NH4^＋对合成气乙醇发酵过程的影响及其酶学机理

Effect of NH_4^+ on fermentation process of syngas for ethanol and research of enzymatic mechanism

为研究合成气厌氧乙醇发酵中合成气杂质组分NH_3对发酵过程的影响,实验通过考察发酵培养基内不同初始浓度的NH^+_4对菌株A-fm4,Clostridium ljungdahlii和Clostridium autoethanogenum DSM10061利用生物质合成气发酵乙醇的影响,证实低浓度的NH^+_4可促进菌体生长和乙醇发酵,当其浓度高于9.35 mmol/L时,菌体生长和乙醇发酵随其浓度的增大而抑制显著。对菌株在菌体生长期和乙醇/乙酸发酵期内4种关键酶的活性研究表明,氢化酶(H_2ase)、一氧化碳脱氢酶(CODH)、乙醇脱氢酶(ADH)和乙酸激酶(ACK)均受高浓度(149.6 mmol/L)NH^+_4抑制,且菌体生长期的酶活水平均高于发酵期的值。这说明在低浓度NH^+_4下可促进还原力的产出而利于乙醇发酵,而较高浓度NH^+_4抑制代谢途径,致使菌体生长和乙醇发酵受阻。菌株C.ljungdahlii和C.autoethanogenum DSM10061的K_i值分别为208.13 mmol/L和240.37 mmol/L,耐铵能力较强,可作为未来耐铵菌株的驯化提供材料,为降低工业生产成本和减少合成气净化工艺工序奠定基础。

To investigate the effect of impurity NH_3 on anaerobic fermentation process of syngas for ethanol,the batch fermentation at different initial concentrations of NH4^＋using microbial strains A-fm4,Clostridium ljungdahlii and Clostridium. autoethanogenum DSM10061 was conducted. The results show that lower concentration of NH_4~＋stimulates cell growth and acetate fermentation,while the concentration of higher than 9. 35 mmol / L significantly inhibits the cell growth and ethanol fermentation. Based on the research of enzymatic mechanism during growth period and ethanol or acetate period,it proves that the key enzymes（ H_2 ase,CODH,ADH and ACK） existed in metabolic pathway are all inhibited by higher concentration of NH4^＋（ 149. 6 mmol/L）,and the levels of enzyme activity of growth period are higher than the levels of enzyme activity of fermentation period. These show that lower concentration of NH_4~＋will improve the utilization efficiency of carbon source by stimulating reducing power production as well as benefit for ethanol production,the higher concentration of NH4^＋will inhibit cell growth and ethanol fermentation process and then the metabolic pathway is restrained. Moreover,the research also shows that the K_ilevel of C. ljungdahlii and C. autoethanogenum DSM10061 is 208. 13 mmol / L and 240. 37 mmol / L respectively,both of them have a stronger ability of resistance to NH4^＋,this will provide microorganism resources for domestication of resistance to NH4^＋,also lay the foundation for reducing industrial production costs and simplifying the gas purification procedure in syngas fermentation.