Free amino acids exhibit anthozoan "host factor" activity: they induce the release of photosynthate from symbiotic dinoflagellates in vitro.

Abstract

Reef-building corals and other tropical anthozoans harbor endosymbiotic dinoflagellates. It is now recognized that the dinoflagellates are fundamental to the biology of their hosts, and their carbon and nitrogen metabolisms are linked in important ways. Unlike free living species, growth of symbiotic dinoflagellates is unbalanced and a substantial fraction of the carbon fixed daily by symbiont photosynthesis is released and used by the host for respiration and growth. Release of frxed carbon as low molecular weight compounds by freshly isolated symbiotic dinoflagellates is evoked by a factor (i.e., a chemical agent) present in a homogenate of host tissue. We have identified this "host factore in the Hawaiian coral Pocillopora damicornis as a set of free amino acids. Synthetic amino acid mixtures, based on the measured free amino acid pools of P. damicornis tissues, not only elicit the selective release of 14C-labeled photosynthetic products from isolated symbiotic dinoflagellates but also enhance total "4CO2 fixation.Dinoflagellates freshly isolated from the Hawaiian coral Pocillopora damicornis and the Pacific giant clam Tridacna crocea and incubated in sea water with a crude homogenate of their own host tissue fix 14C02 in the light and release a substantial fraction of the fixed carbon to the incubation medium, principally as [14C]glycerol, [14C]alanine, and [14C]glucose. In contrast, release of labeled organic carbon compounds by freshly isolated dinoflagellates incubated in sea water alone is always significantly less. Moreover, as a crude homogenate of animal tissue from the one host species also induces dinoflagellates from another host species to selectively release fixed carbon, the inducing factor would appear to be nonspecific (1).Release of fixed carbon by symbiotic dinoflagellates has been demonstrated in several cnidarian symbioses. Although a host factor (HF) has never been identified, its properties, depending on the host, have been described as heat labile (1-3) or heat stable (1, 4), enhancing carbon fixation (2) or not enhancing carbon fixation (3), absent from aposymbiotic hosts but inducible by reinfection with dinoflagellates, constitutive in aposymbiotic hosts (5), evoking release of fixed carbon from cultured symbiotic dinoflagellates and free-living nonsymbiotic dinoflagellates, not evoking the release of fixed carbon from cultured symbiotic dinoflagellates and free-living nonsymbiotic dinoflagellates (5, 6), and behaving like a substance with a molecular mass of <10 kDa (3) or -1 kDa (5). Here we identify HF in the Hawaiian reef coral P. damicornis as a set of free amino acids (FAAs) that not only evoke the selective release of photosynthate from symbiotic dinoflagellates in vitro but also enhance dinoflagellate carbon fixation. P. damicornis and the tropical sea anemone Aiptasia pulchella were collected from Checker Reef adjacent to the Hawaiian Institute of Marine Biology, Oahu, Hawaii, and the animals were transported by air to the University of California, Los Angeles. The c...

Differential nitric oxide synthesis and host apoptotic events correlate with bleaching susceptibility in reef corals

“…The only previous study of NO in clade C Symbiodinium (Hawkins and Davy 2012) reported a temperature-induced downregulation of NO synthesis. This could be due to the use of cultured Symbiodinium cells rather than those sampled in hospite, as their physiology is likely to be different outside the host (Gates et al 1995). The nature of the treatments-rapid heating in the previous study versus a 1°C d -1 rate here-may also have contributed, as could sub-cladal differences in symbiont physiology.…”

Cultivating endosymbionts — Host environmental mimics support the survival of Symbiodinium C15 ex hospite

“…There is ample evidence that host homogenate can stimulate release of photosynthetic products from symbiotic algae of giant clams, anemones, zoanthids and corals (Cook and Davy, 2001;Gates et al, 1995;Grant et al, 1997;Ishikura et al, 2004;Sutton and Hoegh-Guldberg, 1990;Trench, 1971). While a beneficial effect appears to be only valid for symbiotic and not for aposymbiotic hosts (Trench, 1971), there is also evidence for adverse effects of certain host homogenates (e.g., Sutton and Hoegh-Guldberg, 1990).…”

“…A synthetic cocktail representing the free amino acid pool measured in the coral P. damicornis (Gates et al, 1995), temporarily stabilized in vitro cultures of P. compressa symbionts. Incubation with host specific free amino acid cocktails (including the sulfonic acid taurine) in micro-to millimolar range can have a stimulating effect on fixation or release of carbon (Biel et al, 2007;Cook and Davy, 2001;Gates et al, 1995;Stat et al, 2008b;Wang and Douglas, 1997). While the general alleviating effect on physiological parameters of freshly isolated symbionts has been clearly demonstrated, its effect size is clade dependent (Gates et al, 1999;Stat et al, 2008b).…”

“…Glycerol supplement stock solutions were prepared in SSW, filter-sterilized and pH adjusted to 8.0. The amino acid supplement was based on the 'synthetic host factor' derived from P. damicornis (Gates et al, 1995). Individual concentrations were chosen as mean of the percentage of each compound in the two coral colonies originally investigated.…”

Baseline shifts in coral skeletal oxygen isotopic composition: a signature of symbiont shuffling?

“…To that end, studies have investigated the photophysiology of Symbiodinium either alone in culture, in culture with host factor (coral animal amino acids; Gates et al 1995), or in hospite. However, because most corals selectively associate with certain Symbiodinium clades (Goulet 2006), comparative studies of symbiont physiology within or isolated from a single host are less common.…”