Study On Metabolism Pathway Of Nitrogen Removel By A New Strain

A new strain with the ability of heterotrophic nitrogen removal was isolated during the study of membrane bioreactor process preliminarily. Through 16s rRNA gene sequencing analysis, the bacteria was related to Providencia rettgeri and there after named Providencia rettgeri strain YL. Providencia rettgeri strain YL can utilize organic carbon or organic nitrogen as carbon and nitrogen source.In aerobic conditions, Providencia rettgeri strain YL not only completed the process of nitrification but also produced nitrogen. Some special bacteria have the ability of heterotrophic nitrification and aerobic denitrification, there by allowing nitrification and denitrification to accur at the same time in a reactor, which is different from traditional biological nitrogen. Heterotrophic nitrification bacteria in nitrogen removal significantly valued in wastewater treatment. In our country, the study on the phenomenon of heterotrophic nitrification and heterotrophic nitrification mechanism is still in its early stages. In order to apply heterotrophic nitrification to the use of engineering practice, we should further study on the heterotrophic nitrification phenomenon and mechanism of heterotrophic nitrification. With the support of the National Natural Science Foundation Project (No.20676078), this paper inspected growing conditions of Providencia rettgeri strain YL and investigation regarding its metabolism pathway of nitrogen removal. The main results were as follows:Varying carbon and nitrogen sources, temperature, pH, shaking speeds and microelements were investigated to identify the optimal conditions for nitrogen removal. The results were as follows: temperature 30℃, pH 7.0, shaking speed 120r/min, the presence of magnesium ions. Glucose and ammonium chloride were the best carbon and nitrogen sources.The NH2OH, NO2--N and NO3--N were the intermediate products during the ammonium metabolized by Providencia rettgeri strain YL.When NO2--N was added in the metabolism process of ammonium, the concentration of NO2--N was decreased. However, NO3--N did not accumulate.When NO3--N was added in the metabolism process of ammonium, the concentration of NO3--N was decreased, and NO2--N accumulated. Providencia rettgeri strain YL can metabolize and transform NO2--N and NO3--N.In order to obtain the key enzyme involved in the nitrogen removal process of Providencia rettgeri strain YL effectively and conveniently, the ultrasonic cell-disruption technique was used. Optimum conditions were chosen based on single-factor and orthogonal experimental results. The results showed that optimum conditions for cell-breakage of Providencia rettgeri strain YL via ultrasonication were: cell OD600 1.996, work times 70, work/interval time 5s/5s and ultrasonic output power 400W.The concentration of NH2OH was decreased in the HAO activity reaction test, which suggested the HAO existed. NO2--N, NO3--N were the product in the HAO activity reaction. In the NAR activity reaction test, the concentration of NO3--N was decreased.According to the research results and Richardson's nitrogen removal pathway, the possible nitrogen removal pathway of Providencia rettgeri strain YL was that NH4+-N was first transformed to NH2OH,then transformed to NO2--N, and finally transformed to N2, and there exists mutual transformation of NO2--N and NO3--N.