Growth and Extracellular Carbonic Anhydrase Activity of Zooxanthellae Symbiodinium sp. in Response of Zinc Enrichment

Widiastuti Karim,Richardus Kaswadji,Tri Prartono,Lily Maria Gorettipanggabean

doi:10.4308/hjb.18.4.157

Abstract

Coral reef communities contain a wide variety of mutualistic associations none more important than the relationship between corals and their symbiotic dinoflagellates of the genus Symbiodinium sp., commonly referred to as zooxanthellae. The function of Zinc (Zn) as cofactor of several enzyme systems such as extracellular carbonic anhydrase (extracellular CA) which catalyzes the interconversion of HCO 3 − and CO 2 . Concentrations of dissolved Zn in oligothropic waters are often very low therefore may limit the growth of zooxanthellae and their ability to fix CO 2 from seawater via the carbonic anhydrase. The aim of this research is to investigate the effect of various concentrations of Zn on the growth and extracellular CA activity in zooxanthellae. Cell density was monitored daily by enumeration with hemocytometer-type chamber (0.1 mm). Extracellular CA was measured in homogenized intact whole cell by a pH drift assay. Results revealed that Zn status strongly influences the growth rate and extracelullar CA activity in zooxanthellae. The specific growth rate and cell density increased two-fold whilst extracelullar CA activity increased 10.5 times higher than that in control with increasing concentrations of Zn from 0 to 80 nM, but decreased when Zn was over 80 nM. Under a concentration of 80 nM was not Zn limited culture, consequently the growth rate of zooxanthellae not dependent on CO 2 concentration yet offset by extracelullar CA activity.

Highlights

Coral reef communities contain a wide variety of mutualistic associations none more important than the relationship between corals and their symbiotic dinoflagellates of the genus Symbiodinium sp., commonly referred to as zooxanthellae (Veron 1995)
The highest cell density and spesific growth rate were on Zn concentration under 80 nM in culture medium whereas it was two-fold higher than that of control (Table 1)
Plots of spesific growth rate versus the concentration of Zn in culture medium (Figure 1) showed that the largest increases of spesific growth rate occured at relatively high Zn concentration (80 nM)

Summary

Introduction

Coral reef communities contain a wide variety of mutualistic associations none more important than the relationship between corals and their symbiotic dinoflagellates of the genus Symbiodinium sp., commonly referred to as zooxanthellae (Veron 1995). The harboring of these intracellular and phototrophic dinoflagellates (zooxanthellae) is credited for the long-term success and dominance of coral in shallow, tropical, nutrient-poor environments since the Triassic (Muscatine & Porter 1997; Stanley 2003). Unlike freeliving microalgae, those that exist in symbiosis do not have direct access to the relatively constant seawater dissolved inorganic carbon (DIC) pool (2.2 mM). Carbonic anhydrase is a large and diverse collection of Zn metalloenzymes that catalyze the equilibration of dissolved inorganic carbon species according to the following equation (Moroney et al 2001): HCO3- + H+

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