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.