Paper No. 180-2
Presentation Time: 8:35 AM
DNA THERMOMETRY AND O-ISOTOPIC COMPOSITION OF ORGANOPHOSPHORUS SOURCE MATERIALS: NEW TOOLS IN THE STUDY OF BIOGEOCHEMICAL CYCLING AND TRANSPORT OF P
A clear understanding of the cycling and transport of P and of the evolution of PO4 O-isotopic compositions includes knowledge of the O-isotopic composition of source organophosphorus material, which is derived primarily from cellular biomass. Several recent studies in our group using the technique of multi-labeled water isotope probing (MLWIP) to elucidate phosphoenzyme reaction mechanisms and attendant isotope effects, led to the finding that PO4 undergoes complete and rapid wholesale exchange of all 4 O atoms with intracellular water due to the action of a single ubiquitous, intracellular enzyme: inorganic pyrophosphatase (PPase). PPase catalyzes rapid, temperature-dependent O-isotopic equilibrium between dissolved inorganic PO4 and water at low temperatures (Blake et al 2005, Chang and Blake 2015). Thus, cellular compounds and biomass synthesized from the intracellular dissolved PO4 pool, (e.g. DNA) should also carry a temperature signature imprinted by PPase. We performed a series of controlled microbial culture experiments over a temperature range of 4 to 88°C to obtain a calibration of DNA-PO4—water—temperature relations, and we also determined the O-isotopic composition of organically-bound PO4 in total cellular biomass—the primary source of dissolved inorganic PO4 in marine, freshwater and soil environments—using a UV-based digestion method. These results and methods may be widely applied to studies of P cycling and sources and to the evolution of PO4 O-isotopic compositions in natural systems.