硝化作用研究的新发现:单步硝化作用与全程氨氧化微生物

Recent discovery in nitrification:One-step nitrification and complete ammonia oxidizing microorganisms

硝化作用是氨被微生物氧化为硝酸盐的过程,分别由氨氧化微生物(AOB和AOA)和亚硝酸盐氧化细菌(NOB)主导完成.一个世纪以来,我们把这个分步硝化过程当成唯一的硝化途径来学习和研究.虽然根据动力学理论推测,环境中应该存在单步硝化作用,即由一种微生物单独完成整个硝化过程,将NH_3氧化为NO_3^-,但一直没有研究能直接证明该种微生物的存在.直到2015年底,3个科研团队分别在不同环境中发现了3种不同的经过纯培养的细菌(Candidatus Nitrospira nitrosa、Candidatus Nitrospira nitrificans和Candidatus Nitrospira inopinata)和一种未经过纯培养的细菌(类Nitrospira),它们都具备单独将氨氧化为硝酸盐的能力,这些微生物被定义为全程氨氧化微生物(Comammox).单步硝化作用和全程氨氧化微生物的发现终结了传承百年的理论,并引发了众多关于全球氮素循环的重要科学问题,如这些微生物在环境中的生态位点及其在硝化作用中的相对贡献等.本文就单步硝化作用及全程氨氧化微生物的发现作了简要概述.

Nitrification is the process of microbial oxidation of ammonia to nitrate, completed by the ammonia oxidizers （AOB and AOA） and nitrite oxidizing bacteria （NOB）, sequentially. For a cen-tury, we have been learning and studying the established two-step process as the unique way for nitrification. According to the kinetic theory, there should be a one-step nitrification in the environ-ment, that is, the whole process of nitrification （from NH3 to NO3- ） was completed by one microor-ganism, but no study could give a direct proof for the existence of this microorganism. Until the end of 2015, three different cultivated bacteria （Candidatus Nitrospira nitrosa, Candidatus Nitrospira hi-trificans and Candidatus Nitrospira inopinata） and an uncultivated bacterium （Nitrospira-like orga-nism） respectively found in different environments by three research teams, were defined as com-plete ammonia oxidizing microorganisms （Comammox）, because all of them could carry out the complete oxidation of ammonia to nitrate. The discovery of one-step nitrification and Comammox en-ded the 100-year-old dogma, and triggered many important scientific issues of the global nitrogen cycle, such as the ecological niche of these microorganisms in the environment and their relative contribution in nitrification. This paper made a brief overview of the discovery of one-step nitrification and Comammox.