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 Synech ococcus Nageli, of some species of tropical marine dinoflagellates wer e investigated for the presence of nitrogenase, phycoerythrin (PE) and ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO). The dinofl agellates Ornithocercus magnificus Stein, and O. steinii Schutt were c ollected in the Caribbean Sea, and transmission electron microscopy re vealed that, in addition to phaeosomes, bacterial consorts were also p resent between the upper and the lower girdle list of the cingular gro ove. The bacteria were uniform in size, ranging between 0.2 and 0.3 mu m approximately. Immunogold labelling techniques indicated that the c yanobacterial phaeosomes contained high amounts of the photosystem II associated pigment PE. The CO2-fixing enzyme RUBISCO was mainly locate d in carboxysomes. Those examined for nitrogenase were collected at bo th day and night, but nitrogenase was not detected. Ornithocercus spp. are non-photosynthetic organisms, and it appears that phaeosomes serv e as a carbon source for species of this genus, i.e. they have the fun ctional role of chloroplasts.