The outermost surface structures in chroococcacean cyanobacteria

Abstract

This is the first comparative study on the nature and occurrence of the outermost surface structures in chroococcacean cyanobacteria. It shows that all the structures are similar to those of other bacteria and not specific to only cyanobacteria. Twenty-two chroococcacean strains (1 Microcystis, 7 Synechocystis, 12 Synechococcus, and 2 Gloeothece) were included in the study. Two Synechocystis strains had a glycocalyx layer. The two Gloeothece strains had a characteristic sheath, and the space between the sheath and the cells contained loosely packed material. On the basis of their preferential staining with ruthenium red, both the sheath and the loosely packed material most probably consist of acidic polysaccharides. Microcystis firma, three Synechocystis strains, and one Synechococcus strain were surrounded by a regularly structured surface layer consisting of hexagonally arranged subunits. Microcystis firma, all seven Synechocystis, and three Synechococcus strains possessed pili. The pili of some strains occurred as bundles. None of the strains produced spinae. Additionally, some structures described in previous studies are reinterpreted according to the findings of the present study.