The influence of an anthozoan “host factor” on the physiology of a symbiotic dinoflagellate

Abstract

Anthozoan host factors are components of host animal homogenates which elicit the release of newly fixed carbon by symbiotic dinoflagellates in vitro. The host factor active component of an homogenate of the reef coral Pocillopora damicornis has recently been isolated and identified as a mixture of free amino acids. A synthetic host factor (SHF) based on the measured free amino acid pool of P. damicornis elicits an identical response in symbiotic dinoflagellates in vitro as does the crude host factor. SHF was used as a tool with which to investigate the impact of anthozoan host factor on other aspects of symbiotic dinoflagellate metabolism. Here we demonstrate that dinoflagellates isolated from the tropical sea anemone Aiptasia pulchella (Carlgren) incubated in SHF, in addition to releasing fixed carbon, also exhibit higher photosynthetic carbon fixation, heterotrophic carbon fixation, photosynthetic oxygen production, respiration rates, and cell specific concentrations of chlorophyll a as compared to dinoflagellates incubated in sea water in vitro. Thus, the performance of symbiotic dinoflagellates in vitro appears to be sustained in an amino acid rich environment, but compromised in sea water. This observation raises the possibility that in nature symbiotic dinoflagellates released from anthozoan hosts may survive in amino acid rich environments such as fish guts and “intermediate hosts”.