Fine structure and immunolocalisation of proteins in Aphanizomenon sp. from the Baltic Sea

The subcellular arrangement of vegetative cells in the colony-forming cyanobacterium Aphanizomenon sp., collected from blooms in the Baltic Sea in the summer of 1991 and 1992, was characterised by a loose network of thylakoids with intrathylakoid spaces. The phycobiliprotein phycoerythrin (PE) was found in vegetative cells at locations corresponding to thylakoids and similar relative quantities of PE were found in heterocysts; however, the subcellular location was ambiguous in heterocysts. Cellular inclusion bodies common in cyanobacteria, such as polyhedral bodies, cyanophycin and polyphosphate granules, were present in most vegetative cells but not in heterocysts. A large polyhedral crystal was present in both cell types. Antibodies against Rubisco did not bind to this inclusion but to the smaller polyhedral bodies (i.e. carboxysomes) and free Rubisco in the cytoplasm. In addition, gas vesicles were found to be exclusive to vegetative cells and occasionally microtubule-like inclusions and spherical membrane inclusions were observed. The putative Aphanizomenon flos-aquae from the Baltic Sea appears to be significantly different in ultrastructure from freshwater A. flos-aquae, and we recommend that, until differences are clarified, the Baltic form be referred to as Aphanizomenon sp.