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Planes of successive divisions in Escherichia coli have been proposed to be either parallel or perpendicular to each other, restricted to one or two dimensions. To test the hypothesis that divisions can occur in planes alternating in three dimensions, a method was developed to generate cells with secondary constrictions during growth in suspension. The method involves a combination of thymine limitation (to manipulate chromosome replication rate) and mecillinam treatment (to inhibit penicillin-binding protein 2). The former modifies timing of terminations, the latter results in spheroidal cells. Such cells displayed secondary constrictions after adding deoxyguanosine (accelerating replication rate), thus temporarily enhancing division signals. The successive constrictions were seen to develop in planes that were tilted relative to each other, and in positions related to those of the nucleoids, visualized by staining with DAPI (4',6-diamidino-2-phenylindole dihydrochloride hydrate). Visualizing cell envelopes with FM 4–64 by confocal scanning laser microscopy supported the conclusion that planes of successive divisions can alternate in three dimensions.
The marine sponge Xestospongia muta (Porifera: Demospongiae: Haplosclerida) harbours cyanobacteria in its peripheral tissue that have been described as having an Aphanocapsa feldmanni-type appearance. Through subsequent cell fractionation steps we obtained a virtually pure cell suspension of the cyanobacteria. Through amplification of a region of the 16S rRNA gene we found that these cyanobacteria seem closely related to Prochlorococcus (Cyanobacteria, Prochlorophytes, Prochlorococcaceae), and Synechococcus (Cyanobacteria, Chroococcales, Synechococcus). We furthermore developed a new method, to obtain a clear signal with FISH by bleaching the auto-fluorescence of cyanobacteria, with osmium tetroxide. The location and morphological characteristics of the cyanobacteria are described by both light and electron microscopy.
The mechanisms that determine chromosome structure and chromosome partitioning in bacteria are largely unknown. Here we discuss two hypotheses: (i) the structure of the Escherichia coli nucleoid is determined by DNA binding proteins and DNA supercoiling, representing a compaction force on the one hand, and by the coupled transcription/translation/ translocation of plasma membrane and cell wall proteins, representing an expansion force on the other hand; (ii) the two forces are important for the partitioning process of chromosomes.
