Bacteriopolis

To make this colorful culture, we mixed bucket loads of mud from a pond in Golden Gate Park together with eggs and toilet paper. Yum. The ultimate low-maintenance exhibit, it can live and thrive indefinitely, requiring only sunlight and the occasional addition of water.

The different colors you see here come from different types of bacteria: Blue-green cyanobacteria absorb carbon dioxide (CO₂) and produce oxygen in much the same way that plants do. The orange-colored bacteria are iron oxidizers; they get their energy from the chemical decomposition of iron into rust. The grayish bacteria get their energy not from light, but by consuming cellulose, or plant fibers.

This exhibit is a giant version of a Winogradsky column, named after Ukrainian biologist Sergei Winogradsky. You can make your own by putting pond mud, newspaper, eggs, and water in a blender.

CYANOBACTERIA
Like plants, cyanobacteria absorb carbon dioxide (C0₂) and produce oxygen. Unlike plants, they absorb light with a blue-green pigment, called phycocyanin.

IRON OXIDIZERS
These orange bacteria live somewhat lower down, where there's less oxygen.

ANAEROBIC PHOTOSYNTHESIZERS
Anaerobic means these bacteria live where there's no oxygen. Photosynthesizers means they get energy from light.

CELLULOSE DEGRADERS AND SULPHUR REDUCERS
These gray bacteria do not harvest light, but instead get energy by consuming cellulose, or plant fibers.

Zoomable High-Resolution Image of Bacteriopolis. © GigaMicro.

Charkoudian, L. K., Fitzgerald, J. T., Khosia, C, and Champlin, A. 2010. “In Living Color: Bacterial Pigments as an Untapped Resource in the Classroom and Beyond.” © PLOS.