The Effects Of DDT Contamination On Ammonia Oxidation And Of Ammonia-Oxidizing Microorganisms In Soil

Dichlorodiphenyltrichloroethane?DDT?,as one of Persistent Organic Pollutants?POPs?,is a long-period contaminant in soil until now.It seems to be one of nitrification inhibitors due to its chemical structure,but little reports have been published on that.Ammonia oxidation,as the first step in the nitrification process?NH₄⁺-N?NO₂^--N?NO₃^--N?,plays a central role in the global nitrogen cycling.The differential contributions of ammonia-oxidizing bacteria?AOB?and ammonia-oxidizing archaea?AOA?have been the controversial focus due to their responsibility for ammonia oxidation.At present,there are many studies on the ecological functions of AOA and AOB in the natural environment such as farmland,mountainous area and river bottom,but there are few reports on the ammonia oxidation process and related AOA and AOB studies in the polluted environment.As one of persistent organic pollutants?POPs?,DDT has a long history of environmental pollution,and there are many studies on environmental science,but there is no report on its influence on soil ammoxidation process and ecological mechanism.In this research,we try to study the mechanism of DDT contamination on the ammonia oxidation as well as AOA and AOB in soils.The abundance,function and community structures of AOA and AOB will be analyzed by quantitative real-time PCR and pyrosequencing of their specific genes amoA and 16S rRNA in DDT-contaminated soils.With microbial species diversity sequencing and functional gene sequencing,the active AOA and AOB abundance will be also quantified in order to confirm their relative contributions in ammonia oxidation during DDT contamination,and meanwhile their function and community structures may be investigated by quantitative real-time PCR and pyrosequencing,too.In a word,this program systematically demonstrate the mechanism of ammonia oxidation in DDT-contaminated soils and provide a theory and data basement for the control of DDT-contaminated soils and ammonia oxidation behavior in contaminated environment.Then we found that the NH₄⁺-N concentration increased obviously in DDT-contaminated soils compared to the uncontaminated samples,indicating ammonia oxidation may be inhibited.The main findings of this study are as follows:1.Soil ammonia oxidation is inhibited in the early stage of DDT pollution,and increases with the increase of DDT pollution concentration,but it can adapt and gradually recover after about 16 days.2.In the soil samples,the genus Sphingononas of family Sphingomonadaceae,the family Anaerolineaceae and the family Nitrosomonadaceae account for the largest proportion of soil flora.Among them,the genus Sphingononas significantly increased in the 6th to 10th days,becoming a dominant species,indicating that the genus Sphingononas is the most affected bacterial community when the ammonia oxidation process is inhibited,and it also dominates the degradation of DDT.The class Crenarchaeotic,the family Nitrososphaera,the order Thermoplasmatales,the genus Candidatus Nitrosotalea and other two genera of unclassified archaea account for the largest proportion of archaea in the soil.The family Nitrososphaera is the dominant archaea that dominates the digestive process and has strong adaptability to DDTThe high DDT concentration?20mg/kg dry soil?has a significant effect on the bacterial microbial community and low concentration of DDT has less effect on the bacterial community.The microbial community of archaea showed a significant gradient with the increase of DDT concentration,indicating that the archaeal community was more sensitive to the change of DDT content.3.The order Nitrosomonadales,the genus Ntrosospira and the family Nitrosomonadaceae account for a large proportion of AOB in the soil samples.The order Nitrosomonadales are the dominant ammoxidation bacteria community that dominates the ammoxidation process.The phylum Crenarchaeota,the genus Ntrososphaera and two types of unclassified ammonia-oxidizing archaea accounted for the largest proportion of AOA in soil samples.4.RDA analysis revealed the correlation between the horizontal community composition of bacteria and archaea in different soil samples and different environmental factors.Sphingomonas is the most obvious bacteria affected by chloride and ammonia nitrogen;Anaerolineaceae is the most obvious bacteria affected by nitrate nitrogen,DDT,DDE and DDD.The family Nitrososphaera is the archaea most affected by DDT and nitrate nitrogen.The phylum Crenarchaeota is the most obvious ammonia-oxidizing archaea affected by chloride and ammonia nitrogen.The family Nitrososphaera is the most obvious ammonia-oxidizing archaea affected by DDT and nitrate nitrogen.The abundance of Ntrososphaera is sensitive to DDT stimulation,and Crenarchaeota and Ntrososphaera are dominant ammoxidation archaeal communities.Nitrosomonadales are ammonia-oxidizing bacteria most affected by nitrate nitrogen and DDT.5.In the medium phase,ammonia oxidizing bacteria have good adaptability to DDT.In the late phase,ammonia-oxidizing archaea has good adaptability to DDT.Later AOA is the dorminant community of ammonia oxidation processes.Combined with the analysis of community composition,Ntrososphaera is the genus of ammonia-oxidizing archaea which is dominant in the ammoxidation process.The addition of methanol has a temporary stimulation to the soil archaea community.With the prolongation of time,the volatilization of methanol and the adaptation of microorganisms to methanol,methanol has no obvious inhibitory effect on soil archaea community.