Cyanobacteria were essential for the developing of more complicated life forms. They produced the oxygen in our atmosphere. This oxygen is needed for the much more energy efficient metabolism of multicellular organisms. Moreover, the photosynthetic abilities of bacteria were presumably incorporated by the more advanced organisms. At present bacteria have an essential role in the recycling of matter.
Bacteria are everywhere.
Inside your mouth live more bacteria than the number of people who have ever lived. The little animation on the left shows spirochete bacteria. They are fast movers that have several flagella laying inside the cell. Click thumbnail to see large image of a Cyanobacteria Spirochetes photographed by Steve Durr, from his Micscape article about a Quekett Microscopical Club's trip to Epping Forest picturing many nice bacteria and protozoa.