Presence of dissolved nucleotides in the North Pacific Subtropical Gyre and their role in cycling of dissolved organic phosphorus

Abstract

Dissolved and particulate nucleotide triphosphate (NTP) concentrations were measured in the upper 1000 m of the water column during 3 summer and 3 winter months at Stn ALOHA (22.75°N, 158°W) in the oligotrophic North Pacific Subtropical Gyre. In the euphotic zone (0 to 175 m) particulate adenosine-5'-triphosphate (P-ATP) and dissolved ATP (D-ATP) concentrations were positively correlated in summer (0 to 175 m; r 2 = 0.61, p < 0.001, n = 24), but not in winter (r 2 = 0.02, n = 24). D-ATP comprised > 65% of the total ATP (T-ATP) pool in the summer, and ~50% in winter. Dissolved guanosine-5'-triphosphate (D-GTP) inventories were 5-to 6-fold greater in July and August than those observed in mid-June (1.1 ± 0.1 vs. 8.0 ± 0.6 and 6.5 ± 0.3 µmol D-GTP m -2 , respectively) and winter concentrations were on average lower than the mean summer concentrations. The particulate GTP (P-GTP) inventories were almost twice those measured in winter (mean 1.1 ± 0.4 in summer vs. 0.6 ± 0.1 µmol P-GTP m -2 in winter, n = 3). These results are consistent with higher microbial growth rates in summer. Uptake of D-ATP showed multi-phasic kinetic patterns. The halfsaturation constants (K t ) ranged from 1 to 26 nM at D-ATP concentrations of 0.2 to 30 nM, and V max ranged from 0.3 to 1.4 nM d , and the turnover time of the ambient D-ATP pool was estimated to be 1 to 2 d. The P flux through the D-ATP pool could potentially be 5 times faster than that of the bulk DOP pool, implying that P derived from nucleotides may be an important pathway in the P cycle of oligotrophic oceans.

Response of &lt;i&gt;Nodularia spumigena&lt;/i&gt; to &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; – Part 3: Turnover of phosphorus compounds

“…4f). The turnover of dDNA and other DOP compounds (e.g., dATP, Azam and Hodson, 1977;Björkman and Karl, 2005) is very short, occurring within hours, so that shorter sampling intervals would have been necessary to estimate the variations. In addition, as mentioned above, Paul et al (1990) reported low dDNA production during the phytoplankton growth phase.…”

Organic phosphorus in the aquatic environment

“…5 0 -ATP and 5 0 -GTP have been identified in marine systems [55] whereas cAMP has been identified in lakes. [56] These nucleotides were identified using analytical biochemical reactions.…”

“…[60] For example in the North Pacific subtropical Gyre, because ATP is both rapidly produced and rapidly consumed, it was estimated that the P flux through the ATP pool was up to five times faster than the general organic P pool. [55] Similarly in a mesocosm experiment Løvdal et al [49] showed that the turnover time of ATP under P-limited conditions was only 5 min.…”

“…For example, ATP and GTP represented only ,0.1 % of the organic P pool in the surface water in the North Pacific Ocean. [55] Biogeochemistry Little is known about the biogeochemical cycling of the simple nucleotides in aquatic environments. They are obviously of biological origin and it has been suggested that peak production (and hydrolysis) occurs during algal blooms, at least in Antarctic marine waters.…”

Sargasso Sea phosphorus biogeochemistry: an important role for dissolved organic phosphorus (DOP)

“…Indeed, assays for the enzyme alkaline phosphatase (APase) suggest that DOP is readily utilized by the autotrophic community (Dyhrman et al, 2002;Lomas et al, 2004;Mather et al, 2008). Uptake measurements in oligotrophic gyres also indicate that the DOP pool is a potentially important source of P for autotrophs (Benitez-Nelson and Karl, 2002;Karl, 2003, 2005), particularly in the P-depleted North Atlantic (Casey et al, 2009;Orchard et al, 2010).…”