Formation of banded iron-manganese structures by natural microbial communities

Microbial structures in the form of banded zebra patterns have been found a s periodic iron-manganese layers in living biomats on the coast of Satsuma- Iwo Jima, a small volcanic island near southern Kyushu, Japan. Electron mic roscopic observation shows that coccus, fibrous, and bacillus-type bacteria l communities construct zebra architecture Fe-Mn layers through biominerali zation on and within cells. A living microbial fumarolic ferro-manganese pr ecipitation growing in seawater around an active volcanic island explains o ne mechanism of banded formation. Biological processes form the elemental z ebra pattern, with periodic distribution of bacterial cells with Fe-Mn in e ach layer of the architecture. Fibrous bacteria are sometimes mineralized w ith goethite, ferrihydrite, and buserite microcrystals, coated with granula r mucoid substances. The biomineralization may then mature to form a recent stratified banded-iron formation. The Satsuma-Iwo Jima zebra architecture is unusual in that it forms under aerobic conditions in a warm shallow-wate r environment, in contrast to the intermittent oxidizing and reducing condi tions in which deep-sea analogues develop.