Effects Of Three Small Molecular Organic Matters On The Compound Culture Of Nitrification Functional Microorganisms

The main pollutants in aquaculture waters are ammonia and nitrite,which are direct or indirect factors causing biological diseases in water bodies,and thus have become the focus of attention in aquaculture.Most of the nitrifying bacteria found so far are autotrophic nitrifying bacteria,which are divided into ammonia oxidizing bacteria?AOB?,ammonia oxidizing archaea?AOA?and nitrite oxidizing bacteria?NOB?,which are involved in the ammoxidation stage in nitrification and Nitrous acid oxidation stage.Sodium formate,sodium acetate,and sodium pyruvate are small molecular organic substances that can be decomposed and utilized by bacteria.Studies have shown that nitrifying bacteria contain enzymes that can oxidize these three organic substances,and nitrifying bacteria can use them for growth and metabolism.However,the activity of nitrifying bacteria is affected by many factors.When organic matter is present in the water,bacteria will compete for dissolved oxygen and living space.Nitrifying bacteria act as autotrophic bacteria,and their growth and reproduction ability is inferior to that of heterotrophic bacteria.Understanding the effects of organic carbon on the nitrification process and the relationship between nitrifying bacteria and heterotrophic bacteria are important for aquaculture system design and wastewater treatment system design.In this paper,the effects of three small molecular organic substances?sodium formate/sodium acetate/sodium pyruvate?on the ammoxidation activity and nitrite oxidation activity of nitrifying bacteria preparations were studied with self-prepared seawater/freshwater nitrifying bacteria preparations.The high-throughput sequencing method was used to analyze the bacterial community structure and diversity before and after the addition of organic matter in some experimental groups.Through the research,the following conclusions were obtained:?1?Sodium formate has an inhibitory effect on seawater-type ammoxidation activity and nitrite oxidation activity,and promotes freshwater nitrite-oxidizing bacteria,and has little effect on freshwater ammonia-oxidizing bacteria activity.Among them,the volumetric weight?w/v?of sodium formate was 0.25,which had the greatest inhibition effect on seawater-type ammonia oxidizing bacteria and nitrite oxidizing bacteria.When w/v was 0.10,the promotion effect on freshwater nitrite oxidizing bacteria was the largest.?2?The effects of sodium acetate on the two nitrifying bacteria preparations were different,and the effects on the activity of seawater ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were also different.The specific performance was that the addition of higher concentration of sodium acetate significantly inhibits the activity of seawater ammonia oxidizing bacteria?w/v was 0.15?0.25?,while the low concentration of sodium acetate promotes the activity of seawater type nitrite oxidizing bacteria?w/v was 0.05?.The inhibitory effected of sodium acetate on the activity of freshwater ammonia oxidizing bacteria increased with increasing concentration,but had little effect on freshwater nitrite oxidizing bacteria.?3?Low concentration of sodium pyruvate can promote the activity of ammonia oxidizing bacteria in the two nitrifying bacteria preparations but inhibit the activity of nitrite oxidizing bacteria,and the inhibition effected on fresh water nitrite oxidizing bacteria was stronger than that of sea water type.Respectively,the optimum volumetric weight of sodium pyruvate for the degradation of ammonia nitrogen by seawater/freshwater ammonia-oxidizing bacteria was 0.10 and 0.15.?4?Analysis of seawater NH₄⁺-N group?H2?,seawater NO₂^--N group?H3?,freshwater NH₄⁺-N group?D2?and freshwater NO₂^--N group after adding sodium pyruvate by high-throughput sequencing method?D3?and the community structure and diversity of bacteria in the initial microbial agents?H1,D1?of the two nitrifying bacteria were analyzed.It was found that the microbial richness in the seawater group and the freshwater group decreased after the addition of sodium pyruvate,and NH₄⁺-N treatment group was higher than the NO₂^--N treatment group.The dominant bacteria in the six samples were Proteobacteria and Bacteroides.The relative abundance of ?-Proteobacteria in the seawater experimental group was higher than that in the control group,and the relative abundance of Bacteroides was reduced.Nitratireductor and Nitrosococcus in H2 relative abundance of genus and nitrococcus is significantly improved compared with the control group,wherein the nitrosococcus can convert the ammonium salt into nitrite,and the nitrococcus can convert the nitrite into nitrate.In the freshwater experimental group,the relative abundance of ?-proteobacteria increased compared with the control group,and the relative abundance of ?-proteobacteria decreased.Among them,the relative abundance of Zobellella in the ?-proteobacteria increased,which is a kind of salt-tolerant heterotrophic Nitrification-aerobic denitrifying bacteria.At the same time,the relative abundance of the genus Paracoccus increased after the experiment,which has the ability to reduce nitrate to nitrite and then to N2.