Physiological properties and genetic analysis related to exopolysaccharide (EPS) production in the fresh-water unicellular cyanobacterium Aphanothece sacrum (Suizenji Nori)

The clonal strains, phycoerythrin(PE)-rich- and PE-poor strains, of the unicellular, fresh water cyanobacterium Aphanothece sacrum (Suringar) Okada (Suizenji Nori, in Japanese) were isolated from traditional open-air aquafarms in Japan. A. sacrum appeared to be oligotrophic on the basis of its growth characteristics. The optimum temperature for growth was around 20 degrees C. Maximum growth and biomass increase at 20 degrees C was obtained under light intensities between 40 to 80 mu mol m(-2) S-1 (fluorescent lamps, 12 h light/12 h dark cycles) and between 40 to 120 mu mol m(-2) S-1 for PE-rich and PE-poor strains, respectively, of A. sacrum. I'urifled exopolysaccharide (EPS) of A. sacrurn has a molecular weight of ca. 10(4) kDa with five major monosaccharides (glucose, xytose, rhamnose, galactose and mannose; >= 85 mol%). We also deciphered the whole genome sequence of the two strains of A. sacrum. The putative genes involved in the polymerization, chain length control, and export of EPS would contribute to understand the biosynthetic process of their extremely high molecular weight El'S. The putative genes encoding Wzx-Wzy-Wzz- and Wza-Wzb-Wzc were conserved in the A. sacrurn strains FPU1 and FPU3. This result suggests that the Wzy-dependent pathway participates in the El's production of A. sacrum.