Wednesday, November 7, 2007 - 11:35 AM
290-5
Stable Isotope Probing: A Direct Approach to Linking Microbial Communities to Soil Organic Matter Processes.
David D. Myrold1, Peter J. Bottomley1, and Mary Beth Leigh2. (1) Crop & Soil Science, Oregon State University, 3017 ALS Building, Corvallis, OR 97331, (2) University of Alaska Fairbanks, P.O. Box 757000, Institute of Arctic Biology, Fairbanks, AK 99775-7000
Stable isotopes, particularly 13C and 15N, have been used extensively during the past 50 years to study soil organic matter, its composition and turnover. More recently, these stable isotopes have been coupled with molecular methods to study the active members of the soil microbial community using a method known as stable isotope probing (SIP). The first applications of SIP used 13C-labeled compounds and followed their incorporation into microbial lipids, measured as phospholipid fatty acids (PLFA) using compound-specific isotope ratio mass spectrometry. In addition to following the fate of labeled carbon from simple organic molecules into the microbial community, this method has been extended to include complex organic carbon, such as root exudates and decomposing plant residues. More recently, SIP applications have traced 13C, or less frequently 15N, into DNA and RNA. The labeled nucleic acids can be separated from unlabeled nucleic acids by equilibrium density centrifugation, isolated, and further analyzed by a wide range of molecular methods to determine the microorganisms that have assimilated the labeled substrate. The use of SIP with DNA or RNA provides much higher taxonomic resolution of the active microbial community than PLFA-SIP. We will provide an overview of the SIP techniques and provide examples of how they have been applied to study the relationship between microbial communities and soil organic matter processes. We will also suggest some addition ways that the principle of SIP might be coupled with other analytical techniques and used in future studies.