The effect of the antibiotic tetracycline hydrochloride on the biotransformation of urea when exposed to soil nitrifying strains

Introduction. The consequences of uncontrolled use of antibiotics in agriculture are an urgent problem of environmental hygiene. Tetracycline can enter the soil with the urine of domestic animals, inhibit the vital activity of soil bacterial strains and inhibit the processes of enzymatic hydrolysis of urea (carbamide), disrupting the global nitrogen cycle in nature. The lack of both quantitative and qualitative criteria for assessing this influence determined the relevance of the research.

Materials and methods. The studies were carried out using the “Stayer” chromatographic system with cationic and anionic separating columns and exclusive analysis methods developed by the authors. When modelling solutions of heavy metals, an atomic absorption spectrometer МГА-915МД with ЭTA was used. The objects of research were model solutions of carbamide with different content of inhibiting substances. As a source of urease and strains of Nitrobacter and Nitrosomonas, sod-podzolic soil from the Educational and Experimental Soil-Ecological Center “Chashnikovo” of Lomonosov Moscow State University was used.

Results. An improved, more rapid chromatographic method for the analysis of urea in water is proposed compared to the method described by the authors earlier. The inhibitory effect of the antibiotic tetracycline hydrochloride on the process of biotransformation of nitrite into nitrate caused by Nitrobacter strains has been shown. No significant effect of the antibiotic on the biotransformation of urea into ammonium and ammonium into nitrite under the action of Nitrosomonas strains has been established.

Limitations. The studies were carried out on the model of water systems, which included an aqueous phase containing different concentrations of the antibiotic, soil suspension, urea, heavy metal ions at a temperature of t = 30 °C, pH ~ 6.5. The influence of salt background, pH, and temperature on biotransformation has not been studied, which could, without changing the overall picture, reveal nuances in the kinetics of the main processes.

Conclusion. Studies have shown the absence of the effect of the antibiotic tetracycline hydrochloride on the kinetics of the decomposition of urea to ammonium and carbon dioxide due to urease enzymatic activity; there is no effect of the antibiotic on the oxidation of ammonium to nitrites by Nitrosomonas strains. It was found: selective inhibitory effect of an antibiotic during the oxidation of nitrite to nitrate, due to Nitrobacter strains; inhibition of biotransformation processes by chromium ions along the entire chain of transformations from urea to nitrate; and the inhibitory effect of excess oxygen on the totality of biotransformation processes during air bubbling through the aqueous phase.

Contribution:
Abramov E.G. — collection and processing of material, statistical processing, writing text, research concept, editing.
Antropova N.S. — collecting and processing material, writing text.
All authors are responsible for the integrity of all parts of the manuscript and approval of the manuscript final version.

Gratitude. The authors express their gratitude to A.V. Zagainova and the staff of the Microbiology laboratory of the FSBI "CSP" of the FMBA of Russia for their assistance in conducting experiments.

Conflict of interest. The authors declare no conflict of interest.

Acknowledgement. The study had no sponsorship.

Received: March 16, 2022 / Accepted: April 12, 2022 / Published: May 31, 2022