Study On The Characteristics Of Dissimilatory Nitrate Reduction To Ammonium By Shewanella Sp. RQs-106

Dissimilatory nitrate reduction to ammonium?DNRA?is another nitrate reduction method which is different from denitrification.It plays an important role in the nitrogen cycle in nature.DNRA can convert nitrate,nitrite or complexed NO into ammonium,which can be used by microorganisms as a nitrogen source in water,maintain the effect of nitrogen fertilizer in soil and recover nitrogen resources in waste gas purification.Due to the numerous factors affecting the DNRA process,it is necessary to explore the mechanism and influencing factors of the DNRA process of the pure strain.At present,there are few studies on DNRA progress under pure culture condition.Aiming at this problem,this experiment investigated the function of DNRA and its influencing factors of Shewanella sp.RQs-106 screened in this lab.The main contents are as follows.The ability of Shewanella sp.RQs-106 to reduce NaNO₂ at different C/N ratios was investigated.The results showed that the strain could effectively reduce 5 mM NaNO₂ to ammonium with good DNRA performance,and the appropriate C/N ratio was 20.The effects of different electron donors,electron acceptors,pH and temperature on DNRA progress were investigated.The results showed that the suitable electron donor was sodium lactate.Nitrite and complexed NO could be used as substrates for DNRA,but complexed NO was highly toxic,so nitrite was a suitable electron acceptor for stain RQs-106 in DNRA.The suitable pH value for the DNRA process was 7.2 and the temperature was 30°C.The effects of ammonia nitrogen concentration and nitrite concentration on DNRA progess were investigated.The initial addition of 5-20 mM NH₄Cl promoted the degradation of 5 mM NO₂^-by the strain,but the promotion effect was not obvious.Among them,the DNRA rate was the fastest in the 5 mM NH₄Cl group.10-20 mM NO₂^-inhibited the DNRA process of the strain.Under the condition of adding fixed biomass in the experiment,the appropriate initial nitrite concentration was 5mM.The strengthening mechanism of yeast extract,redox mediators and sulfide on DNRA was investigated.The results showed that yeast extract could slow down the inhibition of high concentration nitrite and promote the DNRA process with 5 mM NO₂^-as electron acceptor.Isotopic experiments showed that most of the ammonia nitrogen produced by the system after the addition of yeast extract came from the conversion of nitrite.The initial addition of nitrite was nearly 100%converted into ammonia nitrogen.The redox mediators?AQS,AQDS and Riboflavin?could significantly promote the DNRA process,and 20-150?M AQS could double the DNRA process of strain RQs-106.There was no significant difference in the promoting effect of AQS within the concentration range on the DNRA process.The appropriate adding amount of AQS for reducing 5mM nitrite was 20?M.The DNRA process of strain RQs-106was inhibited by adding 3.3 mM and 7.3 mM sulfide to the heterotrophic DNRA system,respectively.The strain RQs-106 not only has the function of heterotrophic DNRA,but also has the function of sulfur-autotrophic DNRA.Competition exists between the sulfur-autotrophic DNRA process and the heterotrophic DNRA process.