Uptake of dissolved free amino acids by the scleractinian coral Stylophora pistillata

Abstract

SUMMARYThis study was designed to assess the importance of dissolved free amino acids (DFAA) as a nitrogen source for the scleractinian coral Stylophora pistillata. For this purpose, experiments were performed using 15 N-enriched DFAAs, and % 15 N enrichment was measured both in animal tissue and zooxanthellae at different DFAA concentrations, incubation time and light levels. As previously observed for urea, which is another source of organic nitrogen, DFAA uptake exhibited a biphasic mode consisting of an active carrier-mediated transport for concentrations below 3·mol·l -1 and a linear uptake for higher concentrations. The value of the carrier affinity (K m =1.23·mol·l -1 DFAA) indicated good adaptation of the corals to the low levels of DFAA concentrations measured in most oligotrophic waters. DFAA uptake was also correlated with light. The DFAA contribution to the nitrogen requirements for tissue growth was compared to the contribution of ammonia, nitrate and urea, for which uptake was also measured in S. pistillata. Inorganic sources (NH 4 + and NO 3 -) contributed 75% of the daily nitrogen needs against 24% for organic sources. Taken altogether, dissolved organic and inorganic nitrogen can supply almost 100% of the nitrogen needs for tissue growth.

Scleractinian coral cell proliferation is reduced in primary culture of suspended multicellular aggregates compared to polyps

“…Restrictions of the intracellular availability of nitrogenous nutrients needed to undertake dinoflagellate cell cytokinesis is one of the processes which maintain dinoflagellates in a growth-limited state (Wooldridge 2010). In single dissociated cell cultures, the dissolved amino-acids contained in the complex cell culture medium are likely to be rapidly assimilated by the dinoflagellates (Grover et al 2008), fueling their cell growth and division. The expulsion or degradation of dinoflagellates by the host cell after the peak of CSD could explain the return to initial CSD.…”

A single-cell view of ammonium assimilation in coral–dinoflagellate symbiosis

“…Coral fragments were then attached to fine nylon fishing line and acclimatized to the mean local ambient temperature for a week in natural seawater in six independent flow-through aquarium tanks (60 l; three tank replicates per treatment). The ambient light levels were controlled throughout the experiment using shade cloths to mimic natural reef flat conditions (noon irradiance ranging from 700 to 1000 mmol À and ammonium, NH 4 þ ) to the nitrogen requirements of corals (Grover et al, 2008). (b) Schematic diagram of coral oral tissues structure (inset of A) indicating the location of the endosymbiotic dinoflagellates in the coral gastrodermal cells.…”

“…Among the different dissolved nutrients, ammonium is the preferred source of nitrogen for symbiotic corals ( Figure 1a) (Grover et al, 2002(Grover et al, , 2008. However, the relative contribution of coral and dinoflagellate cells to fix ammonium in this symbiosis has remained unclear.…”

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

“…Uptake of particulate and dissolved nitrogen from the seawater can satisfy the nitrogen demand of corals by >100%. Heterotrophic feeding on particulate nitrogen sources was considered to satisfy most of the coral's nitrogen demand (Houlbrèque and FerrierPagès, 2009), but also the uptake of dissolved nitrogen in the form of NH + 4 (42%), nitrate (34%), dissolved free amino acids (21%) and urea (3%) together can contribute up to 100% to the coral's nitrogen demand (Grover and Maguer, 2002;Grover et al, 2003Grover et al, , 2006Grover et al, , 2008. However, the uptake of external nitrogen sources is concentration-dependent and coral reefs experience strong seasonal and diel variation in dissolved and particulate nutrient availabilities (Grover and Maguer, 2002;Cardini et al, 2015).…”