Atomic force microscopy study of pili in the Cyanobacterium Synechocystis sp PCC 6803

Atomic force microscopy (AFM) is now widely used method in life sciences, specifically for investigation of the microbial surfaces. Continuing the AFM research of various bacteria we studied pilus-like appendages of the unicellular cyanobacterium Synechocystis sp. PCC 6803. As known the Synechocystis 6803 wild type cells produce pili of two morphotypes distinguished by diameter, length, morphology and relative abundance. Thick pili (one morphotype) are identified with well-known bacterial type IV pili responsible for cell gliding motility; the function of thin pili (another morphotype) is still unknown. AFM has revealed differences in piliation of the motile (wild type) and non-motile (spontaneous mutant) strains of the cyanobacterium and allowed estimating real dimensions and quantity of pili. According to the data obtained non-motile mutant cells possess thick pili increased in number (to 3-5 times) and length (more than to 10 times) relative to the wild type cells, however, both strains do not differ in thin pili. The advantages of AFM over conventional electron microscopic techniques in comparative morphology of the bacterial cells are discussed.