How Do Bacteria Respire?

Like all living organisms, bacteria need to respire.

What is respiration?

Respiration is a chemical reaction that takes place in cells converting food (glucose) to energy. The energy is required so that living things can carry out the life processes (MRS GREN).

Aerobic respiration

Bacteria can respire using oxygen, this is called aerobic respiration. Bacteria, such as Mycobacterium tuberculosis, which causes the disease TB (tuberculosis), lives in the oxygen rich environment of the lungs and respires aerobically.

The word equation for aerobic respiration is:

Glucose + oxygen → carbon dioxide + water + ATP (energy)

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

There are also many bacteria that can respire without using oxygen. This is called anaerobic respiration.

Making vinegar using aerobic respiration

Vinegar is a dilute solution of ethanoic acid. It is used to flavour foods and is a useful preservative. It will keep pickled foods fresh for much longer.

The usual way to make vinegar is to ferment beer, wine or cider a second time, using cultures of a bacterium called Acetobacter. The organism respires aerobically, using oxygen to oxidise the ethanol (alcohol) to ethanoic acid.

Anaerobic respiration

The anaerobic breakdown of glucose from foods into either lactic acid or ethanol (alcohol) and carbon dioxide is called fermentation

glucose → ethanol + carbon dioxide + ATP

Making cheese and yoghurt using anaerobic respiration

Both cheese and yoghurt are produced by a group of organisms called lactic acid bacteria. Two species commonly used in both yoghurt and cheese production are different species of Lactobacillus and Streptococcus. Both of these ferment lactose (milk sugar) in milk to lactic acid. This is anaerobic respiration as no oxygen is required.

glucose → lactose → lactic acid + ATP

Making biofuels (biogas) using fermentation

Biogas is made in large tanks which contain several different types of micro-organisms, including anaerobic bacteria called methanobacteria. They use carbohydrates in the waste organic matter as a food source, breaking it down into methane gas and some carbon dioxide. The biogas burns well and can be used by farmers as an extra source of energy.