Abstract
Cyanobacteria are Gram-negative bacteria possessing the plasma membrane and the outer membrane. Cyanobacteria produce extracellular polysaccharides (EPS). It is considered that the EPS protects the cell from environmental stresses. The EPS is generally categorized into three types: lipopolysaccharides (LPS); capsular polysaccharides (CPS); and the released polysaccharides (RPS). To examine the relation between cell-surface structure and stress-defense mechanism in cyanobacteria, the gene which is involved in the Lipid-A biosynthesis of the outer membrane was disrupted in the filamentous cyanobacterium Anabaena sp. strain PCC 7120. The disruptant cells were more sensitive to various stresses than wild-type cells. The amounts of CPS and RPS of the disruptant cells were decreased in comparison with those of wild-type cells. We will discuss the correlation among the outer membrane, the EPS, and the stress-defense mechanism in cyanobacteria.
