Unusual Types of Bacteria (Part 1)

. Sheathed Bacteria

These bacteria are filamentous microorganisms surrounded by a tubelike structure called a sheath. The bacterial cells inside the sheath are gram-negative rods that become flagellated (swarmer cells) when they leave the sheath. The swarmer cells produce a new sheath at a relatively rapid rate. They are often found in polluted streams and in wastewater treatment plants. This group includes three genera: Sphaerotilus, Leptothrix, and Crenothrix. These bacteria have the ability to oxidize reduced

iron to ferric hydroxide (e.g., Sphaerotilus natans, Crenothrix) or manganese to manganese oxide (e.g., Leptothrix). 

. Stalked Bacteria

Stalked bacteria are aerobic, flagellated (polar flagellum) gram-negative rods that possess a stalk, a structure that contains cytoplasm and is surrounded by a membrane and a wall. At the end of the stalk is a holdfast that allows the cells to adsorb to surfaces. Cells may adhere to one another and form rosettes. Caulobacter is a typical stalked bacterium that is found in aquatic environments with low organic content. Gallionella (e.g., G. ferruginea) is another stalked bacterium that makes a twisted stalk, sometimes called “ribbon,” consisting of an organic matrix surrounded by ferric hydroxide. These bacteria are present in iron-rich waters and oxidize Fe2+ to Fe3+. They are found in metal pipes in water distribution systems.

. Budding Bacteria

After attachment to a surface, budding bacteria multiply by budding. They make filaments or hyphae at the end of which a bud is formed. The bud acquires a flagellum (the cell is now called a swarmer), settles on a surface, and forms a new hypha with a bud at the tip. Hyphomicrobium is widely distributed in soils and aquatic environments and requires one-carbon (e.g., methanol) compounds for growth. A phototrophic bacterium, Rhodomicrobium, is another example of budding bacteria.