Epifluorescence microscopy ofAnabaena sp.: Nucleoid configurations and evidence for inclusion-associated DNA

Vital staining of the nucleoid inAnabaena sp. PCC7118 was performed using the double stranded DNA-specific fluorochrome DAPI. In the unicellular mutant, the central epifluorescent zone had a dense skein configuration, while in the filamentous parent strain protrusions, lobes, and distinct isolated elements of the nucleoid were visible. Both variants contrasted with the mainly peripheral, partitioned structure typical of plastids and prochlorophytes. Blue-white emittance from the DNA-DAPI complex was maximum in dividing cells, suggesting that DNA configuration is linked to the cell cycle events. In stationary cultures, epifluorescent cell inclusions were conspicuous: based on this observation, we argue that DNA is associated with carboxysomes in situ.