Phospholipid fatty acid stable isotope probing techniques in microbial ecology

Abstract

This chapter reviews the methodologies used to present stable isotopically labeled substrates to microbial communities present in a wide range of environmental materials, and also discusses the wet chemical and instrumental methods used to determine compound-specific δ13C values of individual phospholipid fatty acid (PLFA). The different ways in which the δ 13C values obtained can be used to assess a variety of properties and activities of microbial communities in the environment are discussed in this chapter. The most widely used labeling techniques for PLFA- stable isotope probing (SIP) utilize 13C-enriched gases as substrates. The PLFA-SIP approach significantly extends conventional PLFA profiling methods by identifying PLFAs diagnostic of specific functional groups through their enhanced 13C signatures derived from the assimilation of applied 13C-substrate(s). In this respect, the approach has key resonances with current trends in the way that environmental microbial communities are being considered in terms of the functioning and stability of ecosystems, especially in relation to the importance of ecosystem services in the context of sustainable environments. The relative ease of preparing PLFA fatty acid methyl esters (FAMEs), combined with the high sensitivity of the gas chromatography combustion-isotope ratio mass spectrometry (GC-C-IRMS) method, makes PLFA-SIP an extremely robust methodology, which allows very large numbers of environmental samples to be studied.