Simultaneous transformation of tetracycline and nitrogen (ammonium/nitrite) by Sphingobacterium kyonggiense T8:...

Nitrogen pollution often coexists with tetracycline (TC) residues, resulting in complex co-pollution scenarios. However, the potential and mechanisms underlying the simultaneous removal of tetracycline and nitrogen by microbiological processes in the environment remain poorly understood. This work isolated a strain Sphingobacterium kyonggiense T8 capable of TC degradation and ammonia/nitrite transformation. It was found that the culture conditions affect the degradation efficiency of TC by controlling the bacterial biomass, while carbon sources regulated it by adjusting the catalytic efficiency per unit cell. When TC and ammonia nitrogen coexisted, TC was nearly completely removed, and 10 % of the ammonia nitrogen in the culture medium was assimilated into biomass nitrogen. In the coexistence system of TC and nitrite nitrogen, 21.6 % of nitrite nitrogen was converted into gaseous nitrogen, and TC was also nearly removed. Fifteen possible transformation products were captured, and a plausible transformation pathway of TC was proposed, involving hydroxylation, demethylation, decarbonylation, dehydration, dehydrogenation, and isomerization. The synchronous removal mechanism of TC and nitrogen was proposed by integrating genomic analysis and synchronous removal characteristics. Among the two TetX genes (86 aa and 386 aa), only the longer one (386 aa) encode a flavin-dependent monooxygenase with a complete function domain, which was involved in the biotransformation of tetracycline. Ammonia nitrogen and nitrite were removed via assimilation and heterotrophic aerobic denitrification by strain T8, respectively. These findings clarify the environmental fate of antibiotics and nitrogen, and strain T8 may develop into a potential remediation technology of antibiotic-nitrogen co-polluted water and soil.