Stable Isotope Probing Techniques Using H218O

This chapter reviews the use of 18O-water in stable isotope probing (SIP) studies. Research groups made important contributions to understanding of adenosine triphosphate (ATP) production in mitochondria and bacteria. Richards and Boyer, employing 18O-water, showed that oxygen atoms from water can be transferred to DNA inside E. coli cells. Subsequently, it was shown that 18O-water may also be used to label DNA formed in soil. Water is a small molecule and therefore can rapidly diffuse throughout the soil environment, so that the label is relatively homogenously distributed throughout the sample and all soil organisms are exposed to similar concentrations of label. However, it is unlikely that the label will be completely homogenously distributed in soil. SIP with 18O-water may also be used to study the impact of environmental conditions such as temperature or pH on microbial population dynamics in soil. Finally, SIP with 18O-water is suitable for studies on the impact of complex nutrient sources on microbial population dynamics in soil. For instance, it is well known that plant litter quality, often gauged by measuring the lignin to nitrogen ratio, affects decomposition rates and therefore multiple nutrient cycles in soil.