Winogradsky columns are an example of a self contained 'sulfuretum', where heterotrophic sulfate reducing bacteria (SRBs) and chemoautotrophic sulfide oxidizing bacteria (SOBs) exhange oxidants and redutancts in a carbon cycle that uses sulfur instead of oxygen as as the electron acceptor/donor. They are named for one of the 'fathers' of biogeochemistry, Sergei Winogradsky.
Two examples of Winogradsly columns. See: Winogradsky Column for the source of the picture above and the schematic below. I have had a 2-foot Wimogradsky column for about 10 years now. I'll get a picture of my pets as soon as I remember to bring the camera in to work.
Schematic of the realtive postions of the various bacterial communities in a Winogradsky column. In most cases the bacteria live in patches throughout the column.
Some of the chemical transformations involved in the bacterial sulfur cycle.