth of aceticlastic methanogens Uncultured Methanosaeta sp..2)The effects of different conductive materials on iron reduction and microbial metabolite substances especially flavins of S.oneidensis MR-1 were studied to explore the possible iron reduction behavior in methane system.It was found that the influences of the conductive material on the reduction of goethite by S.oneidensis MR-1 were mainly composed of two factors: the electron transfer efficiency and the cell activity.Goethite stimulated S.oneidensis MR-1 secrete more microbial metabolite substances in the early stages of culture,while the addition of conductive material reduced the ratio of flavins in SMP.CNTs effectively promoted the reduction of Fe-NTA,and the graphite had a positive effect on the reduction of goethite.3)The high-throughput sequencing results indicated that goethite could regulate the function of microbial community.The extracellular proteomics and microbial community analysis showed that goethite significantly promoted the terminal methanogenesis and extracellular electron transfer / redox-related processes.Firmicutes Anaerolinaceae and Synergistetes microbes were involved in the goethite-facilitated methane production process.At the same time,the addition of goethite made hydrogen-producing methane process possible in the rectors using acetate as the sole carbon source.iTRAQ results also indicated SMP proteins were mostly derived from the decline of cell integrity.