Application of single-cell stable isotope probing approach to investigate N2-fixing microorganisms

Abstract:

Biological nitrogen fixation, a process through which nitrogen-fixing microorganisms reduce atmospheric nitrogen to bioavailable ammonia, is the main source of “new” nitrogen in the environment, regulates primary productivity and thus affects the balance of nitrogen storage. Because most of nitrogen-fixing microorganisms in the environments are yet uncultured, culture-independent single-cell techniques with a high-level spatial resolution have become a powerful tool for studying nitrogen-fixing microorganisms. In addition, ¹⁵N₂-stable isotope probing (SIP) provides a very direct means to characterize nitrogen fixation activity based on the amount or rate of ¹⁵N assimilated by microorganisms. This article reviews the latest progresses in applying two single-cell techniques of nanosecondary ion mass spectroscopy (NanoSIMS) and Raman spectroscopy integrated with ¹⁵N₂-SIP for studies of nitrogen-fixing microorganisms, including the discovery of novel active nitrogen-fixing species and their spatial distribution in the environment, symbiotic relationship with other organisms, cellular physiological states, etc. Perspective on future study of nitrogen-fixing microorganisms by single-cell Raman spectroscopy is provided.