The fate of doxycycline (DC), a second generation tetracycline antibiotic, in the environment has drawn increasing attention in recent years due to its wide usage. Little is known about the biodegradability of DC in the environment. The objective of this study was to characterize the biotransformation of DC by pure bacterial strains with respect to reaction kinetics under different environmental conditions and biotransformation products. Two bacterial strains, Brevundimonas naejangsanensis DD1 and Sphingobacterium mizutaii DD2, were isolated from chicken litter and characterized for their biotransformation capability of DC. Results show both strains rely on cometabolism to biotransform DC with tryptone as primary growth substrate. DD2 had higher biotransformation kinetics than DD1. The two strains prefer similar pHs (7 and 8) and temperature (30 °C), however, they exhibited opposite responses to increasing background tryptone concentration. While hydrolysis converted DC to its isomer or epimer, the two bacterial strains converted DC to various biotransformation products through a series of demethylation, dehydration, decarbonylation and deamination. Findings from the study can be used to better predict the fate of DC in the environment.

第二代四环素抗生素多西环素（DC）的命运由于其广泛用途而在近年来引起了越来越多的关注。关于环境中DC的生物降解性知之甚少。这项研究的目的是针对纯细菌菌株在不同环境条件下的反应动力学和生物转化产物表征DC的生物转化。两种细菌菌株：内江短杆菌Brundundimonas naejangsanensis DD1和水产Sphingobacterium mizutaiiDD2是从鸡粪中分离得到的，并具有DC的生物转化能力。结果表明，两种菌株均以新陈代谢为基础，以胰蛋白as为主要生长底物生物转化DC。DD2比DD1具有更高的生物转化动力学。两种菌株的pH值（7和8）和温度（30°C）相似，但是它们对背景胰蛋白concentration浓度的增加却表现出相反的反应。当水解将DC转化为其异构体或差向异构体时，两个细菌菌株通过一系列脱甲基，脱水，脱羰基和脱氨基作用将DC转化为各种生物转化产物。该研究的发现可用于更好地预测环境中DC的命运。