The 28 strains of Nostoc were previously isolated and identified for their species by Thailand
Institute of Science and Technology Research (TISTR). Since a strain with a large cell size has an
advantage for cell harvesting, The cellular sizes of these Nostoc were determined under a light
microscope. The result showed that all the 28 strains have filamentous forms in which cells arrange
as in a linear line fasion and the relatively large cell size was found in strain number 24 (Nostoc sp.
strain E) and strain number 25 (Nostoc sp. strain F) (Fig. 1).