Does Bacteria Affect the Rusting of Iron?

The cruise ship Titanic is expected to disappear into a pile of rust during the next 20 years. The cause is a newly discovered species of bacteria, Halomonas titanicae, living on the rusty remains. The bacteria do not cause iron to rust but live off the rust already formed. Rust is the formation of iron oxide, a chemical reaction that occurs naturally. Some bacteria species accelerate the process of rust formation.

Rust Formation

• The formation of rust is a chemical process that takes place in the presence of iron, oxygen, water and some form of electrolyte (salt). It is a four-step reaction where iron (Fe) donates two electrons in the presence of oxygen and water. Oxygen (O) accepts the electrons, forming a bond with iron and creating iron oxide. The overall chemical reaction is 2Fe + 2H#2O + 3O#2 -> 2Fe#2O#3 (rust) + 2H#2O where # designates a subscript.

Rust Ecosystem

• Moist areas containing iron are often home to iron-oxidizing bacteria.

  Rust creates a microscopic ecosystem home to numerous species of bacteria. Scientists identified 27 different species of bacteria living on rusting remains of the Titanic two miles below the ocean surface. A foul-smelling sludge often identifies presence of bacteria inhabiting iron rust. Many iron-eating bacteria produce sulfur byproducts for sulfur-metabolizing bacteria that release hydrogen sulfide with a characteristic rotten egg smell. Hydrogen sulfide accounts for the foul odor.

Role of Bacteria in Rust Formation

• Bacteria are not directly responsible for formation of rust. However, bacteria can advance the process of rusting in iron. Bacteria metabolize iron as a food source and release iron oxide as a waste product, causing corrosion. Bacteria are converting iron metal into iron oxide. Bacteria also change the environment where they live. Iron metabolism is exothermic and gives off heat energy to accelerate chemical reactions including rust formation. Bacterial waste lowers pH, creating a more acidic environment where rust can form.

Problems Associated with Iron Bacteria

• Iron-metabolizing bacteria are generally found in soil, marine and fresh water habitats. Growth of these bacterial species often explodes in the presence of a source of iron. One common area of concern is well water containing iron. The water can have a foul odor and taste when iron-metabolizing bacteria are present. The bacteria are not dangerous when they are consumed. However, the water is generally unpleasant to drink. Presence of an orange-colored sludge is a key indicator that iron bacteria are present.