Urine is a major waste product of human metabolism and contains essential macro- and micronutrients to produce edible microorganisms and crops. Its biological conversion into a stable form can be obtained through urea hydrolysis, subsequent nitrification, and organics removal, to recover a nitrate-enriched stream, free of oxygen demand. In this study, the utilization of a microbial community for urine nitrification was optimized with the focus for space application. To assess the role of selected parameters that can impact ureolysis in urine, the activity of six ureolytic heterotrophs (Acidovorax delafieldii, Comamonas testosteroni, Cupriavidus necator, Delftia acidovorans, Pseudomonas fluorescens, and Vibrio campbellii) was tested at different salinities, urea, and amino acid concentrations. The interaction of the ureolytic heterotrophs with a nitrifying consortium (Nitrosomonas europaea ATCC 19718 and Nitrobacter winogradskyi ATCC 25931) was also tested. Lastly, microgravity was simulated in a clinostat utilizing hardware for in-flight experiments with active microbial cultures. The results indicate salt inhibition of the ureolysis at 30 mS cm-1, while amino acid nitrogen inhibits ureolysis in a strain-dependent manner. The combination of the nitrifiers with C. necator and V. campbellii resulted in a complete halt of the urea hydrolysis process, while in the case of A. delafieldii incomplete nitrification was observed, and nitrite was not oxidized further to nitrate. Nitrate production was confirmed in all the other communities; however, the other heterotrophic strains most likely induced oxygen competition in the test setup, and nitrite accumulation was observed. Samples exposed to low-shear modeled microgravity through clinorotation behaved similarly to the static controls. Overall, nitrate production from urea was successfully demonstrated with synthetic microbial communities under terrestrial and simulated space gravity conditions, corroborating the application of this process in space.

中文翻译：

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再生性生命支持系统中用于尿液硝化的合成微生物群落的培养基优化，菌株相容性和低剪切模型微重力暴露。

尿液是人类新陈代谢的主要废物，并含有必需的大量和微量营养素，以生产可食用的微生物和农作物。可通过尿素水解，随后的硝化作用和有机物的去除，将其生物转化为稳定形式，以回收富含硝酸盐的物流，而无需氧气。在这项研究中，针对尿液硝化作用的微生物群落利用进行了优化，重点是空间应用。为了评估可能影响尿中尿素分解的选定参数的作用，在不同盐度，尿素和氨基下测试了六个尿素分解异养菌（Acidovorax delafieldii，Comamonas testosteroni，Cupriavidus necator，Delftia acidovorans，Pseudomonas fluorescens和Vibrio campbellii）的活性。酸浓度。还测试了尿素分解异养菌与硝化财团（欧洲硝化亚硝基杆菌ATCC 19718和硝化细菌winogradskyi ATCC 25931）的相互作用。最后，在重力调节器中利用硬件对活性微生物培养物进行飞行实验，对微重力进行了模拟。结果表明在30 mS cm-1时盐对尿素分解的抑制作用，而氨基酸氮以应变依赖性方式抑制尿素分解。硝化剂与C. necator和V. campbellii的结合导致尿素水解过程完全停止，而在德拉菲氏土壤杆菌中，观察到硝化不完全，亚硝酸盐未进一步氧化为硝酸盐。其他所有社区都确认了硝酸盐的产生；但是，其他异养菌株最有可能在测试设置中引起氧气竞争，并观察到亚硝酸盐积累。通过倾斜旋转暴露于低剪切模型微重力的样品的行为与静态对照相似。总体而言，在地面和模拟空间重力条件下，合成微生物群落已成功证明了尿素中硝酸盐的生产，从而证实了该方法在太空中的应用。