Biotic and Abiotic Pathways of Phosphorus Cycling in Minerals and Sediments: Insights from Oxygen Isotope Ratios in Phosphate

Abstract

A key question to address in the development of oxygen isotope ratios in phosphate (δ(18)O(p)) as a tracer of biogeochemical cycling of phosphorus in ancient and modern environments is the nature of isotopic signatures associated with uptake and cycling of mineral-bound phosphate by microorganisms. Here, we present experimental results aimed at understanding the biotic and abiotic pathways of P cycling during biological uptake of phosphate sorbed to ferrihydrite and the selective uptake of sedimentary phosphate phases by Escherichia coli and Marinobacter aquaeolei. Results indicate that a significant fraction of ferrihydrite-bound phosphate is biologically available. The fraction of phosphate taken up by E. coli attained an equilibrium isotopic composition in a short time (<50 h) due to efficient O-isotope exchange (between O in PO(4) and O in water; that is, actual breaking and reforming of P-O bonds) (biotic pathway). The difference in isotopic composition between newly equilibrated aqueous and residual sorbed phosphate groups promoted the ion exchange (analogous to isotopic mixing) of intact phosphate ions (abiotic pathway) so that this difference gradually became negligible. In sediment containing different P phases, E. coli extracted loosely sorbed phosphate first, whereas M. aquaeolei preferred Fe-oxide-bound phosphate. The presence of bacteria always imprinted a biotic isotopic signature on the P phase that was taken up and cycled. For example, the δ(18)O(p) value of loosely sorbed phosphate shifted gradually toward equilibrium isotopic composition. The δ(18)O(p) value of Fe-oxide-bound phosphate, however, showed only slight changes initially but, when new Fe-oxides were formed, coprecipitated/occluded phosphate retained δ(18)O values of the aqueous phosphate at the time of formation of new Fe oxides. Concentrations and isotopic compositions of authigenic and detrital phosphates did not change, suggesting that these phosphate phases were not utilized by bacteria. These findings support burgeoning applications of δ(18)O(p) as a tracer of phosphorus cycling in sediments, soils, and aquatic environments and as an indicator of paleo- environmental conditions.

Organic phosphorus in the aquatic environment

“…Carbon ( 12 C/ 13 C), nitrogen ( 14 N/ 15 N), oxygen ( 16 O/ 18 O), sulfur ( 32 S/ 34 S) and hydrogen ( 1 H/ 2 H) all have stable isotopes that have, or could be used in studying P dynamics. For example, changes in 18 O to 16 O ratios in phosphate have been used to determine the source of P to sediments [139] and to differentiate between biotic and abiotic cycling of P. [140] Although those studies focussed on phosphate, similar approaches could be applied to organic P.…”

Dissolution and Microstructural Transformation of ZnO Nanoparticles under the Influence of Phosphate

“…Application of phosphate fertilizers has released large amounts of phosphate into surface and underground waters. 25 Municipal waste waters and industrial effluents usually contain large amounts of phosphate and have a high potential to release phosphate into the environment. Therefore, interaction between NPs and phosphate in the natural aqueous environment is inevitable.…”

Phosphorus Dynamics and Availability in the Nearshore of Eastern Lake Erie: Insights From Oxygen Isotope Ratios of Phosphate

“…Compared to marine systems (Colman et al, 2005;McLaughlin et al, 2006aMcLaughlin et al, ,b, 2013Goldhammer et al, 2011;Jaisi et al, 2011;Joshi et al, 2015;Li et al, 2017) and soils (Zohar et al, 2010;Angert et al, 2012;Tamburini et al, 2012;Granger et al, 2017a), freshwater environments are poorly characterized with respect to δ 18 O P [but see Granger et al, 2017b;Pistocchi et al, 2017)]. The δ 18 O P we measured in the Grand River during April and early May (+9.4 ± 1.7 to +11.9 ± 0.7‰) are similar to values reported for Lake Erie tributaries in the central and western basins over summer and fall ), but lower than those reported for the River Taw, UK (Granger et al, 2017b).…”

“…The strong bond between oxygen and phosphorus atoms in phosphate are resistant to oxygen exchange under most environmentally relevant conditions (Paytan and McLaughlin, 2012). While isotopic fractionation effects of abiotic processes such as sorption and desorption appear to be relatively minor (Jaisi et al, 2010(Jaisi et al, , 2011, fractionation during biologically mediated enzymatic reactions can be large and at times, substrate and enzyme dependent (Blake, 2005;Blake, 2006, 2009). The uptake and internal cycling of P i by intracellular pyrophosphatases (EC 3.6.1.1) results in complete exchange of all oxygen atoms from P i with oxygen atoms from water, leading to a rapid temperature-dependent equilibrium between oxygen in P i and intracellular water (Longinelli and Nuti, 1973;Blake, 2005), which is expected to be equal to that of ambient water (δ 18 O W ) (but see Li et al, 2016b).…”