Assessing Microbial Activity and Degradation Pathways in the Environment by Measuring Naturally Occurring Stable Isotopes in Organic Compounds
Martin Elsner, Christian Griebler, Tillmann Lueders and Rainer U. Meckenstock
from: Applications of Molecular Microbiological Methods (Edited by: Torben L. Skovhus, Sean M. Caffrey and Casey R.J. Hubert). Caister Academic Press, U.K. (2014)
Assessing microbial degradation of organic compounds in the environment currently faces two challenges; (a) detecting and quantifying not only microbial populations, but also in situ activity in the environment; (b) transferring mechanistic insight into (bio)chemical transformation mechanisms from the laboratory to the environment. Compound-specific isotope analysis (CSIA) measures stable isotope ratios (e.g. 13C/12C, 2H/1H, 15N/14N, 18O/16O, 34S/32S) in single target compounds (e.g. anthropogenic pollutants, sulfate). Since light isotopes (e.g. 12C) are typically degraded faster, heavy isotopes (e.g. 13C) become enriched in the remaining target compound. CSIA can analyze this enrichment as a way to demonstrate and quantify in situ degradation. Since analysis is conduced at natural isotopic abundance, no label is necessary and information can be obtained directly in natural systems. This book chapter gives three illustrative examples of the power of CSIA. (i) High resolution sampling at a hydrocarbon-contaminated aquifer can relate maximal abundances in degrader genes (microbial potential) to steep gradients in 13C/12C isotope values (evidence of activity). (ii) Isotope analysis of multiple elements in the pesticide atrazine is able to elucidate the underlying bacterial transformation mechanism. (iii) Isotope fractionation can serve as a novel concept to demonstrate ongoing natural attenuation across scales at contaminated sites read more ...