Original paper
Cytomorphology of the smallest picoplanktic Cyanobacteria
Šmarda, Jan; Šmajs, David
Algological Studies/Archiv für Hydrobiologie, Supplement Volumes No. 94 (1999), p. 333 - 351
17 references
published: Sep 16, 1999
DOI: 10.1127/algol_stud/94/1999/333
ArtNo. ESP142012900027, Price: 29.00 €
Abstract
Cell sizes of 14 strains or isolates of unicellular picocyanobacteria were measured with a high accuracy and their ultrastructure studied following their freeze-fracturing preparation; only strains (isolates) of cell diameter up to 2 µm were followed. The global ultrastructure of all appeared very simple, mostly the same. In centroplasm, DNA and peroxisomes were found, in exoplasm, ribosomes, 2-5 concentric (or confocal) parietal thylakoids (for the genus Cyanobacterium, numerous thylakoids, parallel to each other and to the long cell axis, are specific), polyphosphate and cyanophycin granules and solitary vesicles were present. In sections, in addition, dense phycobilisomes were found attached at the thylakoid surface. 3-layered cell wall was always the same, velvet-smooth, covered with very poor mucilaginous sheath. No aerotopes were seen. All strains were formed by short rod cells (in the genus Synechococcus) or by extremely short, relatively wide ellipsoid cells (in the genus Cyanobium) or by larger ellipsoid cells of analogous parameters (in the genus Cyanobacterium). All cells showed a clear tendency to bending. All cells divided by binary fission to two equal daughter cells, always in one direction, perpedicular to the longer axis of the cells: those of Synechococcus by cleavage, those of Cyanobium and Cyanobacterium by pinching. The average length of the cells of all strains varied between 0.8-3.9 µm, width between 0.6-2.0 µm; the length: width ratio between 1.12: 1-2.86:1. Contrary to the very similar, simple inner structure of cells of all strains, cell shape and size was unique for each one examined. Cytomorphological differences between the three genera examined are minimal; in spite of that, they are sufficient for a clear-cut delimitation of Synechococcus, Cyanobium and Cyanobacterium.
Keywords
Picoplankton • cyanobacterial cells • cell form • cell dimensions • cell ultrastructure • phase-contrast microscopy • electron microscopy • generic diacritical markers • taxonomy