1999 Volume 53 Issue 1 Pages 29-37
Brownish yellow microbial mats growing along the Kakuma River and at the controlling pond in the Kakuma Campus of Kanazawa University are of predominantly iron oxidizing bacteria, such as Leptothrix sp., Gallionella sp. and Toxothrix sp. Those microbial mats use ferrous ions as their energy source through the oxidation into ferric ions. Transmission electron microscopy of the primitive microbial mat, have revealed mucoid substances of Toxothrix sp. like polysaccharides are effective for adhesion of iron hydroxides produced through biomineralization of Toxothrix sp. Iron hydroxides coated with mucoid substances are coagulated into colloidal particles 200nm in size. Such condensed colloidal iron hydroxides grow into the aggregates and subsequently may be expelled outward from the thin membrane of polysaccharides. It is suggested that polysaccharides of Toxothrix sp. prevent dispersion of iron hydroxides and promote coagulation of iron materials. Such a condensation process of iron hydroxides is considered to be a factor for increasing the thickness of microbial mats.
