IMMUNOLABELING OF PHYCOERYTHRIN, RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE AND NITROGENASE IN THE UNICELLULAR CYANOBIONTS OF ORNITHOCERCUS SPP (DINOPHYCEAE)

Phaeosomes, extracellular cyanobacterial symbionts of the genus Synechococcus Nageli, of some species of tropical marine dinoflagellates were investigated for the presence of nitrogenase, phycoerythrin (PE) and ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO). The dinoflagellates Ornithocercus magnificus Stein, and O. steinii Schutt were collected in the Caribbean Sea, and transmission electron microscopy revealed that, in addition to phaeosomes, bacterial consorts were also present between the upper and the lower girdle list of the cingular groove. The bacteria were uniform in size, ranging between 0.2 and 0.3 mu m approximately. Immunogold labelling techniques indicated that the cyanobacterial phaeosomes contained high amounts of the photosystem II associated pigment PE. The CO2-fixing enzyme RUBISCO was mainly located in carboxysomes. Those examined for nitrogenase were collected at both day and night, but nitrogenase was not detected. Ornithocercus spp. are non-photosynthetic organisms, and it appears that phaeosomes serve as a carbon source for species of this genus, i.e. they have the functional role of chloroplasts.