the invention relates to a novel method for the in - vivo labeling of biopolymers such as proteins , nucleic acids , lipids , carbohydrates and biodegradable plastic using isotopes , especially stabile isotopes . the invention also relates to the use of chemolithotrophic bacteria for the in - vivo isotopic labeling of biopolymers . in particular , the invention relates to the use of co 2 - fixing bacteria , such as ralstonia eurtropha and related methanogenic bacteria for the in - vivo isotopic labeling , especially for labeling using the stable isotope 13 c alone and in combination with other isotopes . in addition , the invention relates to the use of isotropically labeled biomolecules in therapeutic and diagnostic applications , especially in spectroscopic methods and generally as tracers .