Particulate polyphosphate and alkaline phosphatase activity across a latitudinal transect in the tropical Indian Ocean

Abstract

Polyphosphate (polyP) is an essential chemical constituent of microbial cells, and is hypothesized to play important roles in the marine biogeochemistry of phosphorus. However, polyP has only rarely been measured in the oceans. Here, we present data on the distribution of polyP across a latitudinal transect in the tropical Indian Ocean. PolyP concentrations (quantified as molar equivalents of a synthetic polyP standard) and ratios of polyP to total particulate phosphorus (TPP) along the transect ranged between 3-7 nmol eq. L 21 (polyP concentration) and 0.2-0.4 nmol eq. nmol 21 (polyP : TPP ratio), which is very similar to values reported from the North Pacific Subtropical Gyre. Yet unlike in the North Pacific, soluble reactive phosphorus was depleted to low concentrations ( 0.03 lmol L 21 ), and alkaline phosphatase activity was relatively high (1-4 nmol P L 21 h 21 ) along our cruise track. We attribute these results to the unique seasonal changes in iron and macronutrient supply in the Indian Ocean, which are caused by the monsoonal reversal in ocean currents. PolyP concentrations and polyP : TPP ratios decreased sharply with depth down to 150 m, suggesting that polyP was preferentially recycled relative to TPP, unlike in the North Pacific Subtropical Gyre. We hypothesize that alkaline phosphatase exerts a significant control over marine polyP biogeochemistry.

Dynamic polyphosphate metabolism in cyanobacteria responding to phosphorus availability

“…Our results suggest accumulation of polyP in all stages of cell growth, and high polyP accumulation was observed in some strains under high P levels (e.g., polyP:TPP in PCC6803 was high, > 0.5 mol eq mol −1 under P ranging from 0 to 150 μmol L −1 ), contrasting to the hypothesis that substantial polyP accumulation only takes place upon severe and persistent P stress (Martin et al, ). We also conclude that polyP:TPP is strongly dynamic responding to P availability and growth conditions (e.g., growth rates, etc.).…”

“…Polyphosphate metabolism as a response to P deficiency is important for both physiological functions of aquatic microbial communities and biogeochemical cycling on ecosystem scales (Mazard et al, ; Martin et al, ). Recent studies on polyP dynamics in marine environments have observed enrichment of polyP in marine planktonic cells in waters covering wide ranges of P levels, including, for example, the P‐rich temperate western North Atlantic, the ultra‐low‐P Sargasso Sea, the tropical Indian Ocean, the North Pacific subtropical gyre and a coastal Pacific fjord (Diaz et al, ; ; Orchard et al, ; Martin et al, ; ). PolyP:TPP ratio was commonly analysed as an important cellular polyP quota for understanding polyP dynamic response to P availability.…”

“…Variations in polyP:TPP ratios in marine waters were attributed to nutrient biogeochemistry rather than community composition, based on measurements of polyP: TPP in Synechococcus using cell‐sorting cytometry (Martin et al, ) and the analyses of microbial community composition (Martin et al, ). However, our results of three cyanobacteria strains suggest variability among different species of cyanobacteria in the ability to accumulate polyP, even within the same genus (two species of Synechococcus ; Table ).…”

“…Recent studies on polyP dynamics in marine environments have revealed the importance of polyP metabolism in both microbial physiology and biogeochemical cycling on the ecosystem scale (Orchard et al, ; Martin et al, ; ; Diaz et al, ; Dijkstra et al, ). For example, high polyP levels observed in low P Sargasso Sea were considered as P deficiency responses (Martin et al, ), whereas results from other systems with relatively higher P levels (e.g., the temperate western North Atlantic, North Pacific subtropical gyre and the tropical Indian Ocean) showed lower polyP accumulation (Diaz et al, ; Martin et al, ; ). However, the controls of polyP variability were not entirely clear.…”

“…However, the controls of polyP variability were not entirely clear. Much of the recent works on aquatic polyphosphate were large‐scale environmental studies (Diaz et al, ; ; Orchard et al, ; Martin et al, ; ), and detailed laboratory studies for polyP dynamics under amended P levels (P replete vs. P deplete) are needed but highly scarce, with only a few laboratory incubations studies available (Rhee, ; Jensen and Sicko‐Goad, ; Jacobson and Halmann, ; Orchard et al, ; Martin et al, ; Diaz et al, ). Lack of data for statistical analyses and differences in quantification methods complicate the comparsion the results of different studies.…”