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New pathways for ammonia conversion in soil and aquatic systems

机译：土壤和水生系统中氨转化的新途径

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Ammonia conversion processes are essential for most soil and aquatic systems. Under natural conditions, the many possible reactions are difficult to analyze. For example, nitrification and denitrification have long been regarded as separate phenomena performed by different groups of bacteria in segregated areas of soils, sediments or aquatic systems sequentially in time. It has now been established that strict segregation in place and time of the two processes is not necessary and that both denitrifiers and nitrifiers have versatile metabolisms. However, the rates described for aerobic denitrifiers are very low compared to the rates observed under anoxic conditions. Also the rates of nitrifier denitrification are quite low, indicating that these conversions may not play an important role under natural conditions. In addition, these processes often result in the emission of quite large amounts of undesirable products, NO and N2O. Heterotrophic nitrification might be of relevance for systems, that contain a high carbon to nitrogen ratio. Recently, a novel process (Anammox) has been discovered in which ammonium serves as the electron donor for denitrification of nitrite into dinitrogen gas. N-15 labeling studies showed that hydrazine and hydroxylamine were important intermediates in this process. Enrichment cultures on ammonium, nitrite and bicarbonate resulted in the dominance of one morphotypical microorganism. The growth rate of the cultures is extremely low (doubling time 11 days), but the affinity for ammonium and nitrite and the conversion rates (9.2 10(-4) mol kg(-1) s(-1)) are quite high. Some of the reported high nitrogen losses in soil and aquatic systems might be attributed to anaerobic ammonium oxidation. In addition, this conversion offers new opportunities for nitrogen removal, when it is combined with recently developed processes for partial nitrification.
机译：氨转化过程对于大多数土壤和水生系统至关重要。在自然条件下，许多可能的反应很难分析。例如，硝化和反硝化长期以来一直被认为是由不同种类的细菌按时间顺序依次在土壤，沉积物或水生系统的隔离区域中进行的独立现象。现已确定，不需要两个过程在时间和地点上严格分开，反硝化器和硝化器均具有多种新陈代谢。但是，与在缺氧条件下观察到的速率相比，好氧反硝化器的速率非常低。硝化器的反硝化率也很低，这表明这些转化在自然条件下可能不会发挥重要作用。此外，这些过程通常会导致排放大量不想要的产物NO和N2O。异养硝化可能与碳氮比高的系统有关。最近，发现了一种新方法（Anammox），其中铵用作将亚硝酸盐反硝化成二氮气体的电子供体。 N-15标记研究表明，肼和羟胺是该过程中的重要中间体。在铵，亚硝酸盐和碳酸氢盐上的富集培养导致一种形态典型微生物的优势。培养物的生长速度极低（倍增时间11天），但对铵盐和亚硝酸盐的亲和力和转化率（9.2 10（-4）mol kg（-1）s（-1））很高。据报道，土壤和水生系统中氮的大量流失可能归因于厌氧铵氧化。此外，与最近开发的部分硝化工艺结合使用时，这种转化为脱氮提供了新的机会。

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