ABSTRACT
The natural abundance of isotopes has been the thrust of previous chapters. In this chapter we focus on the use of isotopically labeled compounds to investigate various biological processes in natural systems and contaminant biodegradation processes. Isotopically labeled compounds can be used to identify microorganisms, examine microbial growth, microbial metabolic pathways, and biodegradation of natural organic compounds and organic contaminants. The use of isotopes in environmental studies relies on the incorporation of a substrate that is highly enriched in a rare isotope, either radioactive or stable; the enriched radioactive or stable isotopic signal improves detection and quantication from the natural signal. Examples of specic radioactive and stable isotopes commonly used in tracer investigations include 14C,
10.1 Introduction ................................................................................................. 327 10.2 Analytical and Availability Considerations................................................. 328 10.3 Nitrogen ....................................................................................................... 331
10.3.1 13Nitrogen ....................................................................................... 331 10.3.2 15Nitrogen ........................................................................................ 333
10.4 Carbon ......................................................................................................... 335 10.4.1 13Carbon Contaminant Studies ....................................................... 336
10.5 The Use of Stable Isotopes to Examine Cellular Components ................... 337 10.5.1 Dual Isotopes and Dual Isotope Labeling ...................................... 338
10.6 Stable Isotope Probing (SIP) .......................................................................340 10.6.1 Phospholipid Fatty Acids (PLFAs)–Stable Isotope
Probing (SIP) .................................................................................. 341 10.6.2 Deoxyribonucleic acid DNA-Stable Isotope Probing (SIP) ........... 341 10.6.3 Ribonucleic acid (RNA)–Stable Isotope Probing (SIP) .................. 343
10.7 Conclusion ................................................................................................... 345 Acknowledgments ................................................................................................. 345 References .............................................................................................................. 345
3H, 35S, 13C, 15N, 2H, 37Cl, and 18O. This chapter will focus primarily on enrichments of 13/15N, 13C, and their combination and more briey on 3H.
