Authors: David Porta Rosmarie Rippka Mariona HernándezMariné
Publish Date: 1999/12/21
Volume: 173, Issue: 2, Pages: 154-163
Abstract
Three unicellular cyanobacterial strains PCC 7425 PCC 8303 PCC 9308 assigned to the genus Cyanothece Komárek 1976 which showed an unusually high content of light refractile inclusions when viewed by phasecontrast microscopy were characterized by confocal laser scanning microscopy and transmission electron microscopy All strains had concentric cortical thylakoids and a compact central nucleoid Frequently the two innermost thylakoid membranes protruded to form circular enclosures containing cytoplasm or electrontransparent granules or both The largest granules were partially immersed in the nucleoid region but they remained attached to the inner cortical thylakoids by a single narrow connection The pattern of binary cell division in strain PCC 7425 was different than that in strains PCC 8303 and PCC 9308 In the former all cell wall layers invaginated simultaneously whereas in the latter the invagination of the outer membrane was delayed compared to that of the cytoplasmic membrane and the peptidoglycan layer Thus prior to completion of cell division the new daughter cells of strains PCC 8303 and PCC 9308 were transiently connected by a thick septum which was not observed in strain PCC 7425 Nucleoid partitioning coincided with initiation of cell division in all three strains and was unlike that reported in other bacteria and in archaea in which separation of the nucleoids precedes cell division Based on the common morphological and ultrastructural features the three strains of Cyanothece examined constitute a distinct cluster which might deserve independent generic status
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