Phosphorus limitation determines the quality of dissolved organic matter released by marine heterotrophic prokaryotes

Abstract

Marine heterotrophic prokaryotes (HP) generate copious amounts of dissolved organic matter (DOM). Some of this DOM is recalcitrant to biological degradation and can persist in the ocean for millennia. This carbon sequestration mechanism is called the microbial carbon pump (MCP). The factors controlling the strength of the MCP are still poorly understood. Phosphorus (P) limitation is a common condition in the ocean that can influence HP growth and metabolism. We addressed here the question of whether P-limitation affects the quantity and quality of DOM released by HP. We found no effect of P-limitation on HP-derived DOM net quantity. However, using fluorescence spectroscopy, we demonstrated that P-limitation altered DOM composition with an increase in humic-like compounds.Our study provides experimental evidence that P availability plays an important role in shaping the chemical composition of HP-derived DOM. Our results have implications for the fate of HP-derived DOM in the ocean, suggesting that P-limitation is a key driver of the MCP.

Bottom-up and top-down controls on Alteromonas macleodii lead to different dissolved organic matter compositions

“…1B ). Despite the role of substrate, the concentrations of DOM and inorganic nutrient also have a role in regulating bacterial growth as well as their products [ 48 , 49 ]. Our results imply that the substrate source/composition was a major factor controlling the growth of A. macleodii , which is in accordance with recent studies showing that source properties determine microbial degradation [ 50 , 51 ].…”

Effects of Phosphorus Limitation on the Bioavailability of DOM Released by Marine Heterotrophic Prokaryotes

“…Since little glucose (1.8 to 23.4 µmol C L -1 ) was remaining at the end of the cultures of the 1 st step, measured dissolved organic carbon (DOC) was assumed to re ect that released by the HP. This released DOC quanti cation and DOM characterization is described elsewhere [25]. In the 2 nd step of the experiment, the DOM derived from the bacterial strain and the HP communities was used as substrate for biodegradation experiments (Fig.…”

“…EEMs were separated into 6 distinct components using parallel factor analysis (PARAFAC) under the drEEM toolbox in MATLAB (Murphy et al, 2013). These results are described elsewhere [25].We used the protein-like component C 340 (ex 275/em 340) as an indicator of labile DOM and the microbial humic-like C 398 (ex 314 /em 398) as an indicator of recalcitrant DOM.…”

“…Using exudates of diatoms grown under P enriched and P depleted conditions, [23] showed that bacterial growth was signi cantly lower in the exudates from P depleted diatoms. However, while previous studies showed that P-limitation can in uence the HP extracellular metabolome [24] and HP-derived DOM (HP-DOM) optical properties [25,26], no studies have investigated the effects of P-limitation on the bioavailability of DOM released by HP.…”

“…In this study, we aimed to determine the bioavailability of DOM released by HP (a single bacterial strain and 2 natural HP communities from different seasons) grown under P-limitation and P-repletion. We have shown previously that HP-DOM released under P-limitation was enriched in humic-like uorescence [25] largely considered refractory [27][28][29][30], while under P-repletion protein-like uorescence, considered labile [31][32][33], prevailed. We hypothesize that (i) DOM released under P-limitation would thus promote lower prokaryotic growth and that (ii) the labile protein-like uorescence would decrease during the incubation contrary to the likely refractory humic-like DOM.…”